How to use the DRYIT semi-continuous tray dryer
Practical Action
water that contains a chlorine based bleach to reduce the contamination by microorganisms.
One method is to prepare a washing solution containing 2 tablespoons of normal chlorine
bleach per gallon of clean water and let the herbs soak for 10 - 15 minutes. There is no need
to rinse because the subsequent stages will ensure that the chlorine is not present in the final
product.
5. Once washed and cleaned the raw material can be peeled or chopped or sliced or diced
depending on the material and what the final form should be. See section on surface area
above.
All the tools should be thoroughly cleaned before use to avoid cross contamination ie there is
no point in virtually sterilising the raw material if dirty knives will then be used to cut up the
raw materials.
6. The raw material can now be weighed to give the amount that will be dried. At this point
the percentage of purchased raw material that cannot be used for processing can be
calculated. A loss of 20%, for example, implies that the value of the raw material has
increased by a factor of 1.20 per kg. Once an established production line has been set up
this step is less important because average raw material loss data will have been built up and
can be used.
7. Some fruits and vegetables are particularly susceptible to turning brown when the flesh has
been sliced\chopped etc and exposed to the air. To minimise this the cut pieces can be
stored in water.
8. The following three stages will very much depend on the type of raw material that is being
processed.
Blanching inactivates components in the foodstuffs called enzymes that may cause loss of
colour in, for example green vegetables, or browning in, for example, apples. Blanching also
has the effect of making the movement of water through the raw material to the surface easier
during the drying process. This results in both faster drying and an improved quality when the
dried food is rehydrated.
Blanching also has the effect of reducing the contamination by micro-organisms. However
this situation can easily change if the raw material is then exposed to unhygienic practises
after blanching. For example dirty tables or other pieces of equipment which may come into
contact with the raw material.
Blanching is generally recommended for roots and tubers and vegetables. Blanching is usually
not carried out for fruits and very rarely for herbs and spices.
Blanching methods
Blanching methods involve dipping the raw material in boiling water for about 3-5 minutes.
However there are a number of factors which affect the time of blanching such as the size of
the pieces to be blanched, the amount of raw material blanched at anyone time and the
temperature of the water.
The easiest way to dip the raw material in the boiling water is to use a cloth bag or sieve.
After blanching, the raw material should be dipped immediately into cold water to prevent
over-blanching or cooking. This cooling step will assist in maintaining good colour of, for
example, green vegetables. However there is a greater loss of nutrients. Cooling in air
(preferably cool and moving) is better for retaining vitamins and nutrients.
Blanching can actually help to ensure that, for example, the green colour in vegetables
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