Heat Sterilization Notes PDF

**HEAT STERILIZATION** Heat Sterilisation Overview Definition: Heating food at high temperature for a sufficient time to destroy microbial and enzyme activity. Shelf Life: Sterilised foods have a shelf life exceeding six months at ambient temperatures. Challenges: Traditional in-container steril...

**HEAT STERILIZATION** Heat Sterilisation Overview Definition: Heating food at high temperature for a sufficient time to destroy microbial and enzyme activity. Shelf Life: Sterilised foods have a shelf life exceeding six months at ambient temperatures. Challenges: Traditional in-container sterilisation can reduce nutritional and sensory qualities. Modern Advances: Reduced processing time. Aseptic processing: Foods processed before packaging. Emerging technologies like ohmic heating. In-Container Sterilisation Key Factors Affecting Processing Time: 1. Heat resistance of micro-organisms/enzymes in the food. 2. Heating conditions. 3. pH of the food. 4. Size of the container. 5. Physical state of the food. Heat Resistance of Micro-Organisms Important Considerations: Influenced by D (decimal reduction time) and z (temperature sensitivity) values. Clostridium botulinum (pH \> 4.5): Most dangerous pathogen, produces lethal botulin toxin. Acidic foods (pH \< 3.7): Less severe heating (pasteurisation) primarily for enzyme inactivation. Key Points on Microbial Destruction: Thermal destruction is logarithmic. Commercial sterility: Probability of survival of one microbe is minimal. Processes: 12D process: Reduces microbial numbers by 12 decimal reductions (e.g., for C. botulinum in low-acid foods). 2D--8D process: Used for foods with more heat-resistant spoilage micro-organisms to balance safety and quality. Factors Influencing Heat Penetration: Food Properties: 1. Type of product: Liquid/particulate foods (e.g., peas in brine): Heat faster via convection. Solid foods (e.g., meat paste): Heat slower due to conduction. 2. Container size: Smaller containers allow faster heat penetration. 3. Agitation: End-over-end agitation: Improves convection currents in viscous/semi-solid foods. Processing Environment: 4. Retort temperature: Higher temperature difference enhances heat penetration. 5. Container type: Metal heats faster than glass or plastic (thermal conductivity differences). 6. Container shape: Tall containers promote convection in convective heating foods. Key Observations in Quality Assurance: Swelling containers: Can indicate microbial growth or toxin production. Accelerated storage trials: Ensure commercial sterility before release. Thermal Death Time (TDT) and F Value TDT (F Value): Time required to achieve a specific reduction in microbial numbers at a given temperature. Expression: Denoted with suffixes indicating retort temperature and z value (e.g., F10 for 115°C and z=10°C). F0: Reference F value for 121°C and z=10°C. Calculation: Formula: F = D (\\log n\_1 - \\log n\_2) - n\_2: Final microbial count. Typical F0 values: Vegetables in brine: 3--6 min. Cream soups: 4--5 min. Meat in gravy: 12--15 min. Calculation of Process Times Purpose: Determine how long food in a given container size should be held at a set temperature to achieve required thermal destruction at the slowest heating point. Methods: 1. Mathematical Method: Based on equivalent lethality of time-temperature combinations. 2. Graphical Method: Uses heating and cooling curves to determine processing time. Extrapolates key values like and. Influencing Factors for Process Time G Factor: Influenced by: TDT of the micro-organism. Slope of the heating curve. Z value of the micro-organism. Difference between retort temperature and cooling water temperature. Cooling Lag Factor (jc): Accounts for additional heating during cooling. : Pseudo-initial product temperature at cooling start. : Initial product temperature at cooling start. Adjusted Processing Time Only 40% of come-up time (time to reach operating temperature) is effective for microbial destruction. Corrected Time Formula: \\text{Process time} = B -- 0.4l F1 and U Values F1: F value at retort temperature (e.g., Table 12.2). U: Ratio of reference F value to F1. U = \\frac{F}{F1} Summary Table: F1 Values (Selected z Values at Retort Temperatures Below 121°C) Adapted from Stumbo (1973). Convection Heating Foods: Lethal Rate Curve Analysis Lethal Rate Curve: Used to determine when heating should stop. A line is drawn parallel to the cooling portion of the curve to ensure the total enclosed area represents the required lethality. Example: Area under Curve ACE: 100.5 cm² = 10.05 min at 121°C (as 1 cm² = 0.1 min at 121°C). To reduce lethality to F₀ = 7 min (70 cm²), the process time is adjusted to 45 min. Conduction Heating Foods: Post-Heating Lethality Key Characteristics: The center temperature continues to rise even after cooling begins due to low heat transfer rates. Determination of Lethality: Requires multiple trials with heating stopped at varying times to determine sufficient microbial destruction. Improved General (Graphical) Method Principle: Integrated Lethality: Microbial destruction is a combined effect of temperature and time. Higher temperatures result in a logarithmic reduction in time needed for microbial destruction. Lethal Rate: A dimensionless number representing the reciprocal of the Thermal Death Time (TDT). Formula: \\text{Lethal Rate} = 10\^{(\\Theta -- 121) / z} : Temperature increase required for a 10-fold reduction in microbial TDT. Example Calculation: Processing temperature:. z-value:. \\text{Lethal Rate} = 10\^{(115 -- 121) / 10} = 0.25 Key Insights: Lethality contribution increases as the food approaches retort temperature, with most destruction occurring in the final minutes before cooling. Initial heating contributes minimally to total lethality. Practical Use of Lethal Rate Method Determines the impact of temperature-time combinations on microbial lethality. Allows flexible process adjustments to achieve equivalent lethality. Example: Table of Lethal Rate Values (for ) Advantages: Better suited for practical applications compared to rigid mathematical models. Useful for understanding equivalent temperature/time relationships. Sterilizing Retorts Retorts are categorized into batch and continuous systems, each with specific advantages and limitations: 1. Batch Retorts Types: Vertical: Compact design, requires less floor space. Horizontal: Easier loading/unloading, facilitates agitation but requires more floor space. Example: Orbitort Consists of concentric cages holding cans horizontally. Cages rotate to agitate contents for uniform heat distribution. 2. Continuous Retorts Ensure consistent processing conditions and uniform product quality. Gradual pressure changes minimize strain on container seams. Disadvantages: High in-process stock at risk during breakdowns. Potential issues with metal corrosion or thermophilic bacteria if not properly managed. Types: 1. Cooker-Coolers: Cans pass through pre-heating, sterilizing, and cooling sections on a conveyor. 2. Rotary Sterilizers: Slowly rotating drum moves cans through helical tracks inside a pressure vessel, ensuring mixing of contents. 3. Hydrostatic Sterilizers: Suitable for high-volume production (e.g., 1000 cans/min). Limited flexibility for frequent changes in container size or processing conditions. Automation and Control Computer systems monitor and control variables: Raw material temperature, cooling water temperature, steam temperature, processing time, and heating/cooling rates. Benefits: Minimized energy use. Precise lethality calculations. Methods of Heating 1. Heating by Hot Water Used for glass containers or flexible pouches under over-pressure of air. Glass: Slower heat penetration due to lower thermal conductivity and greater thickness. Pouches: Heat rapidly due to thin material, saving energy and reducing wall overheating. Processing orientation: Horizontal: Uniform food thickness. Vertical: Promotes better water circulation but requires special frames to prevent bulging. 2. Heating by Flames Direct flame heating at 1770°C for spinning cans. Advantages: High heat transfer rates reduce processing times, saving 20% energy compared to conventional methods. Smaller cans and no brine reduce transportation costs by 20--30%. Limitations: High internal pressures limit use to small cans. Examples: Mushrooms, sweetcorn, green beans, pears, cubed beef. 3. Heating by Saturated Steam Latent heat transfer: Steam condenses on the container surface. Air trapped inside the retort can cause under-processing due to the insulating boundary film. Venting: Removes air from the retort, ensuring uniform processing. Challenges: Slow heat penetration in solid or viscous foods leads to over-processing near container walls, damaging nutritional and sensory qualities. Improvements: Thinner containers. Agitation to enhance heat transfer. Cooling Process 1. Containers are cooled with water sprays. 2. Compressed air equalizes internal pressure, preventing seam strain. 3. Cooling continues to \~40°C, allowing moisture to dry and label adhesives to set. Container Types for Retorting 1. Metal Cans 2. Glass Jars/Bottles 3. Flexible Pouches 4. Rigid Trays Air Exhausting Methods Essential to reduce strain during heating and prevent oxidation. 1. Hot Filling: Pre-heats food, reducing processing time. 2. Cold Filling and Heating: Heats containers and contents with lids partially sealed. 3. Vacuum Pump: Mechanically removes air. 4. Steam Flow Closing: Blasts steam to replace air before sealing (best for liquid foods). Ultrahigh-Temperature (UHT) processing, also known as aseptic processing, is a method of sterilizing liquid foods and foods containing small or discrete particles. This process achieves commercial sterility by heating products to a high temperature for a short time and then cooling them rapidly under sterile conditions before packaging. Here are the key aspects of UHT processing, including its benefits, limitations, theory, equipment, and processing techniques: Advantages of UHT Processing 1. Extended Shelf Life: UHT-treated foods can be stored for six months or more without refrigeration. 2. Efficient Processing: Shorter processing times at high temperatures preserve nutrients and sensory qualities. 3. Independence from Container Size: Unlike traditional canning, UHT processing time is unaffected by container size. 4. Versatility: Suitable for a variety of liquid and particulate foods, such as milk, soups, and baby foods. 5. Packaging Flexibility: Use of lightweight, laminated cartons instead of metal cans reduces costs. Limitations of UHT Processing 1. High Costs: Equipment and maintenance are expensive due to the need for sterilized packaging and sterile environments. 2. Complexity: Requires skilled operators and sophisticated technology to maintain sterile conditions. 3. Enzyme Heat Resistance: Some enzymes, like proteases and lipases, may survive UHT treatment, affecting long-term product quality. Theory of UHT Processing Microbial Destruction vs. Nutrient Retention: High temperatures destroy microorganisms more effectively than nutrients, preserving food quality. Sterilization Parameters: Sterility is assessed using factors like , , and , which evaluate microbial lethality and nutrient damage. For instance: : A measure of microbial spore reduction. : A measure of chemical damage, such as nutrient loss. Heat Transfer Dynamics: Ensures all particles, even those moving fastest, achieve the required temperature and holding time for sterility. Processing Techniques 1. Direct Heating: Steam Injection: Steam rapidly heats the product; flash cooling follows to remove excess moisture. Steam Infusion: Food is sprayed into a steam chamber, heated, and cooled quickly. Suitable for heat-sensitive foods. Advantages: Rapid heating and cooling, reduced nutrient loss. Limitations: Limited to low-viscosity foods and higher energy costs. 2. Indirect Heating: Plate Heat Exchangers: Efficient energy regeneration but limited to low-viscosity foods. Tube-and-Shell Heat Exchangers: Handle higher pressures and flow rates but are less flexible and harder to inspect. Scraped Surface Heat Exchangers: Ideal for viscous or particulate foods but expensive. Equipment Characteristics Operates at temperatures above 132°C. Ensures turbulence for uniform heating. Uses pumps to maintain consistent product flow. Includes systems for continuous cleaning to prevent fouling. Classified into: Direct Systems: Steam injection or infusion. Indirect Systems: Plate or tubular heat exchangers. Alternative Systems: Microwave, ohmic, and induction heating. Advances in UHT Processing Recent innovations have addressed challenges in processing larger food particulates (up to 2.5 cm). Technologies like ohmic heating and systems such as APV Jupiter and Alfa-Laval Twintherm have improved sterilization and heat transfer control, enhancing safety and product quality. UHT processing is widely used in the food industry due to its ability to combine shelf stability with high-quality retention. However, its application requires precise control of processing conditions, tailored equipment, and advanced operator expertise. Nutritional Value of Canned and UHT Foods Canned Foods Canning involves intense heat treatment, which impacts nutrients in the following ways: Carbohydrates and Lipids: Hydrolysis occurs, but these nutrients remain bioavailable, preserving their nutritional contribution. Proteins: Coagulation happens, leading to: Amino Acid Loss: 10--20% loss, with reductions in lysine being the most notable (up to 25%). Tryptophan and methionine losses slightly reduce the biological value of proteins by 6--9%. Vitamins: Significant losses occur, particularly for: Thiamin: 50--75% loss. Pantothenic Acid: 20--35% loss. Water-Soluble Vitamins (e.g., Ascorbic Acid): Degradation depends on food type, oxygen presence, and preparation methods (e.g., peeling, blanching). In some cases, water-soluble vitamins leach into the brine or syrup, which may still be consumed, reducing the perceived nutrient loss. Positive Effects: In soy--meat products, trypsin inhibitors are reduced, which enhances nutritional quality. UHT/Aseptically Processed Foods Aseptic processing involves higher temperatures for shorter durations, which preserves nutrient quality better than canning: Proteins and Amino Acids: Minimal loss, retaining biological value. Vitamins: Thiamin and Pyridoxine: Notable losses occur. Resistant Vitamins: Riboflavin, pantothenic acid, biotin, nicotinic acid, and vitamin B6 remain intact. Other Nutrients: Lipids, carbohydrates, and minerals are virtually unaffected. Comparative Insights Canning: Results in greater nutrient losses due to prolonged heating. However, canned foods retain many nutrients and are shelf-stable for extended periods. UHT Processing: Provides superior nutrient retention, especially for heat-sensitive vitamins, making it more suitable for preserving milk, cream, and other liquid foods with minimal nutritional compromise. Note: Nutrient losses can continue during storage for both canned and UHT products, influencing their long-term dietary contribution. **EVAPORATION AND DISTILLATION** Evaporation and Distillation in Food Processing Overview: Evaporation and distillation are unit operations used to separate components in food to increase its value. Separation is achieved by exploiting the differences in vapour pressure (volatility) and using heat to remove one or more components from the bulk food. Evaporation: Definition: Evaporation is the partial removal of water from liquid foods by boiling off water vapour, increasing solids content, and preserving the food by reducing water activity. Common uses: Pre-concentrating foods (e.g., fruit juice, milk, coffee) before drying, freezing, or sterilisation. Reducing weight and volume, saving energy in subsequent operations, and reducing storage, transport, and distribution costs. Products like fruit drinks for dilution, concentrated soups, tomato or garlic pastes, and sugar. More expensive in energy consumption than other concentration methods but can achieve a higher degree of concentration. Theory of Evaporation: Heat Transfer: Sensible heat raises the temperature of the food to its boiling point. Latent heat of vaporisation supplied by steam forms bubbles of vapour, which leave the surface of the boiling liquid. The rate of evaporation depends on both the rate of heat transfer and the rate of mass transfer of vapour from the food. Energy Efficiency and Concentration: Different concentration methods have varying degrees of energy efficiency and concentration capability (e.g., evaporation, ultrafiltration, freeze concentration). Heat and Mass Balances: Mass Balance: Mass of feed entering the evaporator = mass of product and vapour removed. For water: For solutes: Total mass: Heat Balance: Heat given up by condensing steam = heat used to raise feed temperature and boil off vapour. Thermally Accelerated Short-Time Evaporator (TASTE) 1\. Overview Purpose: The TASTE evaporator is designed to rapidly concentrate liquid food products while minimizing the thermal degradation of heat-sensitive compounds, such as vitamins, flavors, and proteins. Technology: It uses a combination of high temperature and short residence time to achieve efficient evaporation without compromising the quality of the food. Design: The system operates under vacuum conditions to reduce the boiling point of water, allowing for faster evaporation at lower temperatures. 2\. Key Features Short Residence Time: One of the primary benefits of TASTE evaporators is the very short residence time of the product in the evaporator. This helps to preserve the product's sensory properties and nutritional value. High Efficiency: The TASTE system is designed for high heat transfer efficiency, allowing the liquid food to be concentrated in a short amount of time. Temperature Control: Despite the high temperatures used in the process, the system is designed to minimize heat exposure by reducing the residence time, thus preventing heat-induced damage. Vacuum Operation: Operating under a vacuum ensures that evaporation happens at lower temperatures, which helps preserve the volatile compounds in the product. 3\. Applications Juices and Concentrates: Often used in the production of fruit juices and other beverage concentrates where flavor retention is critical. Dairy Products: TASTE evaporators are also used to concentrate milk and other dairy products while minimizing nutrient losses. Flavor Preservation: Due to its design, TASTE is effective in preserving delicate aromas and flavors that are typically lost in traditional evaporation methods. 4\. Benefits Enhanced Flavor Retention: Because of the rapid evaporation process and short exposure to heat, volatile flavor compounds are retained better than in traditional evaporation techniques. Nutrient Preservation: Nutrients that are sensitive to heat, such as vitamins, are less likely to degrade in the short residence time, making it ideal for high-quality concentrates. Energy Efficiency: Compared to other evaporation methods, TASTE is more energy-efficient, as it requires less time to concentrate the liquid and achieves this with lower temperatures. 5\. Limitations Cost: The capital costs for setting up a TASTE system can be high due to the complexity of the design and equipment needed. Limited Scale: Although it works well for small to medium-scale production, it might not be as cost-effective for very large-scale evaporation needs unless highly specialized. \-\-- This should now properly capture the TASTE evaporator technology as requested. Let me know if you need any other adjustments or more details! Factors Influencing Heat Transfer: Temperature Difference: Increasing the pressure and temperature of steam or reducing the boiling liquid temperature by vacuum evaporation. Deposits on Heat Transfer Surfaces: Fouling reduces the rate of heat transfer. Denaturation of proteins and deposition of polysaccharides may cause food to burn onto hot surfaces. Boundary Films: The thickness of the liquid film on the evaporator wall can resist heat transfer. This can be reduced by promoting convection currents or turbulence. Economic Considerations: Energy Consumption: A large amount of energy is required to remove water from food by boiling (2257 kJ per kg of water evaporated). Loss of Product Quality: Losses due to foaming and entrainment, where fine mist is carried out of the evaporator with the vapour. Energy Savings: Vapour Recompression: Increasing vapour pressure and temperature using a compressor or steam jet to reuse as heating medium. Preheating: Using vapour to heat incoming feed or condensed vapour to raise steam in a boiler. Multiple Effect Evaporation: Several evaporators are connected, with vapour from one effect used as the heating medium in the next. Multiple Effect Evaporation Energy Efficiency: Multiple effect systems reuse vapour produced in one effect to heat the next effect. This reduces energy consumption, but requires progressively lower pressures for each effect to maintain the necessary temperature difference between feed and heating medium. Number of Effects: The number of effects (typically 3--6) depends on the balance between energy savings and capital costs. More than 6 effects can be used in some cases. System Arrangements: Forward Feed: Simple, inexpensive, and minimizes risk of heat damage, but the heat transfer rate decreases as the feed becomes more viscous. Reverse Feed: Uses the best steam for the most difficult material, improving heat transfer and economy. Mixed Feed: Combines simplicity and economy, especially useful for viscous foods. Parallel Feed: Ideal for crystal production, as it allows better control over crystallization. Equipment Evaporator Components: 1. Heat exchanger (calandria) to transfer heat. 2. Means of separating vapours. 3. Mechanical or steam ejector vacuum pumps to create the necessary vacuum. Types of Evaporators: Natural Circulation Evaporators: Suitable for low-viscosity, non-heat-sensitive products like syrups and fruit juices. These include open-pan evaporators, short-tube evaporators, and long-tube evaporators (climbing or falling-film). Forced Circulation Evaporators: Use pumps or scrapers to move the liquid, maintaining high heat transfer rates and short residence times. Plate evaporators and expanding-flow evaporators fall into this category, suitable for heat-sensitive, high-viscosity foods like dairy and fruit juices. Design Considerations The choice of evaporator depends on: Operating Capacity: Kilograms of water removed per hour. Degree of Concentration: Percentage of dry solids. Heat Sensitivity: Some products may require low-temperature evaporation to avoid degradation. Economic Factors: The trade-off between capital costs, energy consumption, and product quality. Energy Consumption Energy Recovery Systems: 1. Vapour Recompression: Increases vapour pressure and reuses it as heating medium. 2. Preheating: Uses condensed vapour to preheat the incoming feed liquor. 3. Multiple Effect Evaporation: Uses the vapour from one effect to heat subsequent effects, reducing steam consumption. Advantages of Evaporation Cost-effective for concentrating liquids. Allows the concentration of heat-sensitive products when operated under partial vacuum. Suitable for large-scale food processing, such as juice and milk concentration. Limitations of Evaporation Energy-intensive. Potential product losses due to fouling, foaming, or entrainment. The risk of heat damage to sensitive or high-viscosity foods. Mechanical (Agitated) Thin-Film Evaporators 1. Types: Scraped-Surface Evaporators: Film thickness up to 1.25 mm. Wiped-Surface Evaporators: Film thickness around 0.25 mm. 2. Operation: High-speed rotor with blades keeps the film agitated. Promotes high heat transfer and prevents burning of the product. Residence time adjustable (0.5 to 100 seconds) depending on the food and required concentration. 3. Suitability: Ideal for viscous, heat-sensitive foods or those prone to foaming/fouling (e.g., fruit pulps, tomato paste, dairy, honey, cocoa mass, coffee). 4. Challenges: High capital and operating costs. Limited to single-effect systems, resulting in reduced throughput and poor steam economy. 5. Centri-Therm Evaporator: Operates using centrifugal force to move the liquid across heated cones. High heat transfer coefficients and short residence times (0.6--1.6 seconds). Suitable for sensitive foods like coffee extracts, fruit juices, and meat extracts. 6. Usage: Typically used for finishing highly viscous products after initial concentration in other evaporators. Provides high-quality concentrates with minimal heat damage. Impact on Food Quality 1. Loss of Volatile Compounds: Evaporation causes loss of volatile aroma compounds, reducing flavor in products like fruit juices. Some volatiles can be recovered through vapour condensation, fractional distillation, or by using inert gases. 2. Color and Chemical Changes: Evaporation may darken the color of food due to increased concentration of solids and chemical reactions (e.g., Maillard browning). Short residence times and lower boiling temperatures minimize these effects. 3. Nutrient Retention: Proper control of evaporation conditions helps retain nutritional qualities, such as vitamins and other essential nutrients. Products like milk can retain vitamins A, D, and niacin, with minimal losses in other nutrients when carefully processed. 4. Energy Efficiency: The design of evaporators (e.g., mechanical thin-film) allows for high heat transfer and short evaporation times, making the process more energy-efficient. However, single-effect evaporators may not provide the best steam economy, especially for large-scale operations. **DEHYDRATION** Dehydration (Drying) Overview: Definition: Dehydration is the process of applying heat under controlled conditions to remove most of the water content from food through evaporation (or sublimation in freeze drying). Purpose: Extends shelf life by reducing water activity, inhibiting microbial growth and enzyme activity. Reduces weight and bulk, lowering transport and storage costs. Provides convenient, easy-to-handle ingredients for consumers or food processors. Affects eating quality and nutritional value, so minimizing these changes is crucial in equipment design. Commonly Dried Foods: Coffee, milk, raisins, fruits, pasta, flours, beans, pulses, nuts, breakfast cereals, tea, spices. Key Ingredients in Manufacturing: Egg powder, flavorings, colorings, sugars (lactose, sucrose, fructose), enzymes, yeasts. Theory of Dehydration: Basic Concept: Dehydration involves the application of heat and removal of moisture, with heat transfer driving moisture evaporation. Osmotic Dehydration: Soaking foods in concentrated sugar or salt solutions to remove water by osmotic pressure differences (used in crystallized fruits and pre-treatment for fish and vegetables). Key Factors Influencing Drying Rates: 1. Processing Conditions: Temperature, humidity, airflow. 2. Nature of the Food: Composition, structure, moisture content. 3. Dryer Design: Type of drying equipment used. Drying Using Heated Air: Psychrometrics: Study of air-water vapour systems. Three factors control drying capacity: 1. Water vapour content of air (absolute or relative humidity). 2. Air temperature. 3. Air velocity over food. Dry-Bulb & Wet-Bulb Temperature: The dry-bulb measures air temperature, while the wet-bulb measures temperature when water evaporates from the cloth. Dew Point: The temperature where air becomes saturated with moisture (100% RH). Adiabatic Cooling: A process where the absolute humidity decreases as the air temperature increases. Mechanism of Drying: Air Velocity: Faster air removes moisture more efficiently due to a thinner boundary layer, enhancing heat transfer. Drying Phases: 1. Constant-Rate Period: Water moves from food's interior to the surface, maintaining the surface at the wet-bulb temperature. 2. Falling-Rate Period: After the critical moisture content is reached, moisture from the interior diffuses to the surface and evaporates at a slower rate, causing drying to decelerate. Drying Phases: 1. Constant-Rate Period: Water evaporates from the surface, keeping the surface temperature close to the wet-bulb temperature of the air. 2. Falling-Rate Period: Once the moisture falls below the critical level, drying slows as internal moisture diffuses to the surface. The surface temperature rises towards the dry-bulb temperature. Factors Influencing Drying Rate: Food Composition & Structure: Orientation of fibers and cell structure affects moisture movement. Moisture is removed more easily from intercellular spaces. Food Size: Smaller pieces dry faster due to larger surface areas and shorter moisture travel distances. Drying Conditions: The speed of airflow, temperature, and humidity levels directly impact drying efficiency. Other Drying Methods: Microwave, Dielectric, and Radiant Drying: Described in other chapters. Freeze Drying: Sublimation process covered separately. Equipment and Systems: Hot-Air Dryers: Optimized to reduce heat loss with insulation, air recirculation, heat exchangers, and low nitrogen oxide burners for better energy efficiency. Bin Dryers: Large cylindrical or rectangular containers with mesh bases. Air passes up through food, suitable for "finishing" drying in low air velocity conditions. Cabinet Dryers: Insulated cabinets with shallow trays that circulate heated air to ensure uniform drying. Energy Efficiency: Energy Consumption: Energy consumption varies based on the drying method, with fluidized-bed and spray drying being more energy-intensive than other methods. Measures to reduce energy use include heat recovery and optimizing dryer design. Drum Dryers (Roller Dryers) Drum dryers are used to dry food by applying it to rotating hollow steel drums that are heated internally by pressurized steam at temperatures between 120--170ºC. The food is spread onto the drum's outer surface using dipping, spraying, spreading, or auxiliary feed rollers. The dried food is scraped off by a doctor blade before the drum completes one full rotation. Types: Drum dryers may have a single drum, double drums, or twin drums. The single-drum configuration is the most commonly used, offering flexibility, easier maintenance, and greater surface area for drying. This setup avoids the risk of damage from foreign objects falling between the drums. Applications: Drum drying is suitable for drying slurries with larger particles, such as potato flakes, pre-cooked cereals, molasses, some dried soups, fruit purees, and whey or distillers' solubles for animal feed. It is more suitable than spray drying for such products due to its high drying rates and energy efficiency. Challenges: Drum drying is less favorable for sensitive foods because high temperatures can cause heat damage. The high capital cost of the machinery also limits its use in large-scale production compared to other methods, such as spray drying. Developments: Recent technological advancements include the use of auxiliary rolls to remove and reapply food during drying, high-velocity air to increase drying rates, and chilled air to cool products. Vacuum chambers are sometimes used to lower drying temperatures, though this system has high capital costs and is primarily used for heat-sensitive foods. Vacuum Band and Vacuum Shelf Dryers Vacuum Band Dryers: Food slurry is spread or sprayed onto a steel band, which passes over steam-heated drums and radiant heaters within a vacuum chamber (at 1--70 Torr). The food is dried by the first steam-heated drum, then further dried by steam-heated coils or radiant heaters. The dried food is cooled by a second water-cooled drum and removed by a doctor blade. Vacuum Shelf Dryers: These consist of hollow shelves in a vacuum chamber where food is placed in thin layers on metal trays. A partial vacuum is drawn, and steam or hot water passes through the shelves to dry the food. Advantages: Both methods are especially suitable for heat-sensitive foods because they minimize heat damage during the drying process. They are commonly used to produce puff-dried foods. Challenges: One challenge with both methods is shrinkage, which reduces the contact between the food and the heated surfaces. They also have relatively high capital and operating costs and lower production rates compared to other drying methods. Explosion Puff Drying Explosion puff drying involves partially drying the food to a moderate moisture content and then sealing it in a pressure chamber. The temperature and pressure are increased, and once they are rapidly released, the food expands, creating a fine porous structure. This structure allows faster final drying and better rehydration. Applications: Initially used for breakfast cereals, explosion puff drying is now applied to various fruit and vegetable products. Benefits: This method preserves sensory and nutritional qualities and facilitates faster rehydration of the dried food. Effects on Food Texture Changes: Shrinkage & Toughness: During drying, moisture loss causes cell walls to collapse, leading to shrinkage, cracks, and a shriveled appearance. Drying at high temperatures can cause the food to become tough (e.g., meat). Case Hardening: High drying temperatures lead to a hard surface that traps moisture inside. This slows down further drying and creates a food product with a dry exterior but moist interior. Starch Gelatinization & Protein Denaturation: Starch may gelatinize, and proteins can denature during drying, altering the texture of foods like vegetables, fruits, and meats. Effect on Powders: In powdered foods, bulk density, wettability, and dispersibility are affected by particle size, structure (hollow or solid), and drying conditions. Nutritional Changes: Vitamins: Heat-sensitive vitamins (e.g., Vitamin C, Thiamine) are lost during drying, especially if high temperatures are used. The degree of loss depends on drying time, temperature, and exposure to oxygen. Fat-Soluble Nutrients: Vitamins A, D, E, and K are not significantly concentrated during drying. However, oxidation of unsaturated fats can lead to nutrient loss, particularly if food is stored improperly (e.g., in high temperatures or oxygen exposure). Proteins: Drying processes, especially drum drying, can partially denature proteins, affecting their solubility and biological value. Milk proteins, for example, lose solubility and clotting ability, which can affect the final product's quality. Color and Flavor: Color Loss: Heat can cause pigment changes, such as browning of carotenoids and chlorophyll. Oxidation and residual polyphenol oxidase activity in fruits lead to browning, which can be prevented with blanching or sulfur dioxide. Flavor Loss: Volatile compounds responsible for flavor are often lost during drying, especially at high temperatures. This can result in a decrease in the flavor of foods, particularly fruits, herbs, and spices. Oxidation: Oxygen exposure during storage can further degrade the flavor by oxidizing volatile compounds or fats, leading to rancidity in milk, oils, and other foods containing lipids. \-\-- Rehydration Water Absorption: Texture Recovery: Rehydrated foods often don\'t regain their original texture. The breakdown of cell structure during drying makes it difficult for the food to fully recover its pre-dried texture. Changes in Texture: Foods such as fruits and vegetables tend to soften upon rehydration, but they may remain less firm than fresh foods due to cellular damage during drying. Starch & Protein Alteration: Heat during drying reduces the elasticity of starch and proteins, making it difficult for the food to retain its original texture when rehydrated. Rehydration Time: Faster Rehydration: Foods that are dried rapidly (e.g., spray-dried powders) tend to rehydrate more easily due to smaller particle sizes and a more porous structure. Impact of Drying Method: Foods dried at lower temperatures or slower drying rates often rehydrate more effectively, maintaining better texture and quality. Shrinkage Effects: Dried foods with high shrinkage, like some fruits and meats, may take longer to rehydrate and not recover the original structure. Nutritional Impact: Water-Soluble Nutrients: Rehydration can restore some of the water-soluble nutrients (like Vitamin C) that were lost during drying. However, some nutrient loss may still occur during storage. Fat-Soluble Nutrients: While these nutrients (e.g., Vitamins A and E) are not lost during drying, they may degrade slightly if exposed to heat or oxidation during storage. **FRYING** Purpose: Frying alters the eating quality of food and has a secondary preservative effect due to thermal destruction of microorganisms, enzymes, and reduced water activity. Shelf life of fried foods depends on moisture content after frying. Foods that retain moisture (e.g., doughnuts, fish, poultry) have a shorter shelf life, while foods like potato chips, maize snacks, and thoroughly dried fried items can last up to 12 months at ambient temperature with proper packaging. Theory: When food is placed in hot oil, the surface temperature rises, causing water to vaporize as steam, drying the surface. A crust forms as the oil temperature rises to match the food's surface temperature. Internal temperatures rise more slowly toward 100ºC. The heat transfer rate depends on the temperature difference between oil and food, and the surface heat transfer coefficient, with food type and oil viscosity influencing this process. The frying process Involves the formation of a porous crust, with water vapor pressure gradients driving moisture loss. Frying time depends on food type, oil temperature, frying method, thickness, and desired eating quality. Frying Temperatures: High temperatures (180--200ºC) reduce processing time but cause oil deterioration and require more frequent oil changes. Foods requiring a moist interior are fried at high temperatures. Low temperatures are used for foods that require drying, with slower evaporation to prevent excessive surface color and flavor changes. Methods: 1. Shallow (Contact) Frying: Best for foods with a large surface-area-to-volume ratio (e.g., bacon, eggs, burgers). Heat transfer is mainly by conduction from the pan's hot surface through a thin oil layer. Results in irregular browning due to varying oil layer thickness. 2. Deep-Fat Frying: Involves convection within the hot oil and conduction to the food interior, ensuring uniform heat treatment. Irregularly shaped food may absorb more oil after frying. Heat transfer increases significantly due to steam escaping, but excessive evaporation can reduce heat transfer efficiency. Equipment: Shallow-frying equipment: Consists of a heated metal surface with a thin layer of oil. Continuous deep-fat fryers: Food is suspended in hot oil via a conveyor system, ensuring consistent frying. Oil is continuously recirculated and filtered to maintain quality. Effect on Foods: Frying impacts both oil quality and food characteristics. Prolonged heating of oil can cause oxidation, producing volatile and non-volatile decomposition products that affect flavor and color, but also contribute to the desired fried flavor. Nutrient losses in fried foods depend on frying temperature and oil conditions. Rapid crust formation at high temperatures helps retain nutrients in the food, but extended frying to dry the food leads to higher losses, particularly fat-soluble vitamins like Vitamin E. Health Considerations: Excessive oil absorption can increase fat content, contributing to health risks like obesity and coronary heart disease. There is a growing trend towards reducing oil absorption in fried foods to meet consumer demands for lower-fat products. **\ ** **FREEZING** Freezing in Food Processing Overview of Freezing Freezing is a process where the temperature of food is reduced below its freezing point, causing a portion of the water to freeze into ice crystals. This reduces water activity (aw) by immobilizing water as ice, which helps preserve food by lowering water activity and, in some cases, pre-treating foods with blanching. When done correctly, freezing has minimal impact on the nutritional or sensory qualities of food. Commercially Frozen Food Groups The main categories of frozen foods include: Fruits: Strawberries, oranges, raspberries, blackcurrants (whole, pureed, or as juice concentrates) Vegetables: Peas, green beans, sweetcorn, spinach, sprouts, potatoes Fish & Seafood: Cod, plaice, shrimps, crab meat, fish fillets, fish cakes, fish fingers, prepared dishes Meats: Beef, lamb, poultry (as carcasses, joints, cubes, sausages, burgers, reformed steaks) Baked Goods: Bread, cakes, pies (fruit and meat) Prepared Foods: Pizzas, desserts, ice cream, ready-to-eat meals Market Trends The rise in frozen food consumption is linked to increased domestic freezer ownership and microwave ovens. Frozen and chilled foods are perceived as fresh and high-quality, often surpassing canned or dried alternatives in the market, particularly in meat, fruit, and vegetable sectors. However, distribution costs remain high due to the need to maintain low temperatures. Recent innovations like using carbon dioxide "snow" in transport allow more flexibility in temperature management and enable mixed-temperature loads in vehicles. Theory of Freezing During freezing, sensible heat is removed first to lower the temperature to the freezing point, and in fresh foods, heat from respiration is also removed. This heat load determines the size of freezing equipment needed. Most foods have a high water content, requiring significant energy to remove latent heat, form ice crystals, and freeze the food. Refrigerants in mechanical freezing systems or cryogens are used for energy supply. Freezing Curve Components When monitoring temperature at the thermal center of the food, the freezing process follows a characteristic curve: 1. AS: The temperature drops below the freezing point, but water remains liquid, a phenomenon called supercooling (can be up to 10°C below freezing point). 2. SB: Ice crystals form, releasing latent heat and causing the temperature to rise to the freezing point. 3. BC: Latent heat is removed as ice forms, and the temperature remains constant. The freezing point is depressed as solute concentration increases in the unfrozen portion, causing a slight temperature drop. 4. CD: Supersaturation of a solute causes it to crystallize, releasing latent heat and raising the temperature to the eutectic temperature of the solute. This freezing curve helps understand the various stages of freezing and the energy required for the process. Freezing Process: Continued Freezing Time and Temperature Changes (Fig. 21.1) DE: The crystallization of water and solutes continues. The total freezing time, or freezing plateau, is determined by the rate at which heat is removed. EF: The temperature drops to match the freezer temperature. A proportion of the water remains unfrozen at commercial freezing temperatures, depending on the food type and storage temperature. For example, at -20°C storage, water frozen percentages are 88% in lamb, 91% in fish, and 93% in egg albumin. Ice Crystal Formation Before ice crystals form, water molecules must nucleate, either through homogeneous nucleation (random molecular combinations) or heterogeneous nucleation (nucleation around suspended particles or cell walls). Heterogeneous nucleation is more common in foods and occurs during supercooling. Fast freezing results in many small ice crystals due to the rapid formation of nuclei. Freezing rate influences both the number and size of ice crystals, with faster freezing resulting in more but smaller crystals. Growth of Ice Crystals Ice crystal growth is primarily influenced by the heat transfer rate during most of the freezing plateau. However, once solute concentration increases as the freezing process progresses, the mass transfer rate (movement of water and solutes) starts to influence growth toward the end of freezing. Solute Concentration As freezing progresses, the concentration of solutes in the unfrozen portion increases, affecting pH, viscosity, surface tension, and redox potential. Each solute has its eutectic temperature (the temperature at which it crystallizes), but due to the complexity of food compositions, a "final eutectic temperature" is used. Below this temperature, the food's solutes become "glass-like," which helps preserve texture and stability at low storage temperatures. However, some foods like fruits, with low glass transition temperatures, can experience texture damage during frozen storage. Volume Changes Freezing causes a 9% increase in volume due to ice expansion. However, the degree of expansion varies depending on: Moisture content: Higher moisture contents result in greater volume changes. Cell structure: Foods like plant materials have intercellular air spaces that can absorb volume changes. For example, whole strawberries expand by 3% when frozen to -20°C, while ground strawberries expand by 8.2%. Solute concentration: Higher solute concentrations lower the freezing point and reduce expansion. Freezing temperature: Determines the amount of unfrozen water and degree of expansion. Crystallized components: Ice, fats, and solutes contract upon cooling, which reduces volume. Rapid freezing leads to crust formation, which prevents further expansion and causes internal stresses, making food more susceptible to cracking, especially when impacted during freezing. Freezing Time Calculation Freezing time is influenced by several factors: Thermal conductivity of the food Surface area for heat transfer Distance heat must travel (size of food pieces) Temperature difference between food and freezing medium Insulating effect of any boundary film (like air or packaging) Freezing Time Approaches 1. Effective Freezing Time: Measures the time food spends in the freezer and is used for calculating manufacturing throughput. 2. Nominal Freezing Time: Provides an estimate of potential product damage but doesn't consider initial conditions or cooling rates at different points on the food. Challenges in Freezing Time Calculation Accurately calculating freezing time is complex due to: Variations in initial temperature, size, and shape of food pieces Differences in freezing points and ice formation rates within the food Changes in food properties like density, conductivity, and heat capacity as temperature decreases Latent heat removal complicates heat transfer calculations, making precise freezing rate determination challenging. Practical solutions for calculating freezing times often rely on simplified formulas (such as those developed by Plank) under assumptions like starting with all unfrozen water at its freezing point. Freezing Time and Thermal Conditions Freezing Time Definition The time required to lower the temperature of food from its initial value to a pre-determined final temperature at the thermal center is referred to as freezing time. This process is crucial for ensuring that the food reaches the desired temperature for preservation. Thermal Centre and Freezing Front The thermal centre of the food is the point that cools most slowly and is typically used for determining freezing time. The time it takes for the surface of the food to reach 0ºC, and for the thermal centre to reach 10ºC below the first ice formation temperature, is an important parameter in freezing time calculations. Assumptions for Steady-State Heat Transfer Certain conditions are assumed for steady-state heat transfer during freezing: 1. Steady-State Conditions: Heat transfer occurs slowly enough that steady-state conditions can be applied, meaning the rate of heat removal remains constant. 2. Freezing Front Shape: The freezing front (the boundary between frozen and unfrozen food) maintains a similar shape to the food itself. For instance, if the food is a rectangular block, the freezing front remains rectangular. 3. Single Freezing Point: The food is assumed to have a single freezing point. 4. Constant Density: The density of the food is assumed to remain unchanged throughout the freezing process. 5. Thermal Properties: The thermal conductivity and specific heat of the food are considered constant in the unfrozen state. Once the food reaches the frozen state, these properties change to a different constant value. These assumptions help simplify calculations and models of freezing time, allowing for more predictable results during the freezing process. Freezing Equipment Selection When selecting freezing equipment, the following factors must be considered: Freezing Rate: The required speed at which food must be frozen. Food Characteristics: The size, shape, and packaging requirements of the food. Operation Type: Whether the operation is batch or continuous. Scale of Production: The amount of food to be processed. Product Range: The variety of products to be frozen. Cost: Both capital and operational costs. Types of Freezers 1. Mechanical Refrigerators These use a refrigerant that is continuously evaporated and compressed in a cycle to cool air, liquid, or surfaces that remove heat from food. This is a common method in many freezing operations. 2. Cryogenic Freezers These use solid or liquid carbon dioxide, liquid nitrogen, or previously liquid Freon, which comes into direct contact with food to rapidly freeze it. Cryogenic freezing is particularly fast and efficient for certain types of products. 3. Insulation Materials Freezing equipment is insulated using materials like expanded polystyrene, polyurethane, or others that have low thermal conductivity to maintain freezing temperatures. 4. Computer Control Most freezing equipment now incorporates advanced computer controls to monitor various process parameters, display trends, detect faults, and adjust conditions for optimal freezing. Cooled-Air Freezers 1. Chest Freezers Used in stationary (natural-circulation) air at temperatures between -20ºC and -30ºC. They are not ideal for commercial freezing because of slow freezing rates (taking 3--72 hours), which affects product quality and process efficiency. Common uses include freezing carcass meat, storing pre-frozen products, and hardening ice cream. 2. Cold Stores Often used for storing frozen products and freezing carcass meat. They suffer from problems such as ice formation on surfaces due to moisture in the air or from unpackaged foods. This ice reduces efficiency, wastes energy, and can create safety hazards. Desiccant dehumidifiers can help reduce moisture in the air, improve refrigeration efficiency, and reduce the need for frequent defrosting. 3. Blast Freezers Air is recirculated over food at temperatures between -30ºC and -40ºC at speeds of 1.5--6.0 m/s. High air velocity reduces the thickness of the boundary films surrounding the food, improving heat transfer efficiency and decreasing freezing time. Can be either batch (food stacked on trays) or continuous (food on trolleys or conveyor belts). Multi-pass tunnels use several belts to further break up clumps of food and ensure even freezing. Challenges with Cooled-Air Freezing Ice Formation: Air moisture can cause ice to form on floors, walls, and evaporator coils, reducing freezer efficiency and increasing energy usage. Energy Loss: Ice formation takes up energy that would otherwise be used to cool the space, thus affecting cost efficiency. Operational Hazards: Ice accumulation can create slippery surfaces and lead to potential accidents. By considering these factors and types of equipment, freezing operations can be optimized for efficiency, quality, and cost-effectiveness. Freezing Equipment Types 1. Belt Freezers (Spiral Freezers) Structure: Belt freezers feature a continuous flexible mesh belt arranged into spiral tiers that carry food through a refrigerated chamber. Self-Stacking Design: Some designs feature a self-stacking belt, where each tier rests on the vertical sides of the tier below, eliminating the need for support rails and improving capacity by up to 50%. Airflow: Cold air or liquid nitrogen is directed in a countercurrent flow through the belt stack, reducing moisture evaporation and weight loss. Capacity: Belt freezers are compact and have high capacities, with some models processing up to 3,000 kg/h. They are suitable for a wide range of products such as pizzas, cakes, ice cream, fish, and chicken. Advantages: Low maintenance costs, automatic loading/unloading, and flexibility in freezing various food types. 2. Fluidised-Bed Freezers Structure: Modified blast freezers where air at temperatures between -25ºC and -35ºC is passed at high velocity (2--6 m/s) through a bed of food, typically between 2--13 cm in depth. Glaze Formation: Some designs involve two stages. The initial stage creates a thin ice glaze on the food, which prevents clumping, particularly useful for fruit and small particulate foods. Food Types: Suitable for particulate foods like peas, shrimp, and French fries, as well as through-flow freezers for larger items like fish fillets. Advantages: Higher heat transfer coefficients, shorter freezing times, and minimal dehydration of unpackaged food. The equipment is compact with high capacity. 3. Cooled-Liquid Freezers Structure: In immersion freezers, packaged food is submerged in a refrigerated liquid (such as propylene glycol, brine, or glycerol) that remains fluid throughout the freezing process. Heat Transfer: These systems offer high rates of heat transfer and relatively low capital costs. They are commonly used for products like concentrated orange juice and pre-freezing poultry. 4. Cooled-Surface Freezers Plate Freezers: These consist of stacks of hollow plates through which refrigerant is pumped at -40ºC. Foods (such as fillets or beefburgers) are placed between plates under slight pressure to improve heat transfer. Production Rates: Range from 90 to 2,700 kg/h depending on batch, semi-continuous, or continuous operation. Advantages: High heat transfer rates, good space utilization, and low operating costs. Minimal dehydration and defrosting requirements. Disadvantages: High capital costs and restrictions on the types of food that can be frozen (must be flat and thin). Scraped-Surface Freezers: Used for semi-solid or liquid foods like ice cream, these freezers scrape frozen product off the walls of the freezer barrel and simultaneously incorporate air, creating a smooth, creamy texture. Freezing Speed: Very fast, freezing up to 50% of the water in a few seconds, resulting in very small ice crystals for a smooth texture. 5. Cryogenic Freezers Structure: Cryogenic freezers use refrigerants like liquid nitrogen or carbon dioxide, which change state (from liquid to gas or solid to gas) as they absorb heat from the food. The cryogen is in direct contact with the food for rapid freezing. Refrigerants: Liquid Nitrogen: 48% of the freezing capacity comes from the latent heat of vaporization, with the remaining 52% from the cold gas, which is recirculated for efficiency. Carbon Dioxide: A lower enthalpy than liquid nitrogen, but the majority of the freezing capacity comes from the sublimation of solid CO₂. It's less harsh on the food due to its lower boiling point and is bacteriostatic. Advantages: Cryogenic freezers offer low capital costs and flexibility, allowing the freezing of various products without major system adjustments. Safety: Carbon dioxide is toxic and should be properly vented to avoid harm to operators. Its consumption rate is higher than liquid nitrogen but with lower storage losses. Summary of Key Benefits: Belt Freezers: High capacity, space-efficient, flexible, low maintenance. Fluidised-Bed Freezers: Rapid freezing, minimal dehydration, suitable for particulate foods. Cooled-Liquid Freezers: Low capital costs, high heat transfer rates, suitable for liquid foods. Cooled-Surface Freezers: Efficient for flat, thin foods with low operating costs. Cryogenic Freezers: Rapid freezing, flexibility, lower capital cost, but require proper handling of cryogens. These various freezing methods are selected based on product type, required freezing speed, and operational efficiency. Liquid-Nitrogen Freezers Structure and Operation: In liquid-nitrogen freezers, packaged or unpackaged food travels on a perforated belt through a tunnel where it is frozen by sprays of liquid nitrogen and by gaseous nitrogen. The production rates range from 45 to 1,550 kg/h. Freezing Process: Food may be frozen to the desired storage temperature (between -18ºC and -30ºC) before removal, or passed to a mechanical freezer to complete the process. The use of gaseous nitrogen helps reduce thermal shock to the food, and recirculation fans increase heat transfer rates. Newer Designs: Some tunnel designs use fans beneath the conveyor to create gas vortices, which have been shown to: Double output for the same length of freezer, Reduce nitrogen consumption by 20%, Decrease dehydration by 60%. Microprocessor Control: Temperature and belt speed are controlled by microprocessors to maintain the desired exit temperature, regardless of the heat load of incoming food, providing greater flexibility and efficiency compared to mechanical systems. Advantages of Liquid-Nitrogen Freezers: Simple continuous operation, Low capital costs (about 30% of mechanical systems), Minimal dehydration (0.5% compared to 1.0--8.0% in air-blast freezers), Rapid freezing with minimal changes to sensory and nutritional quality, Exclusion of oxygen during freezing, Rapid startup and no defrost time, Low power consumption. Disadvantages: High cost of refrigerants (liquid nitrogen and carbon dioxide). Additional Uses: Liquid nitrogen is also used in spiral freezers, high-speed slicing of meat, surface hardening of ice cream, and crust formation on fragile products like seafood or sliced mushrooms before completing freezing in mechanical or cryogenic freezers. Immersion Freezing: Process: Immersion of food in liquid nitrogen leads to no weight loss but may cause high thermal shock, which can result in cracks or splits in some food types. However, this is acceptable for foods like raspberries, shrimp, and diced meat, where the rapid freezing rate yields high production of IQF foods. Effects of Freezing on Food Cellular Damage: The primary effect of freezing is the damage caused by ice crystal growth. This is especially noticeable in plant tissues, where rigid cell structures can be damaged by larger ice crystals. Animal tissues, particularly meats, are more flexible and typically handle freezing better, with less texture damage. Freezing Rate: Slow Freezing: Larger ice crystals form in intercellular spaces, causing cell walls to rupture and leading to dehydration and irreversible damage. When thawed, the food's texture is softened, and "drip loss" occurs as cellular material leaks from ruptured cells. Fast Freezing: Smaller ice crystals form inside cells and intercellular spaces, causing minimal damage. This helps retain the food's texture, though very high freezing rates may cause internal stresses resulting in cracks or splits. Impact on Food Types: Meats: The fibrous structure remains relatively intact, and the texture is usually unaffected. Fruits and Vegetables: Slow freezing causes significant damage due to large ice crystal formation, whereas fast freezing minimizes damage and helps preserve texture. In conclusion, fast freezing methods like liquid nitrogen freezing are crucial for preserving the texture and quality of food, especially for fruits, vegetables, and delicate items that are prone to damage from slower freezing processes. This section provides an in-depth look at freezing and frozen storage's effects on food, with a focus on how rapid freezing, storage temperatures, and thawing methods influence food quality. Effects of Freezing on Food Ice Crystal Growth: The primary damage caused by freezing is from the growth of ice crystals. In animal products (like meat), the fibrous structure can withstand freezing better, while in plant products, the more rigid cell structure can rupture due to ice crystal formation. Rate of Freezing: Fast freezing creates smaller ice crystals, which causes less damage and preserves texture better. Slow freezing leads to larger crystals, resulting in greater damage, especially in plant tissues. Enzyme Activity: Freezing does not activate enzymes, but in some foods, enzyme activity may cause degradation over time. For example, in vegetables, inadequate blanching before freezing allows polyphenoloxidase to cause browning. Similarly, proteolytic and lipolytic enzymes in meat can alter flavor and texture over extended storage. Changes During Frozen Storage Microbial and Biochemical Changes: The lower the temperature of frozen storage, the slower the rate of microbial and biochemical changes. However, some microorganisms (like yeast and mold) are more sensitive to higher temperatures, while others (like bacterial spores) are unaffected by freezing. Loss of Nutrients: Vitamins, especially water-soluble ones like vitamin C, degrade during frozen storage. For example, vegetables can lose up to 52% of vitamin C over 12 months at -18°C. Lipids and Oxidation: Lipid oxidation leads to off-odors and off-flavors in frozen foods, though this process is slower at lower temperatures. Freezer Burn: Temperature fluctuations during storage can cause freezer burn, which is visible as a lighter color and loss of texture due to dehydration and the formation of ice crystals at the surface of the food. Recrystallization in Freezing Types of Recrystallization: Three types of recrystallization affect frozen foods: Isomass: Changes the shape of ice crystals, reducing their surface-area-to-volume ratio. Accretive: Smaller ice crystals merge to form larger ones, reducing the number of crystals. Migratory: Smaller crystals grow larger at the expense of smaller ones, typically due to temperature fluctuations, leading to the loss of food quality. Storage Life Definitions of Storage Life: The shelf life of frozen foods can vary based on temperature fluctuations and packaging. Practical Storage Life (PSL) refers to the time until food quality significantly deteriorates, while High-Quality Life (HQL) describes the period before the food is no longer perceived as of high quality. Factors Affecting Shelf Life: Packaging, temperature stability, and pre-freezing treatments play crucial roles in preserving the quality and extending the shelf life of frozen foods. Thawing Process Challenges of Thawing: Thawing is slower than freezing due to the insulating effect of the water layer that forms as ice melts. The thawing process leads to drip losses (especially in meats and fruits) that cause the loss of water-soluble nutrients, like vitamins. Temperature and Thawing Methods: Thawing can lead to microbial growth and spoilage if done improperly. Methods like microwave or vacuum thawing avoid the issues associated with thawing in air or water. This section also discusses commercial practices to minimize quality loss during freezing and storage, emphasizing the importance of accurate temperature control and packaging. Freeze-drying and Freeze-concentration Freeze-drying and freeze-concentration are advanced preservation methods that reduce water activity without using heat, thus retaining nutritional qualities and sensory characteristics better than conventional drying or concentration methods. While these techniques result in higher quality, they come with significant costs due to the need for refrigeration and a high vacuum in freeze-drying. Freeze-drying is particularly useful for preserving delicate foods like coffee, mushrooms, herbs, and military rations, as well as microbial cultures. Freeze-concentration is less common but has applications in beverages, vinegar, and alcohol. Freeze-drying Process 1. Freezing: The food is frozen to form ice crystals, which should be small for minimal damage to the structure. Liquid foods are frozen slowly to create a lattice of ice crystals. 2. Sublimation: The primary drying stage involves sublimation, where the ice is converted directly into vapor without melting, under low pressure (below 4.58 Torr). Heat, either from conduction or microwaves, drives this process. 3. Desorption: After sublimation to about 15% moisture, the food undergoes further drying to reduce moisture to about 2% through evaporative drying. Challenges in freeze-drying include the formation of a glassy state in some liquids, which can complicate the vapor transfer. Methods like vacuum-puff freeze-drying or grinding frozen juice into granules are used to improve drying efficiency. Heat Transfer in Freeze-drying 1. Conduction: Heat is transferred through the frozen layer, and as the ice sublimates, the rate of heat transfer increases. The process is slow, especially for thicker layers of food. 2. Radiation: In radiation freeze-drying, infrared heat is applied to thin layers, allowing for more uniform and faster drying. 3. Microwave: Heat is generated at the ice front by microwaves, avoiding the need for conduction but requiring careful control to avoid overheating. Mass Transfer During Freeze-drying The rate of sublimation and moisture transfer is controlled by several factors, including the temperature of the ice, pressure in the chamber, and the condenser temperature. As drying progresses, the moisture content in the food decreases, and vapor moves from the sublimation front to the condenser, where it is frozen. Freeze-drying Equipment Freeze-dryers consist of vacuum chambers with trays to hold food, heaters to supply latent heat, refrigeration coils to condense water vapor, and vacuum pumps. The dryers can operate in batch or continuous modes. Batch systems dry food in sealed chambers, while continuous systems move trays through various heating zones. Effects on Foods Freeze-dried foods retain sensory characteristics and nutritional value better than other methods, with aroma retention of up to 100%. The texture remains intact, with little shrinkage or case hardening. However, the open porous structure can make the food fragile, requiring careful packaging in inert gases to prevent oxidative deterioration. Nutrient losses are minimal, with moderate reductions in thiamine and vitamin C. Freeze-concentration In freeze-concentration, water is crystallized into ice and separated from the liquid, achieving concentration without altering the other components significantly. This process retains volatile aroma compounds better than heat-based methods. However, freeze-concentration has high refrigeration and capital costs and is mainly used for high-value products like juices and extracts. Conclusion Both freeze-drying and freeze-concentration offer high-quality preservation with minimal nutrient loss, making them suitable for premium foods and long-term storage, despite their high energy and equipment costs. **PACKAGING** Notes on Packaging in Food Processing Importance of Packaging: Packaging plays a crucial role in food processing, especially in operations like canning and Modified Atmosphere Packaging (MAP). It helps in reducing costs and supports the development of new and minimally processed foods. Packaging is defined both in terms of its protective function (securing products for delivery) and its business role (optimizing costs and maximizing profits). Functions of Packaging: 1. Containment: To securely hold and protect contents until use. 2. Protection: Guards against mechanical damage and environmental hazards during distribution and use. 3. Communication: Provides product identification, sales assistance, handling instructions, and usage directions. 4. Machinability: Should perform well on high-speed production lines (e.g., 1000 packs per minute). 5. Convenience: Includes easy opening, dispensing, and reusability in retail containers. Marketing Considerations: Brand Image: Packaging should align with the brand's identity. Flexibility: Ability to change size and design. Compatibility: With handling, distribution, and retailer requirements. Aesthetics: Should be visually appealing, functional, and easy to dispose of or recycle. Advertising Considerations (SCIDASL): 1. Standout: Ability to attract attention among many competing products. 2. Content Identification: Clear labeling. 3. Imagery: Visual representation of the product. 4. Distinctiveness: Creating a unique product identity. 5. Adaptability: Ability to adapt to different markets. 6. Suitability: Packaging must meet product requirements. 7. Legality: Compliance with regulations. Types of Packaging: 1. Shipping Containers: Primarily for transport and protection during distribution, without a marketing function. Examples include corrugated cases, barrels, crates, and Intermediate Bulk Containers (IBCs). IBCs are used for powders and liquids and are replacing older containers like wooden crates. Features: Efficient filling, sealing, ease of handling, and minimum cost. 2. Retail Containers: Protect and advertise food in convenient quantities for sale to consumers. Examples include cans, glass bottles, plastic tubs, and flexible bags. Factors Influencing Packaging Design: Climatic Influences: Packaging must protect against UV light, moisture, oxygen, and temperature fluctuations. Contamination Prevention: Protection from microorganisms, insects, and dirt. Mechanical Protection: Resistance to damage like crushing, abrasion, or puncturing during handling and transport. Pilferage Prevention: Packaging should be tamper-evident. Barrier Properties of Packaging: 1. Light: Some foods, like those sensitive to oxidation, require packaging that restricts light (e.g., UV light). 2. Heat: Packaging materials with low thermal conductivity (e.g., polystyrene) reduce heat transfer. Insulation and heat resistance are critical for products that require sterilization or microwave heating. 3. Moisture and Gases: Packaging should control moisture and gas exchange to prevent spoilage or drying out of products. This includes maintaining water activity and ensuring oxygen, CO2, and humidity control for products like frozen foods and MAP-packaged items. Packaging Materials: Glass and Metal: Impermeable to gases and moisture, providing excellent protection against contamination and degradation. Plastic Films: Vary in permeability to gases and moisture, which can be customized based on the food's needs (e.g., low permeability for dehydrated foods). Composite Materials: Use of multilayer materials and combinations of paper, plastic, and metal for added protection and efficiency. Shelf Life and Packaging: The shelf life of packaged foods depends on the interaction between the food's moisture content, water activity, and the barrier properties of the packaging. Methods for calculating shelf life include considering permeability rates for water vapor and gases through the packaging material. Microbial and Insect Contamination Prevention: Packaging must protect food from contamination during transport and storage. Some materials, like metals and glass, naturally offer protection against microorganisms and insects. However, the sealing process must be reliable to prevent contamination at weak points like seals or closures. Mechanical Strength of Packaging: Packaging materials must withstand various mechanical forces (crushing, puncturing, vibration) during transport and handling. The strength of materials can be tested for factors like tensile strength, impact strength, and elongation, ensuring the package performs its protective role effectively. Summary: Packaging in food processing involves careful consideration of materials, functionality, and protection mechanisms to maintain food quality, extend shelf life, and support marketing efforts. Proper packaging ensures that food products are safely transported, stored, and displayed, while also complying with regulatory and consumer needs. The text you've shared covers a variety of materials used for packaging and their properties. Here's a summary of key points: Polymer Films: The properties of polymer films depend on the temperature and time the force is applied (Briston and Katan, 1974a). Films made from polymers like polyethylene, polypropylene, polyethylene terephthalate, and polystyrene are often uniaxially or biaxially oriented to improve mechanical properties. Mechanical properties of films are measured in both the axial (machine) and lateral (transverse) directions, as described by Jasse (1986). Textiles and Wood: Textile Containers: Poor gas and moisture barrier properties, not suitable for high-speed filling, and poor resistance to insects and microorganisms. Used for shipping or niche markets. Wooden Containers: Historically used for food products like fruits, vegetables, and wines. They offer good protection and stacking characteristics, but are often replaced by plastic containers, except for specific cases like wine storage. Metals: Metal Cans: Provide good protection for contents, especially under high and low temperatures. However, they are costly, heavier than plastic, and incur higher transport costs. Three-Piece Cans: Made from mild steel and coated with tin. Various lacquers like epoxy-phenolic, vinyl, and phenolic are used to prevent interaction with foods. Two-Piece Cans: Aluminum cans that are more cost-effective and have better integrity than three-piece cans. They are made through draw-and-wall-iron (DWI) or draw-and-redraw (DRD) processes. Aerosol Cans: Made from lacquered tinplate or aluminum, with a valve that dispenses products under pressure. The cans must be able to withstand pressures higher than the maximum vapor pressure of the contents. Aluminum Packaging: Properties: Lightweight, resistant to moisture, gases, and light, and offers good dead-folding properties. Used in foil wrappers, cups, trays, and laminated films. Microwave Compatibility: Studies show aluminum does not significantly interfere with microwave performance. Collapsible Tubes: Used for viscous products and preferred for their ability to prevent air contamination once squeezed. Glass Packaging: Manufacturing: Glass containers are made by melting a mixture of sand, soda ash, and limestone. The glass is shaped using blow-and-blow or press-and-blow processes. Advantages: Impermeable to moisture, gases, and microorganisms, inert, and recyclable. Glass is also transparent, allowing for visual display of contents. Disadvantages: Higher weight leads to higher transport costs. It is more susceptible to breaking and thermal shock compared to other materials. This overview includes the manufacturing and characteristics of various packaging materials, with a focus on their advantages, disadvantages, and specific uses. Would you like to continue summarizing or expanding on any particular part? The text provided offers a comprehensive discussion on various types of packaging films, including flexible films, single films, coated films, and laminated films. It highlights their properties, manufacturing processes, and applications, with a focus on their suitability for food packaging. Here are key points from each section: 1. Flexible Films: These are non-rigid plastic polymers that are less than 0.25 mm thick. Properties: Cost-effective, barrier properties (moisture, gases), heat-sealable, easy to handle and print, and space-efficient for storage and distribution. Common materials include polypropylene (OPP), polyethylene terephthalate (PET), low-density polyethylene (LDPE), and high-density polyethylene (HDPE). Films can be used singly, coated, or produced as multi-layered laminates. 2. Single Films: Types of films include cellulose, polypropylene, PET, LDPE, HDPE, polystyrene, nylon, and various other polymers. Films like OPP and PET offer good tensile strength, moisture barriers, and flexibility, while others like LDPE provide cost-effective, heat-sealable options for shrink-wrapping. 3. Coated Films: Films are coated with other polymers or materials like aluminum to enhance their barrier properties. For example, coatings of nitrocellulose, polyvinylidene chloride (PVdC), or aluminum improve moisture, gas, and odor resistance and heat-sealability. 4. Laminated Films: Lamination of multiple films improves the overall package's properties, such as appearance, barrier strength, and mechanical durability. Common laminates include combinations of nylon, LDPE, PVdC, and EVOH for non-respiring products, and PVC and LDPE for respiring MAP products. The advancements in film technology, such as the use of thinner materials, multi-layer constructions, and special coatings, have led to more efficient and sustainable packaging options in the food industry. It appears you\'re discussing various types of film materials used in food packaging, including coextruded films, edible and biodegradable films, and rigid and semi-rigid plastic containers, along with paper and board packaging. Here's a summary: 1. Coextruded Films: Advantages: These films combine multiple polymer layers to create high barrier properties, are thinner than laminates, and more cost-effective. They are less likely to separate compared to laminates. Materials: Typically made from olefins (PE, PP), styrenes (polystyrene, ABS), or PVC polymers. Methods: Blown films and flat-sheet coextrusions. Blown films are suited for high-speed packaging, while flat-sheet coextrusions are used for rigid forms like pots or trays. 2. Edible and Biodegradable Films: These are made from natural polymers (e.g., corn zein, soy protein, collagen) or biodegradable thermoplastic polyesters. While they offer environmental benefits, their mechanical properties can be inferior to synthetic materials, but blending natural and synthetic polymers can improve performance. Applications: Used for food coatings and packaging, with examples including gluten films and chitosan-cellulose blends. 3. Rigid and Semi-Rigid Plastic Containers: Advantages: These containers (e.g., trays, cups, bottles) are lighter, more cost-effective, and tougher than glass or metal. They are also easier to seal and can be molded into various shapes. Manufacturing Methods: Thermoforming, blow molding, injection molding, and stretch blow molding are the primary techniques. Materials: Common plastics include PVC, PS, PP, HDPE, and PET, which are used for various food products such as dairy, sauces, and snacks. 4. Paper and Board: Advantages: Paper is recyclable, biodegradable, and can be easily combined with other materials. It's commonly used for cartons and boxes. Production: Made from wood chips using processes like kraft or sulfite, paper can be treated to improve opacity, smoothness, and printability. This highlights the diversity and complexity of materials and methods used in food packaging, ensuring that packaging solutions meet both functional and environmental demands. This passage provides a comprehensive overview of paper and packaging materials, detailing their characteristics, manufacturing processes, and applications. Here's a summary of key points: 1. Binders in Paper Manufacturing: Various materials like starches, vegetable gums, and synthetic resins are added to improve the strength (tensile, tear, and burst strength) of paper. Resin or wax emulsions are used as sizing agents to reduce water or ink penetration. 2. Pulp Processing: Pulp undergoes a beating process to split cellulose fibers, increasing their fibrillation, which enhances paper strength. The pulp is then dried using heated cylinders and processed into different paper types, including high-gloss machine-glazed (MG) and machine-finished (MF) papers. 3. Types of Papers: Kraft Paper: Strong paper used for sacks, often bleached or unbleached. It has multiple plies for strength. Sulphite Paper: Lighter and weaker, used for grocery bags and sweet wrappers. It may be glazed for wet strength. Greaseproof Paper: More resistant to oils and fats, often used for wrapping foods like fish, meat, and dairy. Glassine: Similar to greaseproof paper but with a high-gloss finish, providing better resistance to water when dry. 4. Coated Papers: Some papers are coated with wax or other materials to improve moisture resistance and allow for heat sealing. Plastic films are also often applied to improve strength and durability. 5. Paperboard Cartons: Paperboard is made from multiple layers, with a top ply of bleached pulp and a lower-grade material for the inner layers. It is used for food packaging, especially when strength and rigidity are required. 6. Moulded Paper Pulp Containers: Lightweight containers made from paper pulp, offering shock absorption without transferring impact to the product. These are used for egg trays, fruit, meats, and other food products. 7. Active Packaging: Includes technologies like oxygen scavenging, CO2 production, antimicrobial action, and time-temperature indicators, which help extend shelf life and ensure food safety. 8. Printing on Packaging: Various methods (flexographic, photogravure, offset lithography, etc.) are used for printing on films and papers. The printing method is chosen based on factors like print quality, speed, and compatibility with the packaging material. This passage touches on a wide range of packaging materials, from basic paper types to advanced, active packaging systems, all aimed at improving the preservation and presentation of food products. This excerpt covers various aspects of packaging, from its role in food protection to the environmental and economic considerations. Here's a brief summary of the key points: Barcodes and Markings Barcodes (e.g., UPC) are widely used for inventory management, improving stock-taking, reducing pilferage, and facilitating marketing analysis. Laser printing technologies enable the addition of production details without using inks, helping reduce waste and improve efficiency. Future trends in packaging might include information storage through micro-dots for languages, nutrition details, or food condition, enabling easier monitoring of food status. Interaction Between Packaging and Food Packaging materials need to prevent harmful chemical interactions with food, such as the migration of plasticizers or metals. Research continues on optimizing coatings for metal containers to prevent spoilage and preserve food quality. Volatile Organic Compounds (VOCs) may transfer from packaging to food, affecting sensory quality. Environmental Impact of Packaging Packaging waste is a significant issue, especially in developing countries where sophisticated packaging is often unavailable. The cost-effectiveness of packaging is measured by comparing materials like glass, plastic, and metal, taking into account factors such as energy consumption and transport efficiency. Packaging Costs Packaging cost comparisons show a significant variation depending on material type (glass, plastic, metal, etc.) and package size, highlighting economic factors influencing packaging decisions. Environmental considerations call for more sustainable packaging practices, including the use of recyclable materials and reducing unnecessary packaging. Production and Distribution of Packaging Advances in packaging material design have reduced the weight of materials used, leading to lower transport costs and environmental impact. Distribution has also become more efficient with the introduction of bulk handling and lightweight packaging, which reduces fuel consumption and resource usage. Consumer Recycling Recycling efforts are essential for minimizing packaging waste, though there are challenges in processing various materials like plastics, which are often not suitable for food-grade recycling. While glass and metal can be recycled efficiently, plastics have limitations, and their production remains heavily reliant on fossil fuels. This passage underscores the ongoing balance between cost efficiency, environmental impact, and consumer convenience in food packaging. **FILLING AND SEALING** Here are the notes based on the content you provided: Filling and Sealing of Containers Developments in Packaging Systems: Over the last decade, there have been significant advancements in packaging systems driven by: Marketing requirements for more attractive packs. Reductions in pack weight to lower costs and meet environmental concerns (energy/material consumption). New packaging needs for minimally processed foods and modified atmosphere packaging (MAP). The need for tamper-resistant and tamper-evident packs. Accurate Filling: Importance: Ensures compliance with fill-weight legislation and prevents overfilling, which leads to waste ("give-away"). Legislation: Some countries regulate the composition of foods (e.g., meat products like pies and canned mixed vegetables), requiring accurate filling of multiple ingredients. Quality Preservation: Seals are the weakest part of a container and can affect food quality and shelf life during storage. Types of Containers: Rigid and Semi-Rigid Containers: Metal and glass containers are supplied clean, typically wrapped in shrink/stretch film to prevent contamination. Wide-mouthed plastic pots or tubs are stacked and contained in fibreboard cases or shrink film. They are cleaned by moist hot air, except when filled with aseptically sterilized food. Laminated paperboard cartons are sterilized with hydrogen peroxide when used for UHT products. Filling Methods: Filling Machine Selection: Depends on product type and production rate (e.g., gravity, pressure, vacuum fillers for liquids). Volumetric Fillers: Common for liquids, pastes, powders, and particulate foods (e.g., piston fillers). The filling head ensures an airtight seal, and the container is filled to the correct weight/volume. Multi-Head Weighers: Can weigh different products simultaneously (e.g., pre-packed mixed salads, nuts, confectionery). Weight-Based Filling: Using net-weight or gross-weight systems, with microprocessors to control the filling rate and monitor weights. Headspace: A required vacuity or expansion space above food to reduce pressure changes and prevent oxidative deterioration. Sealing Methods: Sealing Types: Glass Containers: Pressure, normal, and vacuum seals for different applications (e.g., carbonated beverages, preserves). Cans: Sealed by double seams using a seaming machine. The seam is the weakest point, and dimensions are checked for quality. Easy-Open Ends: Examples include ring-pull closures for beverages and full-aperture closures for meat, snack foods, and nuts. Aerosol Cans: Pre-sterilized top and valve are fitted, followed by gas dosing and pressure checks. Plastic Containers: Sealed with various closures (push-on, snap-on, or clip-on lids), including tamper-evident membranes. Plastic Bottles: Sealed with tamper-evident, reclosable, or pouring spout closures made from polypropylene, polyethylene, or polystyrene. Sealing Materials: Resilient materials (e.g., composite cork, pulpboard) are used as liners to ensure proper sealing. The pressure during the sealing operation must be evenly distributed to create a uniform seal. Other Considerations: Tightening Torque: The pressure applied during sealing to ensure the cap fits tightly and securely. Thread Engagement: Refers to how well the cap's thread engages with the container's rim, impacting the effectiveness of the seal. Let me know if you'd like to add more details or if you need the complete compilation later! Here are the notes based on the provided information: Packaging Methods and Materials Push-on Covers Used for injection-moulded pots (e.g., yoghurt, cream) and jars. Often sealed with a tamper-evident foil or diaphragm. Cases and Cartons Plain or corrugated cases are designed from flat "blanks" which are cut, creased, and folded to form cases. Board is printed, cut, and then glued or stapled into cartons. European Carton Makers Association (ECMA) classifies folding cartons using an ECMA Code. Multiple packs of bottles/cans are held together by paperboard with interlocking lugs, eliminating the need for staples or glue. Rigid laminated paperboard cartons: thermoplastic film on the inside, and two methods of aseptic filling and sealing are used. Flexible Containers Thermoplastic materials or coatings become fluid when heated and resolidify on cooling. Three types of seals are: 1. Bead Seal: Narrow weld at the end of the pack. 2. Lap Seal: Opposite surfaces are sealed, both need to be thermoplastic. 3. Fin Seal: Same surface sealed, only one side needs to be thermoplastic. Suitable for fragile foods (e.g., biscuits). Types of wrappers: Aluminium foil for unusual shapes, twist-wrapped cellulose for confectionery. Types of Sealers Hot-wire Sealer: Metal wire heated to form a bead seal and simultaneously cut the film. Hot-bar Sealer: Heated jaws press the films together to form the seal. Impulse Sealer: Uses cold jaws and metal ribbon to heat and fuse films. Rotary (Band) Sealer: Used for higher filling speeds, forms and seals with metal belts. High-frequency Sealer: Uses alternating electric fields to induce molecular vibration in the film for sealing. Ultrasonic Sealer: High-frequency vibrations generate localized heat for sealing. Cold Seals: Used for heat-sensitive products like chocolate, ice cream. Form-Fill-Seal (FFS) Equipment Vertical FFS: Film pulled over a forming shoulder and filled intermittently. Suitable for powders and granular products. Horizontal FFS (Pillow Pack): Products pushed into a forming tube of film, fast filling speed, suitable for irregular-shaped foods. Modified FFS for Laminated Cartons: Sterilized webs form into vertical tubes, filled and sealed aseptically. Sachet Packaging Machines Horizontal or vertical machines that form packs from films, then fill and seal. Suitable for powders, granules, liquids, and sauces. High filling speeds: 70--1000 packs/min. Shrink-Wrapping and Stretch-Wrapping Shrink-Wrapping: Uses biaxially oriented polyethylene films that shrink in both directions when heated. Films calculated based on package dimensions and shrink allowance. Stretch-Wrapping: Uses tension to wrap polyethylene or PVC around products. Lower energy use compared to shrink-wrapping. Tamper-Evident Packaging Heat-Shrinkable Sleeves: For bottle necks. Foil or Membrane Seals: For wide-mouthed containers. Breakable Caps: Cannot be replaced after breaking. Child-Resistant Closures: Not typically used for food packaging but found in other sectors. Labelling Labels are crucial for marketing and persuading consumers to buy. Common label types: Glued-on Labels: Adhesive applied during labeling. Thermosensitive Labels: Used in biscuit and bread wrappers. Pressure Sensitive Labels: Self-adhesive, pre-coated with adhesive. Insert Labels: Placed into transparent packs. Heat Transfer Labels: Design transferred via heat. In-Mould Labels: Labeling done during thermoforming of containers. Shrink-Sleeve Decoration: For glass and plastic containers. Checkweighing Used to ensure compliance with weight regulations and reduce product giveaway. Automatically removes under-weight packs from the production line. Can be linked to filling machines to improve accuracy. Metal Detection Critical for detecting metal contaminants during processing. Two types of metal detectors: 1. Ferrous-only: Based on alteration of a magnetic field. 2. Balanced Coil System: Induces electrical fields to detect metal contaminants. Reject systems include air-blast, conveyor stop, or pusher arms. Recent developments include microprocessor control for automatic setup and fault identification.