Applications of Effective Food Dryers in the F&B Industry

The role of any Food Dryer is to preserve food by drying, dehydrating, or desiccating it. Drying prevents the growth of yeast, bacteria, and mold by removing water through evaporation. Drying makes use of mass and heat transfer principles. First, the heat is transferred to the product so that the liquid gets evaporated. The mass is then transferred in the form of vapour into the surrounding gas. Drying operations are conducted with constant and falling rates, depending on the critical moisture constant of the product.

Food Drying Principles

Food dryers in the food industry follow the mechanisms:

Hot Air Drying

Here, hot air is the heating medium of choice, and it is in direct or indirect contact with the product. Evaporation of the moisture in the product takes place due to the heat transferred from the hot air.

Surface Drying

Surface drawing is achieved by heat conduction via a heat transfer system. These are also called contact dryers. Here, the wet food is not in contact with the heating medium. They both are separated by a heat transfer surface instead. The heat transfer occurs by conduction through the surface and uses convection to transfer the heat from the hot surface to the product to remove water. This type of Food Dryer uses less air volume than a hot air dryer and provides higher thermal efficiency. Additionally, the process can also be carried out without the presence of oxygen.

Types of Drying Equipment

Spray Dryers

In spray drying, the product that requires drying is suspended in air, and the moisture in it is converted into an atomized foggy mist. This approach provides a large surface area for frying, and the atomized liquid is then made to interact with hot air inside a drying chamber.

Drum or Roller Dryers

The working principle of a roller dryer involves applying a thin film of material to the smoothened surface of a steam-heated metal drum that is continuously rotating. The film is then scraped off at regular intervals using a stationary knife placed opposite to where the liquid material is applied.

Vacuum Shelf and Vacuum Band Dryers

This dryer spreads or sprays the food slurry on to a steel band that passes two hollow drums inside the vacuum chamber. The food first gets dried by the steam heated drum and then by the radiant heaters present over the band.

Tray Dryers

These dryers spread the food out in thin layers on trays where they are dried. Most of them are heated by an air current that sweeps over the tra, which can help in removing liquid vapours.

Tunnel Dryers

Tunnel dryers involve more advanced versions of tray dryers. Trays are placed on trolleys which then move through heated tunnels. In most cases, the air is used in the process.

Fluidized Bed Dryers

In a fluidized bed dryer, the food product is suspended against the direction of gravity in an airstream that flows upwards. Convention makes the air transfer its heat onto the food material.

Pneumatic Food Dryers

The principle behind a pneumatic dryer involves conveying solid food particles in an airstream where the turbulence and velocity of the stream maintain particles in suspension.

Rotary Dryers

The food material is placed and made to travel in a cylinder that is horizontally inclined. The heating is done by airflow or by heat conduction through the cylinder walls.

Trough Dryers

A trough-shaped conveyor belt carries the material to be dried. This belt is made of mesh, and the air blows through the material’s bed. The conveyor belt moves to turn over the food product, thereby exposing the fresh surface to air.

Bin Dryers

Here, the bin contains the foodstuff. It has a perforated bottom which acts as the channel for warm air to blow vertically upwards. This air passes through the food product to dry it.