Do not over-dry fruits and vegetables

TWO Sundays ago, NAREI in Focus began a series on solar drying. The aim is to inform readers of
this green option in food preservation. Sun drying is the simplest and cheapest method of drying. It is used for high volume foods such as grain, rice, sultanas, tomatoes and raisins.

`It is advisable to dry fruits and vegetables in the shade when possible. Excessively high temperatures during drying can lead to high levels of shrinkage in the food. This may make them irregular in shape and unattractive to the consumer. High temperatures also increase the tendency to turn brown. Dried vegetables that are shrunken are more difficult to rehydrate.
The temperature and rate of drying should be strictly controlled. Rehydration of the product is an important quality aspect. Fruits and vegetables that are overdried appear unattractive and are difficult to rehydrate. Over-drying is also wasteful in terms of lost manpower and energy. There is a fine balance between drying to a moisture content low enough to preserve the fruit and high enough to make an attractive product.

SELECTION OF DRYER
Some fruits are dried directly in the sun. Sun drying of fruit and vegetables on the ground should be avoided as it is very difficult to control the quality of the product. When sun drying is used, the fruit and vegetables should be dried on mesh trays on racks that are raised above the ground so that the air can circulate around them. This speeds up the drying process. The fruit or vegetables are loaded onto trays in a single layer. The maximum capacity should be 6kg vegetables per square metre of tray. They should be turned or moved every hour during the first drying period to speed up drying and improve the quality. The trays of produce should be dried in the shade to prevent loss of colour and nutrients.

Shade drying is more dependent on-air movement over or through the fruit or vegetables. The drying rack should be placed in a position that can take advantage of any wind. In dry air conditions with ample circulation, shade drying can be accomplished almost as quickly as sun drying. In conditions of high sunshine and low humidity, sun drying can be finished in one day. If the produce has to be dried overnight, it has to be protected from evening rains and early morning dew.

Solar drying in a cabinet dryer can be used for most vegetables and fruits. During the initial stages of drying it is essential to ensure that there is no condensation of water inside the dryer. Condensation is caused by insufficient air flow. The operator should ensure that the air intake and outlet vents are wide open to prevent this from happening. Solar drying is dependent on the sun shining. There is no drying in cloudy or rainy conditions or overnight. This prolongs the drying period and can reduce the quality of the products. For a small business, solar drying is really only a viable option in dry sunny climates.

Artificial drying is the most controllable method of drying. It is also the most expensive as it requires a drying cabinet that is heated by electricity, gas or biomass. There are several types and sizes of dryer available to suit processors needs. The advantages are that the drying rate can be carefully controlled regardless of external climatic conditions to make a high quality dried product.

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