Difference Between Drying and Dehydration

Key Difference: Removal of water is the main purpose of both the terms ‘drying’ and ‘dehydration’. But the term drying is generally used in case of removal of water using the influence of non-conventional energy sources like sun and wind. Whereas dehydration means the process of removal of moisture by the application of artificial heat under controlled conditions of temperature, humidity and air flow.

DryingDrying

Drying is a mass transfer process consisting of the removal of water or another solvent by evaporation from a solid, semi-solid or liquid. This process is often used as a final production step before selling or packaging products. To be considered "dried", the final product must be solid, in the form of a continuous sheet (e.g., paper), long pieces (e.g., wood), particles (e.g., cereal grains or corn flakes) or powder (e.g., sand, salt, washing powder, milk powder). A source of heat and an agent to remove the vapor produced by the process are often involved. In bioproducts like food, grains, and pharmaceuticals like vaccines, the solvent to be removed is almost invariably water.

Different types of methods used for drying are as follows:

  1. Air Drying: Air drying is a widely-used and reliable drying process, which can be commonly observed in case of wide use of air-dried natural products in most areas of food production.

For food products, there are two different methods of air drying:

  1. Sun Drying: In many countries with high amounts of sunlight and relatively low levels of humidity, raw materials are traditionally dried directly in the air. The natural raw materials are laid out on an open surface for several days, during which time they are turned over multiple times in the sun. This natural process removes water from the natural raw materials, sharply reducing their water content. The amount of moisture that is still retained after this process varies according to product type and customer request. Sun drying is a simple and cost-effective natural process that is used especially frequently for Mediterranean herbs, spices and dried fruits.
  2. Industrial Air Drying: In contrast to sun drying, industrial air drying with its belt dryers and tray dryers allows for more precise control of the drying procedure. Through this mechanized process, a flow of hot air is used to remove moisture very evenly from the raw materials. With this treatment, the natural raw materials gain a long shelf life without the addition of preservatives.
  3. Freeze Drying: Freeze-drying is a method by which natural raw materials may be preserved in a particularly gentle manner without the use of preservatives. The process protects not only the colour and cellular structure of the product, but also, in contrast to the usual drying techniques, it ensures better retention of content and flavour elements.

2. Drum Drying: For pasty or pulpy products, drum drying (also known as roller drying) is the method of choice. During this process, a thin film of the product is spread on top of a revolving drum that is heated from within. The water in the material evaporates within a few minutes, after which the dried product can be removed from the drum surface. ( Worlee)

Applications of drying

  1. Food: Foods are dried to inhibit microbial development and quality decay. However, the extent of drying depends on product end-use.
  2. Non-food products: Among non-food products, some of those that require considerable drying are wood (as part of timber processing), paper, flax, and washing powder. The first two, owing to their organic origins, may develop mold if insufficiently dried. Another benefit of drying is a reduction in volume and weight.
  3. Sludges and faecal materials from sanitation processes: In the area of sanitation, drying of sewage sludge from sewage treatment plants, faecal sludge or faeces collected in urine-diverting dry toilets (UDDT) is a common method to achieve pathogen kill, as pathogens can only tolerate a certain dryness level. In addition, drying is required as a process step if the excreta-based materials are meant to be incinerated.

DehydrationDehydration

Dehydration means the process of removal of moisture by the application of artificial heat under controlled conditions of temperature, humidity and air flow. Dehydrating food is one of the oldest and easiest methods of food preservation. Dehydration makes the food smaller and lighter, making them ideal for backpacking, hiking, and camping. The additional benefit is no requirement of refrigerator.

According to Encyclopaedia Britannica hot-air dehydration was developed in France in 1795. Modern dehydration techniques have been largely stimulated by the advantage’s dehydration gives in compactness; on the average, dehydrated food has about 1/15 the bulk of the original or reconstituted product. The need to transport large shipments of food over great distances during World War II provided much of the stimulus to perfect dehydration processes.

Dehydration equipment varies in form with different food products and includes tunnel driers, kiln driers, cabinet driers, vacuum driers, and other forms. Compact equipment suitable for home use is also available. A basic aim of design is to shorten the drying time, which helps retain the basic character of the food product.

Applications of drying

 Dairy industry primarily makes use of dehydrated food, producing quantities of whole milk, skim milk, buttermilk, and eggs. Many dairy products are spray dried—that is, atomized into a fine mist that is brought into contact with hot air, causing an almost instant removal of moisture content.

 

 

Drying

Dehydration

Definition

Process of removal of water using the influence of non-conventional energy sources like sun and wind.

Process of removal of moisture by the application of artificial heat under controlled conditions of temperature, humidity and air flow.

Methods

  • Air Drying
  • Freeze Drying
  • Drum Drying
  • Tunnel Driers
  • Kiln Driers
  • Cabinet Driers
  • Vacuum Driers

Primary Application

  • Food
  • Non-food products
  • Sludges and faecal materials from sanitation processes
  • Dairy industry

 

References:ecoursesonline.iasri.res.in,agriinfo.in,answers.yahoo.com,worlee.de,wikipedia.org,
pubs.ext.vt.edu,britannica.com
Image Courtesy:preparednessadvice.com,penbaypilot.com

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