Drying of food
Practical Action
The sides can be made from board or
mud-coated basket work. Larger
models can be made from mud,
brick or cement. The insulation can
be wood shavings, sawdust, coconut
fibre, dried grass or leaves, but
should be at least 5cm thick to keep
the inside temperature high. If
insects are a problem, the air holes
should be covered with mosquito
netting. Drying trays should be made
from basket work or plastic mesh.
Metal should not be used as it can
react with the acids in fruits and
some vegetables and cause off-
flavours in the food. These type of
dryers are used for fish, fruit,
vegetables, root crops and oilseeds.
They have capacities of up to 1
tonne.
Figure 7: Cabinet dryer
Chimney dryer
This is a modified cabinet dryer in which a solar collector of black plastic or burnt husks is
covered by clear plastic on a wooden framework. A black plastic chimney heats up the air above
the exit to the dryer and therefore increases the airflow through the dryer.
Which type of dryer to choose?
The design of either type of dryer (direct or indirect) must be adapted to suit local climatic
conditions, the products to be dried and available construction materials.
Factors to consider when selecting a dryer are described in the box below. A checklist
questionnaire at the end of this brief is a useful tool to help decide whether a solar dryer is a
practical option in your locality.
Factors to consider when selecting a dryer
Local climate – is it wet or dry. How many hours of sunshine are there in a day? In
Afghanistan, the climate is generally dry and there is a lot of sunshine, such that sun and
solar drying are easy to do.
The availability (and cost) of materials to build a dryer. This is linked to the end-use of
your fruit and vegetable. If you can sell the product for a good price, it may be worth
investing in a slightly more expensive dryer. Can you join together with other women who
will use the dryer? You could all contribute to the building costs of the dryer and make a
good dryer that will be well used by your community.
The availability of local craftsmen or workmen to build a dryer. You will need somebody
to follow basic plans and construct the dryer. It is useful if they understand how the dryer
works as they will be able to adapt the plans to your local conditions and advise you on how
to use it.
The amount of fruit and vegetables you want to dry. If you have a large volume of fruit
and vegetables to dry, it is best to build several small dryers that can be used at the same
time, rather than trying to make a big dryer that will accommodate all your product. That
way you have more control over the drying conditions and will get a better quality product.
If any of the dryers are broken, for instance if the plastic cover gets damaged, you will still
have others that you (and your neighbours) can use. You can dry more than one product at
the same time.
The value of the fruit or vegetable you are drying. Is it a high value product that you will
be able to sell for a good price or is it a low value product that you will consume at home.
This will help you to decide how much money you can afford to invest in buying a dryer.
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