FPE 5 - Drying of AB Materials PDF

AGBE 3313 FOOD PROCESS ENGINEERING DRYING ENGR. MARC GOMERSON A. CORPUZ Institute of Agricultural and Biosystems Engineering Bataan Peninsula State University – Abucay Campus  DRYING oldest method of food preservation the water content of the food is reduced to critical level below wh...

AGBE 3313 FOOD PROCESS ENGINEERING DRYING ENGR. MARC GOMERSON A. CORPUZ Institute of Agricultural and Biosystems Engineering Bataan Peninsula State University – Abucay Campus  DRYING oldest method of food preservation the water content of the food is reduced to critical level below which microorganisms cannot grow DRYING vs DEHYDRATION DRYING DEHYDRATION DEFINITION The process of removal of solvent The removal of water from a water- from a solid, semi-solid, or liquid containing compound INITIAL COMPOUND A solid, semi-solid, or liquid A water-containing compounds/objects BY-PRODUCT Water or any solvent Water as an essential byproduct PROCESS Can use mild conditions such as the Need more controlled temperature application of hot air, sun- drying, and humidity conditions with etc. sophisticated equipment  DEHYDRATION Dehydration is the removal of water from the water-containing compound. This compound can be an aqueous solution, solid, etc. At the end of the dehydration process, water forms as an essential byproduct. The end product of the process is always solid. Moreover, unlike the drying process, we use specific processes with controlled temperature and humidity conditions. In contrast, hydration is the addition of water molecules to a compound. DRYING / DEHYDRATION Moisture Migration During Drying Process IMPORTANCE OF DRYING PROCESS Prolonged Storage Life: By far, the vast majority of the fruits and vegetables we eat contain more moisture (i.e., water) than any other single component. An added advantage of increasing the shelf-life of fruits or vegetables through dehydration is that they can be shipped longer distances (possibly to foreign markets). IMPORTANCE OF DRYING PROCESS Weight Reduction: By removing most of the water that was originally present, we are left with only the solids and a small amount of water. This makes a very large difference between the weight of the fresh mangoes and those that have been dried. IMPORTANCE OF DRYING PROCESS Volume Reduction: Removing the water from fleshy produce causes them to shrink in size. Therefore, the produce take less volume to store or transport than their fresh counterparts. IMPORTANCE OF DRYING PROCESS Taste and Texture: When water is removed from them, the sugars that were dissolved in their juice remain in the dried flesh. This means that the dried slices of fruit or the dried berries will contain a high concentration of natural sugars and will have a very pleasant sweet taste with a somewhat stronger flavour than the fresh “wet” fruit. Drying also tends to make the flesh take on a leathery texture which creates a pleasant chewy snack. IMPORTANCE OF DRYING PROCESS Form Changes: When some fruits and berries are dried, the final product has such a significant change in properties from the initial material that their dried form is given an entirely different name. Dried grapes become raisins, and dried plums become prunes. IMPORTANCE OF DRYING PROCESS Convenience and Variety: Fruits and vegetables may also be dried as a manner of increasing their convenience for later use, or to add variety to our diets. IMPORTANCE OF DRYING PROCESS Convenience and Variety: Fruits and vegetables may also be dried as a manner of increasing their convenience for later use, or to add variety to our diets. Factors Influencing Product Quality  The importance of selecting the proper starting materials for drying is often overlooked.  Only the best quality produce available should be used.  Any processing facilities that are drying fruits or vegetables should have a set of standards in place to define the quality of their ideal starting material.  Since this is very subjective, we cannot set out any actual standards here. We can, however, look at some of the basic attributes which need to be considered. Factors Influencing Product Quality Overall appearance: In general, they should be free from blemishes such as bruises and insect damage. They may need to be of a certain size or weight to make handling easier. Colour may assist in determining the desired degree of ripeness. As many fruits and berries ripen, their sweetness increases and their texture changes. Both of these are important factors that can be partially assessed by a preliminary visual inspection. Factors Influencing Product Quality Feel Starting materials being selected may need to have a certain degree of firmness that will indicate their level of ripeness or quality for drying. This will help verify the initial visual inspection. Fruits that are overly ripe, or too soft, may be hard to peel and slice. Their texture may not be suitable for processing. Fruit that is too firm may not have sufficient ripeness to have developed the correct level of sweetness. While they are easy to handle and may dry satisfactorily, the taste of the final dried product may not be as sweet as desired. Factors Influencing Product Quality Aroma: It is often possible to pick the desired starting material by examining how it smells. Many fruits, such as mangoes, have a characteristic aroma that may help in assessing the quality of the starting material. In general, any fruit with an uncharacteristic or suspicious odour should be avoided, since it may be spoiled. Factors Influencing Product Quality Source: Any materials for drying and other processing should be bought from trusted suppliers. The fresh fruits and vegetables entering a processing facility can bring many problems with them. As a processor, you need to know the past history of your raw materials which you will ultimately be selling to your customers. Fruit that has fallen from the tree and been picked off the ground often has surface contamination. The causes of this contamination are often from being in contact with droppings of animals such as sheep, goats, or cattle that have been grazing in the areas around the trees. “Windfall” fruit should be avoided whenever possible. Factors Influencing Product Quality Taste: Since your dried fruits and vegetables will end up as a food product, it is a good idea to taste the starting material. Fruits and berries which are not sufficiently sweet or have an undesirable texture, or “mouth-feel”, should not be used. This is a difficult point to describe or define. However, some basic descriptions outlining examples of desirable flavour attributes can go a long way to assuring a higher quality finished product. Factors Influencing Product Quality Variety: Certain varieties of fruits such as mangoes or apples may have better properties for drying than others. Some mangoes are large and juicy with a high level of sweetness. Others may be smaller with a higher fibre content and lower sweetness level. There is also the need to understand which varieties will give you the best finished product to meet the needs of your customers. You may need to process a number of different varieties to satisfy the different preferences of the consumers. An Overview of the Drying Process The Drying Mechanism Most products dry because moisture (which is really water) is removed from their surfaces. If we have a sliced apple, we can see that the surface tends to be wet - especially if the apple is ripe and juicy. It is important that the air used for drying purposes is not overly humid, or saturated with moisture. When warm dry air is blown across the surface of the wet apple slices, it picks up some of the moisture by the process of evaporation. An Overview of the Drying Process The Drying Mechanism As more and more air blows across its surface, moisture from inside the apple slices comes to the surface to replace the moisture that was lost. We call this process of moisture moving from the centre of the material to the outer surface “diffusion”. Moisture that has diffused to the surface is then evaporated and swept away by the moving air. An Overview of the Drying Process The Drying Mechanism Typical stages of drying (Mercer, 2014) An Overview of the Drying Process The Drying Mechanism Drying stages for an actual food material based on weight (Mercer, 2014) FACTORS IN CONTROL OF DRYING: 1. Properties of the Product: a. Shape of the Material: FACTORS IN CONTROL OF DRYING: 1. Properties of the Product: a. Shape of the Material: Spheres - there is a maximization of the amount of material contained within a minimum surface area. The characteristic dimension of a sphere which controls its rate of drying is its radius, or half its diameter. This is because water must move from the centre of the sphere along its radius to reach the surface where it will be removed. Berries and peas are examples of spherically Doubling the radius doubles shaped products. the distance to the surface of a sphere ∙ FACTORS IN CONTROL OF DRYING: 1. Properties of the Product: a. Shape of the Material: The drying of cylindrically shaped products (e.g., whole carrots) is also controlled by their radius. Here too, moisture must travel from the centre along the radius to reach the surface. The main difference between drying spheres and cylinders is the ratio of their surface area to volume which is higher in the case of the cylinders. ∙ FACTORS IN CONTROL OF DRYING: 1. Properties of the Product: a. Shape of the Material: Slabs or flat plates offer a large surface area to volume ratio which increases the rate of drying when compared to spheres or cylinders. The characteristic dimension that controls drying of flat slabs is one-half their thickness if both their top and bottom surfaces are exposed to the flow of air in the dryer. FACTORS IN CONTROL OF DRYING: 1. Properties of the Product: b. Size or Thickness of the Material: Water removal in a drying process depends on how far the water has to travel from the centre of the material to its surface. For this reason, large pieces of food tend to dry more slowly than smaller pieces of the same food. To facilitate drying, it is often best to use pieces which have a small diameter or are not excessively thick. While this factor is closely related to the shape of the material, it is worth mentioning on its own. FACTORS IN CONTROL OF DRYING: 1. Properties of the Product: c. Composition, Structure, and Porosity: An open structure tends to be more porous than a tighter or more dense closed structure. Moisture is able to find its way through the pores and travel to the surface in products with a more open structure. The composition of the material itself has a significant impact on this. FACTORS IN CONTROL OF DRYING: 1. Properties of the Product: d. Initial Moisture Content: The actual amount of water present in a given material will influence how fast it may be dried to a desired final moisture level. It will take longer to dry tomatoes with a higher moisture content than it will for similar tomatoes with a slightly lower moisture content. FACTORS IN CONTROL OF DRYING: 1. Properties of the Product: e. Surface Characteristics: If we consider that the function of the berry in nature is to protect the seeds and ensure reproduction of the plant. For this reason, the skin traps the moisture in the fleshy part of the berry which surrounds the seeds and prevents them from drying out. When we attempt to dry the berries, we need to recognize this and take appropriate steps such as cutting the berries open to permit the removal of the water. Some fruits or vegetables may have deeply pitted surfaces which allow moisture to escape more easily and speed the drying process. FACTORS IN CONTROL OF DRYING: 1. Properties of the Product: f. Amount of Surface Available for Moisture Loss: This is closely related to the shape of the object. One of the key ways in which the rate of water removal can be increased is to maximize the amount of surface area available for moisture loss. Cutting a product into thin slices increases the surface area while reducing its thickness. Both of these approaches are directionally correct in speeding up the rate of drying. FACTORS IN CONTROL OF DRYING: 1. Properties of the Product: g. Seasonal Variation of Material: Certain attributes of fruits and vegetables can vary from one growing season to the next. One of the most obvious is the size. In a good growing season, the fruit may be plump and juicy, while in a poor season, the fruit would tend to be smaller and less juicy. Such differences from one growing season to the next can have significant effects on the processing and drying of food crops. In some cases, there may be differences from one field to another or between crops harvested several days apart. These factors must be acknowledged as part of the overall drying picture. FACTORS IN CONTROL OF DRYING: 1. Properties of the Product: h. Differences in Varieties of Materials: Different varieties of fruits and vegetables do not always have the same drying characteristics. Some tomato varieties, such as the Roma tomato, have been bred to have a lower moisture content than others. This is to increase their solids content for use in sauces and stews compared to others which may be used as garnishes or in salads where a higher moisture level is more acceptable. FACTORS IN CONTROL OF DRYING: 2. Dryer Properties: a. Type of Dryer: b. Dryer Design Features: c. Air Temperature: d. Time Spent in Dryer: e. Relative Humidity of the Air Going into the Dryer: f. Volumetric Air Flowrate: g. Linear Air Velocity: h. Air Flow Patterns and Uniformity of Air Flow: i. Seasonal and Daily Variations in Weather and Air Conditions: FACTORS IN CONTROL OF DRYING: 2. Dryer Properties: a. Type of Dryer: Forced-air dryers rely on heated air being blown by fans across the product. In large industrial processes, the material may be on a mesh conveyor belt being moved through a series of large drying chambers, each with a different set of drying conditions. By comparison, solar dryers often tend to be more gentle in the manner in which heated air is brought into contact with the product. The wide variety of commercially available dryers demonstrates the impact that the type of dryer can have on the product and how one design may be more appropriate for a given application than another. FACTORS IN CONTROL OF DRYING: 2. Dryer Properties: b. Dryer Design Features: Manufacturers frequently incorporate features into their dryers to enhance such things as the uniformity of air distribution or the recovery of heat from exhaust air leaving the dryer. Such features may (or may not) have an impact on the actual drying of the product itself. Uniform distribution of air is extremely important to the water removal from the product. However, heat recovery from the discharged exhaust air would tend to be prompted by financial considerations with respect to energy costs and would most likely have little effect on the actual drying process. FACTORS IN CONTROL OF DRYING: 2. Dryer Properties: c. Air Temperature: The temperature of the air used in the drying process is one of the major factors influencing the rate of drying. Since water removal involves a change of state from the liquid to vapour form, increasing the energy input to a dryer by raising the temperature of the air will increase the rate of drying. While this tends to be the general case, care should be taken to avoid excessively high temperatures which can damage the product, or create an undesirable situation of “case hardening”, which will be discussed later. Temperatures of 50°C to 55°C are often best for food drying FACTORS IN CONTROL OF DRYING: 2. Dryer Properties: d. Time Spent in Dryer: The length of time during which the product is exposed to heated air within a dryer has a major impact on the overall drying process. Drying time is frequently coupled with air temperature and air velocity to define a drying process. FACTORS IN CONTROL OF DRYING: 2. Dryer Properties: e. Relative Humidity of the Air Going into the Dryer: Relative humidity is an indication of the amount of water vapour contained in a given amount of air divided by the maximum amount of water vapour the air could hold at that temperature. It is expressed as a percentage value. The moisture content of air entering a dryer will have an effect on the water removal capabilities of the air once it is heated. If the relative humidity of the initial air is high before it is heated, then the water content of the air (measured in grams of water per kg of dry air) will be high. This means that when heated, the ability of the air to remove water will not be as great as if the air had a lower initial water content. FACTORS IN CONTROL OF DRYING: 2. Dryer Properties: f. Volumetric Air Flowrate: Volumetric air flowrate is an indication of the volume of air being blown into a dryer in a given period of time. For large dryers, it may be measured in units of cubic metres per minute or per second. Since the volume of most dryers is a constant and the cross-sectional area of the dryer does not change, the volumetric flowrate has a direct impact on the linear velocity of the air in the dryer. Volumetric air flowrates can be set by adjusting the speed of the fan or by other methods such as opening or closing louvres or adjusting volume control disks on certain types of fan assemblies. FACTORS IN CONTROL OF DRYING: 2. Dryer Properties: g. Linear Air Velocity: Linear air velocity really tells us how fast the air is moving in a particular direction through the dryer. As such, it has units of distance divided by time (e.g., metres per second). It is important for the linear velocity of the drying air to be high enough so that it can sweep the moist air away from the surface of the material A hand-held anemometer being dried and replace it with a fresh supply of warm dry air. for measuring air velocities FACTORS IN CONTROL OF DRYING: 2. Dryer Properties: h. Air Flow Patterns and Uniformity of Air Flow: If the airflow is greater in one particular area than another, there will be uneven drying. The area with the increased airflow will tend to become dryer than the areas with the lower airflow. This means that the final product from the dryer will not have a uniform moisture content. There may be areas which are still damp and areas where the product can become overly dry. Non-uniform airflow problems are particularly noticeable in dryers where the air is blowing upwards through a bed of product supported on a wire mesh.  FACTORS IN CONTROL OF DRYING: 2. Dryer Properties: i. Seasonal and Daily Variations in Weather and Air Conditions: In some cases, the daytime air may be very hot and feel quite dry. However, when the sun goes down, the air may feel quite cool and even moist or humid. These changes can have a pronounced effect on the operation of a dryer (see “Relative Humidity of Air Going into the Dryer”), as well as on the product leaving the dryer. When product is removed from a dryer, it is often still warm and has a low moisture content. If it encounters cool, moist air, the product will begin to absorb moisture from the air and its moisture content will increase. This type of variation can also occur between the wet season and dry season in various countries. You need to be aware of any impact that moist air is having on the dried product as well as on the operation of the dryer itself. Effects of Drying on the Finished Product: Nutritional Degradation: One of the primary functions of food is to provide nutrients to the body. Among the components found in food are those which are sensitive to heat. These include vitamins. When subjected to excessively high temperatures the beneficial properties of these components are either completely destroyed or substantially reduced. Loss of Structural Integrity: If too much moisture is removed or the temperature of drying is too high, products may become brittle and literally crumble into small pieces rather than retaining their original desired structure. It may be necessary to have a brief period of high temperature drying at the very start to set the structure of a product, but this should be done very carefully. Effects of Drying on the Finished Product: Reduction in Functionality: Just as vitamins lose their beneficial properties when exposed to excessive temperatures, other functional components present in food products may also experience undesirable changes due to improper drying. In cases where there are starches present, using temperatures over approximately 60⁰C can gelatinize the starch. Products may require the starch to be ungelatinized so that it will thicken later when used in the finished product. If the starch is gelatinized in the dryer, this will not happen. Effects of Drying on the Finished Product: Flavour and Aroma Changes: Flavour and aroma are often due to the presence of essential oils. It is these oils which make oranges smell and taste so pleasant. If attention is not paid to the drying conditions of products containing delicate oils, the oils themselves may be driven off by the heat or oxidized by chemical reactions with oxygen in the heated air. Some processors collect the volatile aromatic compounds leaving their processes by condensing the vapours. Case Hardening: As moisture is removed from fruits or vegetables, their cellular structure begins to collapse and the cells become smaller. The result of this is the shrinking of the product as it dries. Effects of Drying on the Finished Product: Colour Changes: We are all familiar with the colour that develops when we toast bread. While this may be okay with bread, it may not be acceptable if your final product must be white in colour. Browning or toasting can occur by several reaction pathways during the drying process if conditions of temperature and time are excessive. Loss of Nutrients by Water Leaching: In cases where the dried material is rehydrated by placing it in hot or boiling water, the nutrient deposits on the surface can be easily washed away and be lost in the bulk of the water that will ultimately be discarded.  Ways of Expressing Moisture Content: Wet Basis Moisture: One way of expressing how much water is present in a material is to divide the amount of water present in a sample by the total weight of the sample and multiplying this value by 100%. The result is the percent moisture the sample contains. Since the total weight of the sample contains the weight of water and solids in the sample, the value is referred to as the percent moisture on a wet basis. Ways of Expressing Moisture Content: Wet Basis Moisture: If you know the percent moisture present in a sample, you can easily calculate the percentage of solids present, based on the relationship: Ways of Expressing Moisture Content: Table 7-1 (Mercer, 2014) shows some representative examples of wet basis moistures of other foods. Actual moisture contents may vary with varieties, locations in which they are grown, and growing conditions. Ways of Expressing Moisture Content: Dry Basis Moisture: The second method of expressing how much water is present in a material is “dry basis moisture”. Although it is not as commonly used as the “wet basis moisture”, it is much more important in most drying- related calculations. To calculate the dry basis moisture, you need to divide the amount of water present in a sample by the weight of dry material present in that sample. Ways of Expressing Moisture Content: Dry Basis Moisture: The units associated with this calculation will be “grams of water per gram of dry solids” or “kg of water per kg of dry solids”, or some similar set of dimensions with the weight of water per unit weight of dry solids. Since we are dealing with food products which generally contain only water and dry material, we can say: (Mercer, 2014) (Mercer, 2014) Converting from Wet Basis to Dry Basis Moisture: In most drying-related calculations, we need to have the dry basis moisture. However, moisture contents are usually given on a wet basis. Fortunately, the conversion from wet basis moisture value to its corresponding dry basis moisture is not really too difficult. The key to doing the conversion is understanding what is meant by “wet basis” and “dry basis”. “Wet basis” moistures tell us the weight of water as a percentage of the total weight of a sample. In order to calculate a “dry basis” moisture, we need the weight of water contained in a given weight of dry solids. Recognizing how these two are linked together is the key to doing the conversion from wet basis to dry basis moistures. (Mercer, 2014) (Mercer, 2014) Drying Methods Direct and Indirect Heating (Mercer, 2014): Direct heating Here, the drying medium is air which has been heated prior to entering the drying chamber. It may be heated by passing it through the flames of a burner (such as a natural gas burner, etc.), or by passing it across heated metal surfaces where it picks up heat that it then carries and transfers to the material being dried. There may be cases where it is not suitable to dry materials with the direct application of heat from hot air. In these instances, the product may be brought into contact with heated surfaces and the heat can then be transferred to the material in this manner. Hot surfaces such as those on the outside of rotating metal “drums” with steam circulating through them are one method of indirect heating that may be used. Drying Methods Direct and Indirect Heating (Mercer, 2014): Drying Methods Batch and Continuous Dryers (Mercer, 2014): when we dry small quantities of materials in the laboratory (or even in our kitchen). We often put the material inside a bench-top dryer (or our kitchen oven); we start the dryer to remove moisture; and finally, we take the dried material out of the dryer once the desired final moisture has been reached. This process is referred to as “batch drying”. The dryers are called “batch dryers” since we have dried the material in small batches. For larger, commercial scale drying applications, it is not really practical or efficient to use a batch dryer. You cannot keep putting in small amounts of material and removing them after they are dry. This is much too labour-intensive; far too slow; and just not practical. In cases where you may have many kilograms of material to dry and you will be working at it for long periods of time, “continuous dryers” are best suited for the task. Drying Methods Batch and Continuous Dryers (Mercer, 2014): Batch Dryer (Mercer, 2014): Drying Methods Batch and Continuous Dryers (Mercer, 2014): Continuous Dryer (Mercer, 2014): Drying Methods Airflow in Dryers Counter-current air flow in a continuous belt dryer (Mercer, 2014): Drying Methods Airflow in Dryers Co-current air flow in a continuous belt dryer (Mercer, 2014): Drying Methods Airflow in Dryers Combined co-current and counter-current air flow in a continuous belt dryer (Mercer, 2014): Drying Methods Airflow in Dryers Cross-current air flow in a continuous belt dryer (Mercer, 2014): Drying Methods Traditional Dryers Sun drying: Drum Dryers: Continuous Through- Circulation Dryers: Freeze dryers Tunnel Dryers: Flash dryers Cabinet Dryers: Plate dryers Tray Dryers: Rotary dryers Fluidized Bed Dryers: Vacuum dryers Vibrating Bed Dryers: Solar dryers Spray Dryers: Roto-louvre dryers Convective Drying In this method sensible heat of heated air is transferred to the wet products by convection. Heated gaseous medium usually air is used. Contact Drying In this method of drying heat is supplied to wet products by conduction. The commonly used heating medium in conduction drying are steam, organic liquids, metals and other materials with high value of heat transfer coefficient. Freeze Drying The material is frozen on trays and then dried under vacuum. Due to vacuum drying, the material dries directly without passing through the intermediate liquid stage. The principle behind freeze drying is that under certain conditions of low vapour pressure, water can evaporate from ice without the ice melting. Freeze drying is generally used to dry sensitive and high value liquid as well as solid foods such as juices, coffee, strawberries, chicken dice, mushroom slices etc. The dried product is highly hygroscopic and reconstitutes readily. Taste, flavour and reconstitution property of fruit juice concentrates is excellent. Method is costly because of the equipment cost. Freeze drying in combination with air drying is advantageous in reducing cost of drying. For example- vegetables pieces may be air dried to about 50 per cent moisture and then freeze dried down to 2-3 per cent moisture. Freeze Drying This method is based on Heat is supplied by radiation or the sublimation of frozen conduction from heated trays and moisture from the wet the temperature of product is not product in a drying raised to above 0°c chamber.  Radiation Drying Heat energy is supplied through the electromagnetic waves. The wavelength of the electromagnetic radiation lies between 0.76 to 400 micron. The moisture migration inside the materials and diffusion of vapor follow the same laws as in convection or contact drying Super Heated steam drying Superheated steam drying (SSD) uses steam heated beyond its boiling point to remove moisture from materials. This creates a unique drying environment with several advantages over traditional hot air drying. Advantage Faster drying Higher quality Energy efficiency Sanitization  Fluidized Bed drying In this method of drying The materials are products are being dried fluidized by drying air under fluidized condition in with sufficiently high a dryer. velocity to cause suspension.  Deep Bed Dryers A deep bed dryer is a type of industrial dryer that's used to remove moisture from large volumes of material. The most common shapes are round or rectangular. Flat bed dryer The Flat Bed batch type dryer is similar to deep bed dryer except that the surface area of the dryer is more and the depth of the drying layer is less. These dryers are usually of 1-2 tones capacity. Recirculating Dryer In a re-circulating dryer the same quantity of grain is recycled through the dryer until final moisture content is reached. Recirculatory batch dryer is a continuous flow non mixing type of grain dryer. Rotary Dryer The foodstuff is contained in a horizontal inclined cylinder through which it travels, being heated either by air flow through the cylinder, or by conduction of heat from the cylinder walls. In some cases, the cylinder rotates and in others the cylinder is stationary and a paddle or screw rotates within the cylinder conveying the material through. Tray Dryer Also known as cabinet dryer. It is a rectangular chamber made up of steel which is insulated. Trays are placed one above the other and products are spread on the tray uniformly to a height of 0.1-1 cm. It consists of a fan, a heater and thermostatic control to heat air to desired temperature  Tunnel Dryer Tunnel dryers consist of long tunnels through which trucks carrying stacks of trays travel with or against a stream of drying air. The material to be dried is evenly spread on the trays. Spray Dryer Spray drying is a method of producing a dry powder from a liquid or slurry by rapidly drying with a hot gas. Spray Dryer is widely used industrial process for transforming liquid feeds into dried particles  Vacuum Dryer A Vacuum Dryer is used dry the materials by the application of vacuum. Hence, water evaporates faster. The heat transfer becomes efficient for example; the rate of drying enhances substantially Drying Methods Emerging Technologies: Heat pump dryers Cyclic pressure / vacuum dryers Intermittent batch dryers High electric field dryers Vacuum fluid-bed dryers Superheated steam at low pressure dryers Sorption dryers Pulse combustion dryers