Potatoes - storage and processing
Practical Action
When potatoes are peeled and sliced, browning of cut surfaces takes place due to a natural
enzyme in the potatoes. This can be reduced or prevented by immersing the slices under water
with or without the addition of a small amount (e.g. 2%) of citric acid (lemon or lime juice can
also be used but these flavour the products, which may be unacceptable). Blanching can also
be used to prevent browning of potatoes before they are fried. The slices are heated in steam
or in hot water for a few minutes.
Potato slices are fried in a deep-fat fryer (Fig. 6) at 185-190oC for 3 min for crisps and 4 - 6
min. for French fries.
Fig. 6. Deep fat fryer (photo from Deep Fat Fryer Shop at http://fryershop.co.uk)
There are a large number of blended oils available for different applications, but many
processors use sunflower, peanut or palm oils for frying potato crisps and French fries.
Potentially carcinogenic (cancer causing) acrylamide is produced in foods at
the high temperatures used in frying. It can be reduced by selecting
potatoes that have low levels of sugar or by dipping the cut potatoes in citric
acid solution before frying. Less commonly, lower temperature frying or
vacuum frying can also reduce the formation of acrylamide.
French fries are consumed shortly after frying and are packaged in simple wraps to keep them
clean. Potato crisps require packaging to protect them against breakage; to prevent them
picking up moisture that would lead to softening; and exposure to heat, light and oxygen that
would lead to development of rancid off-flavours. To give a long shelf life, they should be
packed into individual packs made from moistureproof, lightproof and airtight plastic films.
Many small-scale processors attempt to use polythene bags, but these are not sufficiently
airtight and polypropylene is preferred. Packs should be heat-sealed and not tied, and ideally
the packs should be printed to exclude light. They are then contained in corrugated cardboard
boxes or other containers to protect them against breakage and light and stored in a cool
place.
A note on other potato products
Potato pulp may be fermented with malted barley or other grains and then distilled to make a
variety of vodka-like drinks (e.g. Cocoroco (Bolivian brandy) and Irish Poteen). Production of
alcoholic spirits requires a special licence in most countries and is illegal in others. Starches
made from potato flour are also used to make a wide variety of extruded breakfast cereals,
snackfoods, pasta and biscuits. The starch is extracted by soaking potato pulp in water and
separating the starch by sedimentation and/or filtration. However, this is not widely done at a
small-scale. Potato chips may also be frozen, either before or after frying (the latter producing
‘oven ready’ chips) and have a storage life of two years when held frozen at a temperature of
minus 18 - 20oC.
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