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THIS EDITION'S FOOD PROCESSING
TECHNOLOGY
Drying
Drying increases shelf life by stopping the
reactions that spoil food - this is a well known and widely used fact.
The subsistence farmers of Africa
have dried the cereals for thousands of years, the fishermen of Africa
dry the fish they catch and the housewives of Africa dry leafy green
vegetables for their family. What they all know is that the product must
be dried properly (the sorghum is not harvested until dry enough) and
kept dry (grain storage systems of all kinds are used). The picture to
the right show a range of dried products on a street market in Morocco.
There is a move towards using drying of
fruit to reduce losses during gluts and to produce products that can be
more conveniently sold than fresh fruit.
Sun Drying
You will often hear people listing the
disadvantages of sun drying and implying that it is outdated and should
not be used. Be aware that sun drying is still practiced widely. As
an example Angas Park Fruit Company in Australia dries and sells some
18 000 ton a year of sun dried fruit.
 Their production system
has been developed to allow them to meet quality system standards
including ISO 9002 and HACCP.
It is not only on the large scale that sun
drying is carried out. In China small scale drying is carried out
widely.
Sun drying is the simplest drying
technology and has the advantage that it requires almost no investment.
The fruit or vegetable is:
-
selected, rinsed, sliced and treated
-
pre-treated if appropriate
-
exposed to direct sunlight
-
turned periodically
-
tested for dryness
-
removed and packaged for storage
What needs to be considered is where you
put the fruit or vegetables to dry. In its simplest form the fruit or
vegetable is place on a rock in the sun. To make things portable you
could use a surface of inert material which can be placed somewhere
appropriate in the sun. Even better is to build a tray
 with a perforated
plastic material (plastic mesh, shade cloth) on a frame - this allows
drying from the bottom as well as the top. If possible the frame should
be made from plastic. The reason for this is that wood, which is
a widely available, is not easy to clean so that you can be sure there
is no old
 fruit or vegetables on it or in the grain or cracks in the
wood. This old food can allow micro organisms (germs) to grow and
survive - these can then get into the fresh fruit or vegetable and grow
there resulting in unsafe and/or spoiled fruit and
vegetables. A simple way of making a plastic frame is to form a
hoop from a 2 meter or so length of 25mm PVC irrigation
pipe.
A few of these trays and more conventional
square ones made from wood, all using shade cloth as the tray media, are
shown in a rural drying course show the range of what will work.
The hygienic disadvantages of some of these solutions can easily be
overcome by not using them continuously but rather allowing them to dry
well. this eliminates the buildup of microorganisms.
This outline of drying is expanded in a
large number of documents and manuals. Many of these are published
on line - three examples of these are given below.
Drying
Fruit and Vegetables from Virginia Tech Extension gives good
detailed information on most apects. To get this document by email use
the web by email link
<<Drying
Fruit and Vegetables>>.
A
document that has information of
sun drying in South Africa's rural
communities with some specialised and focused information is
provided by the National Department of Agriculture. To get this document
by email use the web by email link
<<Sun
Drying in South Africa>>.
For
a really
step by step description
this information developed for the Peace Corps would appear to allow one
to establish drying without any technical background. To get this
document by email use the web by email link
<<Peace
Corps drying manual>>.
When people look at sun drying they often
identify the following problems:
-
needs warm, dry and
windy conditions
-
inconsistent because
of changes in the weather
-
potential
contamination by insects, birds and rodents
-
possibility of
contamination with dust
-
reduction in
nutritional content because of direct to
These points need to be
addressed in any enterprise using or planning to use sun drying.
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