5 Drying Drying is one of the oldest preservation methods. The moisture level of agricultural products is decreased to 10-15% so that the microorganisms present cannot thrive and the enzymes become inactive. Further dehydration is usually not desired, because the products then often become brittle. | 5 Drying Drying is one of the oldest preservation methods. The moisture level of agricultural products is decreased to 10-15 so that the microorganisms present cannot thrive and the enzymes become inactive. Further dehydration is usually not desired because the products then often become brittle. To ensure that the products do not spoil after being dried they have to be stored in a moisture-free environment. Drying is generally not difficult. Since the products lose water they also become much lighter and thus easier to transport. Two disadvantages however are that the products also lose vitamins and they change in appearance. This chapter describes how vegetables and fruits are dried. More information on drying beans grains and other products can be found in Agrodok 31 The Storage of Tropical Agricultural Products. The most common drying method is exposure to air. Air can absorb water and the warmer the air is the more it will absorb. For optimal results the air should be hot dry and in motion. In a closed environment the air has to be refreshed regularly because it will otherwise become saturated with the moisture it absorbs from the products. Good ventilation is therefore essential. For drying the relative humidity RH of the air should be less than 65 . If the RH is higher than 65 the fruits and vegetables will eventually dry out but not in the right way. When the sun is shining the RH is usually lower than 65 but when it is cloudy and definitely when it is raining the humidity is usually higher. Sunshine is therefore extremely important For this reason it is not possible to dry products in this way in every season of the year. Before drying the vegetables and fruits have to be thoroughly washed and cut into pieces if necessary. Sometimes extra preparation is needed to retain the product s colour and to minimize nutrient loss. Drying 31 The various preparation methods are described in Chapter 3 and a list of methods required for drying each agricultural product
