Chapter 1 - The Raw Material and the Process PDF

# Chapter 1: The Raw Material and the Process ## 1.1 Introduction Food processing is seasonal in nature, both regarding the demand for its output and the availability of its raw materials. Many of these materials must be imported. Similar to any other manufacturer, the food processor would prefer...

# Chapter 1: The Raw Material and the Process ## 1.1 Introduction Food processing is seasonal in nature, both regarding the demand for its output and the availability of its raw materials. Many of these materials must be imported. Similar to any other manufacturer, the food processor would prefer his raw materials to have the following characteristics: * **Continuously available** in sufficient quantity and quality to enable year-round operation. * **Stable in storage**. * **Uniform characteristics**. * **Predictable price**. In practice, few of these criteria are met. This chapter will explore the specific raw material requirements within the food industry, point out some of the difficulties involved, and discuss how the industry and its suppliers respond to these challenges. The **process suitability (S)** of a food raw material is determined by a balanced assessment of its properties, including: * **Availability (a)** * **Geometric (g)** * **Physical (p)** * **Functional (f)** * **Growth (gr)** * **Mechanical (m)** * **Thermal (t)** * **Electrical characteristics (e)** Therefore: $S = (a + g + p + f + gr + m + t + e + ...)$ (1.1) The relative importance of these factors varies depending on the specific raw material, the process applied, and the final product. ## 1.2 Geometric Properties of the Food Foods with regular geometry are best suited for high-speed, mechanized processes. Here are some examples: * **Potato varieties** with smooth shapes and shallow eyes are preferred for mechanical peeling and washing. * **Smooth-skinned tomato varieties** are easier to wash than ribbed varieties, which tend to harbor insects. * **Pigs with long, lean backs** are better suited for bacon production. * **Straight runner beans** are better suited for mechanical snipping (topping and tailing), as well as slicing. **Shape, uniformity of shape, freedom from surface irregularities, and size** are important processing factors. ### 1.2.1 Shape The dimensional relationships of a food unit are important in the following areas: * **Packaging** * **Controlling fill-in weight** * **Freezing** * **Canning and other heat processes** * **Determining the way in which materials behave during pneumatic conveying and bulk storage** Measuring a set of specimens allows for the estimation of how each dimensional variable contributes to the overall process suitability. For example, Griffiths and Smith found that the volume of quartzite pebbles could be estimated using the following relationship: $log(volume) = b₁.log(major axis) + b₂.log(minor axis)$ This measurement of maximum and minimum dimensions can then be used to estimate the number or weight of an item needed to fulfill a specific container or vessel. ### 1.2.2 Uniformity of Shape Uniformity of shape is important in the following situations: * **Filling into containers** * **Conveying** * **Heat treatment** * **Freezing** * **Dehydration** * **Sorting and grading operations** Some examples include: * **The roundness of biscuits and hamburgers.** * **The sphericity of apples or potatoes.** * **Pears with uniform pyriform shapes.** * **Cucumbers with regular fusiform shapes.** ### 1.2.3 Freedom from Surface Irregularities Surface projections and depressions in a food unit can create problems with cleaning and processing. Since the food industry is labor and energy-intensive, with raw materials accounting for a considerable portion of the cost of processed foods, any surface imperfections removed, either intentionally or during processing, contribute significantly to overall costs. Therefore, it is crucial to select or develop varieties that minimize these defects. ### 1.2.4 Size and Weight of Food Units There are optimal dimensions and weight ranges for each processing method. While sorting can help control these factors, raw materials containing oversize and undersize units can create economic and disposal problems. * **Automatic weighing machines** can measure unit weights. * **Manual weighing** of representative samples can also be used. Uniform size or weight is important for the following processes: * **Heating, cooling, and sterilizing** * **Ensuring uniform fill-in weights in containers** * **Waste control** (e.g. peel-to-fruit ratios) * **Throughput** for individual food unit handling (e.g. peeling or skinning machines) Sampling and testing for size and weight uniformity are critical processes. ## 1.3 Other Physical Properties of the Raw Material In addition to geometric properties, the following physical characteristics are important considerations when selecting food raw materials: * **Color** * **Texture** * **Resistance to mechanical stress** * **Aero- and hydrodynamic properties** * **Frictional characteristics** * **Surface properties** ### 1.3.1 Color Properties * In low-temperature processes (freezing or freeze drying), color changes are minimal, so the initial color is a good indicator of suitability. * In heat processes (canning and dehydration), the initial color is not a reliable indicator of suitability. For example, some apples and pears develop a pink tinge when canned, rhubarb and some cherry varieties become bleached, and chlorophyll in green vegetables is converted to brown-green phaeophytin. * Potatoes present unique challenges; varieties with minimal browning are preferred for canning or dehydration, while a degree of browning is desirable for potato chips. Color control can be achieved through the following: * **Selecting varieties** known for their processing performance. * **Using the correct pretreatment procedures** (e.g. blanching). * **Applying process conditions** that retain the natural color. When necessary, **added colorings** can be used, preferably natural or from the permitted list of artificial colors. Methods for color sorting are discussed in Chapter 3. ### 1.3.2 Textural Properties The textual characteristics of the raw material are important for two reasons: 1. **The material must be sufficiently robust to withstand the mechanical stresses of processing.** 2. **The final product must have the desired texture.** Varieties with improved mechanical strength have been developed, such as tough-skinned peaches and tomatoes suitable for mechanical processing and blackcurrant varieties suitable for mechanical strigging (stalk removal). The evaluation of textural characteristics can be done through: * **Sensory testing** using trained panels. * **Instrumental procedures** using devices like the Tenderometer, Maturometer, General Foods Texturometer, or Instron Food Texture Tester. While there can be variation between perceived and measured texture, instrumental procedures provide valuable insight into predicting the behavior of raw materials during processing. ### 1.3.3 Aero- and Hydrodynamic Properties Differences in aero- and hydrodynamic properties between desired and undesired components of a raw material can be used for cleaning, sorting, and grading (see Chapters 2 and 3). These properties are also essential for conveying, mixing, and processing. The fluid flow characteristics discussed in Appendix I highlight how many of the properties outlined in this chapter (size, shape, uniformity, and surface properties) influence the behavior of particulate foods in a fluid environment. Other relevant properties include density and porosity. Research on these properties has been reported in various publications. Chapter 19 provides a discussion on pneumatic conveying. ### 1.3.4 Frictional Properties Before a granular material can flow down a chute or out of a bin, the forces of static friction (interparticle action and particle-wall friction) must be overcome. Once flow begins, the coefficient of dynamic friction must be exceeded for flow to continue. The frictional properties of food materials are a significant factor in the following areas: * **Gravity and pneumatic conveying** * **Flow into and out of bulk storage vessels** * **Mixing operations**. Differences in friction can be used to separate contaminants during cleaning processes (Chapter 2) and to sort out blemished or damaged units (Chapter 3). Chapter 19 briefly discusses friction theory, and more detailed treatments can be found in other publications. ### 1.3.5 Specific Surface of Food Units This property is significant in processes involving gas/solid and liquid/solid reactions (respiration, extraction, smoking, brining, and oxidation). It is also crucial for economic factors like determining peel and core proportions, as well as washing losses in fruit and vegetable processing. Specific surface properties impact the following: * **Fluidized processing and movement** * **Surface-sensitive phenomena** such as contaminant retention, cleaning, radiant energy transfer (infrared, dielectric, and microwave heating), and aero- and hydrodynamic transfer. Surface area can be measured through: * **Peeling followed by planimeter measurement of the peel area.** Simple relationships between surface area (A) and weight (W) have been established for certain fruits (apples, pears, plums): $ A = K₁ + K₂.W$ Where $K₁$ and $K₂$ are constants. The specific surface of powders can be determined through gas adsorption measurements using nitrogen or helium. ## 1.4 Functional Properties of Food Raw Materials An ideal raw material would: * **Permit maximum process effectiveness,** leading to a first-quality product. * **Possess specific characteristics** that make it suitable for the intended process. Many examples of varieties bred for specific purposes exist, including: * Sheep bred for particular types of wool or meat. * Cattle breeds with specific milk or meat production capabilities. * Wheat varieties yielding flour suitable for biscuits, cakes, or bread. * Potatoes with varying dry solids content. The selection of raw materials often involves **process-testing** to evaluate their functional performance. In some cases, **chemical or physical testing, or a combination of the two**, can be used. An example is the use of specialized equipment, like the **Research Dough Testing Equipment** (Henry Simons Ltd, Stockport, England) and the **Brabender Farinograph** (C.W. Brabender Instruments Inc., N.J., USA), for **evaluating cereal flours used for bread, cake, or biscuit production.** Cultivar testing is typically carried out by trade research associations on a regular basis. ### 1.4.1 Flavor Properties Flavor, often subjective, is a significant characteristic in a mass market, with extremes to be avoided. In some situations, the flavor of the final product is more dependent on additives than the raw materials themselves. * **Strongly flavored syrups** are common in canned fruits. * **Protein hydrolysates and yeast extracts** are added to meat soups. In general, varieties selected for processing should impart only the characteristic flavors of the food, and these flavors should be neither too powerful nor too weak. Flavor is less important than factors like color or texture in determining the suitability of a variety for processing. ### 1.4.2 Resistance to Processing Stress Apple varieties can differ considerably in their suitability for processing. * **Some dessert varieties lose their rigidity during processing and are unsuitable.** * **Firm, white-fleshed, acid varieties are preferred for canning and freezing.** * **Clingstone peaches** have superior texture when canned. * **Marrowfat pea varieties** are used for canned, processed peas, while **tenderer varieties** are better suited for canned or frozen garden peas. Bartlett pears with high acidity and tannin content can develop a pink color when canned. However, the growing conditions and soil types can influence this defect, and a higher pH fruit can eliminate the pink color. These examples illustrate the importance of adequate pilot-testing before approving raw materials for processing. ### 1.4.3 Freedom from Defects Food manufacture is a low-profit activity, and the cost of raw materials is a significant factor. It is crucial to obtain raw materials with minimal defects. Cleaning, sorting, and grading are essential steps in the process, but careful design and operator training are critical for minimizing defect levels. Defects can be introduced during field or orchard production, through the use of varieties with inadequate disease resistance, or during harvesting and handling. These factors significantly contribute to the large amount of waste generated by food processing. The following defects can negatively impact processing suitability: * **Geometric deformities and unequalities.** * **Mechanical damage** (impact, puncture, abrasion). * **Color defects.** * **Insect, animal, fungal, and microbial damage.** * **Extraneous matter contamination.** * **Textural and functional defects.** * **Immaturity or over-maturity.** ## 1.5 Growth Properties of the Raw Material The food manufacturer is increasingly involved in the production of raw materials, extending beyond the factory to the growing area itself. This involvement encompasses contract buying, growth programming, transportation, and storage. ### 1.5.1 Contract Purchasing of Raw Materials In today's market, direct purchases in the open market are largely outmoded. Food processors now contract with farmers and growers ahead of time, securing a specific acreage of produce. This system allows the processor to participate in the following aspects of production: * **Agree on the sowing plan.** * **Supply seed, fertilizer, and sprays.** * **Specify the expected harvest date.** * **Provide technical advice to the farmer.** * **Coordinate harvesting and vining equipment.** * **Provide or arrange transport.** This system works well for a variety of materials, including wheat, barley, rye, potatoes, peas, and beans. It ensures timely and efficient delivery of the required materials in the proper quantities. ### 1.5.2 Selective Breeding of Raw Materials The development of raw materials specifically suited for food processing is a continuous area of innovation. Selective breeding has resulted in improved varieties for various applications: * **Potatoes** with higher dry matter content. * **Tomatoes** producing superior puree in color and flavor. * **Onions** with enhanced dry-matter content. * **Brussels sprouts** with improved freezing properties. * **Cucumbers** with lower bitterness. The widespread adoption of mechanical harvesting has further spurred the development of varieties with suitable growth habits. For example: * **Low, upright, firm-growing pea varieties** with tangle-free pods. * **Fruit varieties** suitable for mechanical plucking or shaking. ### 1.5.3 Maturation Properties The maturity of the raw material is critical in controlling both the quality of the final product and the efficiency of processing. * **Uniform maturity** is necessary for efficient mechanical harvesting. * **Predictable maturity** is essential for proper planning. Over-maturity can result in: * **Increased rejection rates.** * **Excessive product damage.** * **Spoilage during storage.** * **Reduced sterilization efficiency.** Under-maturity can result in: * **Reduced yields.** * **Substandard color, flavor, and texture.** In some foods (meat, cheese, wines), maturity is a desirable goal, while in others (eggs), it is undesirable. Fruits and vegetables can be harvested at various maturities depending on the intended end-use. Peas offer an excellent example of this, with extensive research exploring the impact of maturity on canning and freezing properties. The optimum maturity for a particular purpose can be a very narrow window, making precise timing critical for the processor. ### 1.5.4 Prediction of Maturity Forecasting harvest dates is essential for efficient planning. The Heat Unit System is commonly used for predicting maturity in commodities like peas and beans. The system is based on the principle that maturity is a function of growth temperature. By combining specific growth data for a particular variety with the average meteorological records of the growing area, it is possible to make long-range harvest forecasts. Corrections can be made to these forecasts based on actual weather conditions during the growing period. For example, peas are generally not considered to grow below 40°F (4.5°C). ### 1.5.5 Extension of Harvest Season Using varieties with early, middle, and late maturity allows for a longer harvest season for many crops. * **The broiler and battery systems** have expanded the availability of chicken meat and eggs. * **Broiler systems** are now being applied to beef production with promising results. * **Pea varieties** have been developed with expanded harvest seasons. The availability of raw materials can be extended through various preservation methods: * **Brining** * **Drying** * **Pulping** * **Storage of part-processed or raw materials** These methods often involve additional costs, making it important to carefully consider their economic feasibility. Fish pose unique challenges. Rising harvest costs and the depletion of fish stocks create a challenging situation. **Fish farming** offers potential solutions and is becoming a more viable option, especially for those who rely on saltwater fish. **Hydroponics**, soilless culture, offers another interesting option for extending the harvest season. This system utilizes solar-actuated climate control, simplified disease control, water economies, and concentrated planting. It is becoming a widely adopted commercial practice in numerous countries. ## 1.6 Mechanisation and the Raw Material The soaring cost of labor and the need to improve profitability have led to the increased mechanization of food processing operations. Mechanization, when properly implemented, offers several advantages: * **Increased efficiency.** * **Reduced labor costs.** However, poorly engineered mechanization can result in: * **Excessive product damage.** ### 1.6.1 Product Damage Common causes of damage during food preparation include: * **Operator carelessness.** * **Unsuitable mechanical handling procedures.** * **Poor equipment design.** * **Improper containerization.** Damage can occur at any stage of the process, starting with the grower or breeder and continuing through processing, packaging, and distribution. Damage can manifest itself in various ways that impact the quality and safety of the food: * **Aesthetics:** Bruised or punctured areas. * **Contamination:** Rot infection, infestation by insects or vermin. * **Spoilage:** Accelerated enzymatic and chemical reactions. It is essential to minimize these issues through: * **Careful handling.** * **Properly designed equipment.** * **Appropriate containers.** Damage occurs due to: * **Impact with other produce or hard surfaces.** * **Excessive pressure from overlying food.** * **Puncturing by sharp projections.** * **Abrasion caused by movement and vibration.** Further information on the mechanics of damage can be found in relevant literature. ### 1.6.2 Mechanical Harvesting The transition from selective to mechanical harvesting has significantly reduced labor costs but has also introduced challenges: * **Excessively damaged product.** * **Reduced quality.** * **Increased capital investment and maintenance costs.** Mechanical harvesting requires careful coordination between the field and the factory, often involving modifications to processes and handling systems. The combine harvester, pea viner, bean harvester, and various harvesters for root crops are common in the UK. In the USA, there has been significant progress in the development of harvesters for a wide range of fruits and vegetables, including berries, asparagus, sprouts, cucumbers, cabbage, spinach, and tomatoes. Tree shakers and blowers are used for harvesting apples and citrus fruits. Mechanical harvesting utilizes a variety of principles: * **Shaking of trees or bushes.** * **Combing of berry fruits.** * **Cutting of cabbages, lettuces, and cauliflowers at ground level.** * **Pulling of carrots, radishes, and celery by gripping stems.** * **Stripping of cucumbers and maize ears using rollers.** * **Vining of peas and beans through stripping, pulling, or cutting.** * **Mechanical digging of root crops.** Mechanical harvesting frequently involves additional preparative operations like aspiration, screening, destoning, and color sorting. Implementing a successful mechanical harvesting system requires the collaboration of breeders, farmers, food technologists, engineers, and economists. ### 1.6.3 Design of Transit Containers for Raw Materials In-transit damage due to impact, abrasion, and pressure can significantly impact the quality of raw materials. Studies on tomato handling have shown conflicting results regarding the effectiveness of different container types. For example, some studies have found that shallow lug-boxes help reduce damage compared to bulk bins, while others have found the opposite. These findings suggest that several factors contribute to transit damage: * **The type and variety of fruit.** * **Fruit maturity.** * **Fruit shape and size.** * **The nature of the container surface.** The work of O'Brien and Guillou on a vibration simulator for fruit handling provides valuable insights into these factors. Hammerle's research on abrasion resistance in fruits and vegetables is another important contribution. Pressure damage can occur in deep containers due to the weight of overlying material or in open-top containers when overfilled. ### 1.6.4 Transportation of Raw Materials Ensuring that raw materials of the proper quality are available in the required amounts and at the right time is crucial for any food processing operation. This involves careful planning and coordination. ### 1.6.5 Raw Material Storage Ideally, all raw materials would be processed immediately upon arrival at the factory. However, this seldom occurs in practice, requiring a dedicated storage system. Storage systems should be designed to accommodate delivery delays, plant breakdowns, and bumper harvests. Under specific market conditions, a storage system can be an asset for forward-buying. Storage conditions are critical and require careful consideration of the following factors: * **Temperature.** * **Humidity.** * **The surrounding atmosphere.** Storage can require significant capital investment and operating costs. The demanding conditions imposed by many foodstuffs necessitate careful planning with regard to storage facilities. ### 1.6.6 Emergency Storage In many cases, emergency situations can arise, necessitating additional storage capacity. These situations can be addressed through overtime working or by temporarily renting storage space. Provision of emergency storage capacity should be minimized. ## References 1. Griffiths, J. C., & Smith, C. M. (1964). Relationships between volume and axes of some quartzite pebbles. *American Journal of Science,* *262*(4), 497-512. 2. Mohsenin, N. N. (1980). *Physical Properties of Plant and Animal Materials* (Vol. 1). Gordon & Breach Science Publishers. 3. Arthey, V. D. (1975). *Quality of Horticultural Products*. 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Mariculture and aquaculture. *Food Technology*, *27*(12), 60-66. 14. Anon. (1984). Fish farming. *British Food Journal*, *86*(9/9), 50–52. 15. Rahman, A. R. (n.d.). Hydroponic culture - Past, present, future. Paper presented at Session 01, 1st International Congress on Engineering and Food, Boston. 16. O'Brien, M. (1983). *Principles and Practices for Harvesting and Handling Fruits and Nuts*. AVI. 17. Ryall, A. L., & Pentzer, W. T. (1974). *Handling, Transportation and Storage of Fruits and Vegetables*. AVI. 18. Zahara, M. B., & Johnson, S. S. (1981). Cost comparison of hand and mechanical harvesting of mature green tomatoes. *California Agriculture*, *35*(7/8), 7–9. 19. O'Brien, M., & Guillou, H. (1969). An in-transit vibration simulator for fruit handling studies. *Transactions of the American Society of Agricultural Engineers*, *12*(1), 94-97. 20. Hammerle, J. R. (1970). A technique for evaluating fruit and vegetable abrasion resistance. *Transactions of the American Society of Agricultural Engineers*, *13*(5), 672-675.