Dehydration Process
The preservation of fruits and vegetables through drying dates back many centuries and is based on sun and solar drying techniques.
A large number of foods and biomaterials are dehydrated in a variety of units with diverse processing conditions. The choice of drying method depends on various factors, such as the type of product, the availability of a dryer, the cost of dehydration, and the final quality of the desiccated product.
Agriculture has also been developed into an important component of the country’s foreign exchange earnings by exporting different types of fruits, vegetables, and floriculturists.
The market demand and the export demand show 10-12% growth every year. Dehydration is an energy-intensive process, yet fruits and vegetables can be converted into value-added products by using solar energy options and exploiting the remote area labor force. Dehydrated products have potential markets nationally and internationally.
Sorting & Grading:
There is an immense range of agricultural production that can be dehydrated and marketed locally or internationally.
a. Sorting and grading can add 40–60% more value to the produce.
b. Sorting and grading can reduce postharvest losses by:
c. Preventing disease contamination of sound produce, which otherwise occurs when sound and diseased produce are mixed.
d. Minimizing ethylene damage (e.g., premature senescence or ripening), which otherwise occurs when injured produce or ripe fruit (high ethylene producers) is mixed with undamaged produce or unripe fruit.
Cleaning:
a. Clean vegetables have higher market appeal and prices than dirty vegetables.
b. Cleaning reduces microbial contamination, physical damage, and transport costs.
c. Wiping a tomato, eggplant, or cucumber with a clean, soft cloth.
f. Washing using clean water to remove adhering soil and other debris. After washing, the produce should be air-dried before packing.
While cleaning, sorting can also be done. Avoid contact between produce and the soil, which is a rich source of spoilage and human pathogens.
Process of Dehydration:
Microorganisms need water to grow and reproduce.
a) Dehydration reduces the water activity level, weight, and bulk of the food and helps to preserve the product.
b) There are six main dehydration techniques, each of which is suitable for a different range of foods. The main principle behind each method is the same: the removal of humidity to prevent microbial activity.
c) Many products, such as vegetables, crumble before drying to increase their surface area and make water loss much more rapid.
Drying (dehydrating) food is one of the earliest and easiest methods of food preservation. Dehydration is the process of evacuating water or moisture from a food product. Removing moisture from foods makes them smaller and lighter.
Drying Methods:
Sun drying:
This method is one of the most regular methods of drying." The high sugar and acid content of fruits makes them safe to dry in the sun.
It is slow and only practical in hot, dry climates. However, it is still used today, e.g., for sun-dried chilies, raisins, or tomatoes.
Food, such as fish, is also vulnerable to contamination through pollution and vermin, e.g., rodents and flies.
Spray drying:
Spray drying is a method of producing a dry powder from a liquid or slurry by rapidly drying it with a hot gas. This method is suitable for producing products such as dried milk and coffee powder. A fine spray of liquid is injected into a blast of hot air in a chamber. Water evaporates within seconds, leaving the solid part of the product behind in powdered form.
Usually, this powder is too fine to disperse in water, so a little moisture is added to make it 'clump' together into larger particles. This improves the wetability of the product and helps it dissolve more fully when added to water. Fluidized bed drying is used to granulate these powders.
Fluidized bed drying:
Warm air is blown upwards directly underneath the food, causing it to flow and remain separated. This method has been extensively used for drying various products.
Its main advantages are:
Including a high drying rate and excellent gas-solid contact.
High thermal efficiency.
Relatively low cost of operation
This procedure is suitable for small items such as peas and coffee.
Tunnel drying:
Hot air is blown over the products, such as vegetables. Air movement in the drying tunnel of the inlet and outlet vents is important.
Drying time can be shortened by two main procedures: one is to raise the product temperature so that the moisture can be readily vaporized. The second is to treat the product to be dried so that the moisture barriers, such as dense hydrophobic skin layers or long water migration paths, will be minimized.
The main disadvantage of this process is that the product tends to shrink and is less easy to rehydrate.
Roller drying:
The rotary drier is essentially a cylinder, disposed marginally to the horizontal, which may be rotated, or the shell may be stationary, and an agitator inside may revolve slowly. In these, the food is spread over the surface of a heated drum. The food product, in liquid or paste form, is uniformly spread over heated rollers or drums, which rotate slowly. The heat causes the moisture to evaporate, leaving a dried product behind. A scraper then removes this for use. This method is suitable for instant mashed potatoes and baby food and can be applied to, for example, milk, starch, and potato flakes. Drum drying may be regarded as conduction drying.
Accelerated freeze drying:
This method produces an excellent-quality dried product but is both expensive and time-consuming. In most cases, the food is frozen before being loaded into the dryer. Heat is transferred to the food by conduction or radiation, and the vapor is removed by a vacuum pump and then condensed, so it is used for luxury items such as coffee and certain fruits.
First, the produce is frozen. Then the temperature is increased under a strong vacuum. This makes the frozen water sublime, i.e., change directly from ice into water vapor without becoming a liquid. This process involves little or no heating, so there is little shrinkage or flavor change, and the product rehydrates well. The product, however, is very fragile and crumbles easily.
Advantages:
1. Modern production technology has greatly increased the yields of fruits.
2. But unfortunately, one-fourth of the highly perishable produce after harvest is never consumed due to spoilage during its storage, transportation, and processing.
3. The preservation of fruits by drying and dehydration is highly effective and practicable.
4. Dehydrated fruits have been an important food supply in different parts of the world.
Storing Dried Fruits & Vegetables:
Cool-dried food should be placed in a closed container that has been washed and dried before storing. Home canning jars are good containers for storing dried foods. Store in a cool, dry, and dark place. Dried foods can maintain quality for up to a year, depending on the storage temperature. The cooler the storage temperature, the longer dehydrated foods will last.
IMPORTANCE AND BENEFITS OF DEHYDRATED
Reservation and Storage:
Drying is one of the oldest methods of preserving food. It removes enough moisture to prevent decay and spoilage. Using a dehydrator is a great way to enjoy eating produce when it’s technically out of season and is a great alternative to canning or freezing foods.
Convenience:
Dried fruit or vegetables are convenient to pack for anyone “on-the-go” because they don’t need to be refrigerated, they're not messy or sticky, they're compact and don’t take up much space, they don’t weigh much, and they provide quick energy.
When Backpacking or camping, Brighten your meal by adding dehydrated vegetables
Quick Energy:
Speaking of quick energy, dried fruit is very calorically dense. Because the fruit loses water during the drying process, its nutrient, calorie, and sugar content becomes more concentrated. Some would say this is a negative, but I think that depends on who you ask. If you’re out hiking, biking, skiing, or even sightseeing, a high-calorie dried fruit snack is a great way to refuel.
Nutritional Value
Nutritiously, the heat from dehydrating does tend to destroy some vitamins in the food, but fortunately, dried fruit retains all of its fiber and iron. Fiber is associated with lowering the risk of certain cancers, such as colorectal cancer and other gastrointestinal cancers. Also, a home dehydrator is not nearly as harsh on nutrients compared to the commercial process of drying. Dried fruit contains no fat, cholesterol, or sodium. Another perk of using your own dehydrator is that you can ensure no additives or preservatives and also use organic when desired.
Variety with Vegetables
When dehydrating vegetables, select veggies at peak flavor and eating quality. This usually is just as they reach maturity. Sweet corn and green peas, however, should be slightly immature so they retain their sweet flavor before their sugars change to starch. The options are endless when it comes to dehydrating vegetables.
From tomatoes, green beans and kale to bell peppers, peas, and broccoli, the variety is one of the best things about dehydrating.
Advantages of Dehydrating Food
· The main advantages of dry food are that it is convenient for the owner; it's easy to measure, easy to serve, and easy to store.
· They have unlimited shelf life under proper storage conditions.
· Transportation, handling, and storage costs are reduced.
· Provide important modern marketing requirements.
· Easy and economical way to save surplus food for a later time.
· Portability can take it anywhere you go.
· Helps in minimizing post-harvest losses.
· It’s the most nutritious way to preserve food – enzymes, vitamins, and minerals aren’t destroyed by high canning temperatures.
· Dehydrating food is a quick and easy way to preserve food.
· Dried food doesn’t take up much room and is very light.
· Glass, plastic, or metal air-tight food containers can be used to store your dehydrated fruit, vegetables, and meat.
· The storage container needs to be safe from moisture and insects but doesn’t need to be sealed.
· Dried food doesn’t need to be refrigerated.
