Freezing fruits and vegetables involves freezing the water contained in the cells. When the water
freezes, it forms ice crystals, which can puncture the cell walls and cause vegetables to lose some
water. The texture of the thawed produce will therefore be much softer than when it is raw.
It is often therefore recommended that raw frozen fruits are eaten before they have completely
In any case, the vegetable should frozen quickly. When produce is frozen quickly, it forms a large
number of small ice crystals, rather than fewer larger ones. These ice crystals produce less cell wall
rupture so texture is better preserved after defrosting.
Freezing only slows down the enzyme responsible for rotting vegetables, which may eventually lead to
loss of nutrients and colour even while frozen. Vegetables should be rapidly blanched in boiling water
to kill these spoiling enzymes if it is to be frozen.
The other way to preserve vegetables is by canning them, where heat treatment is used to destroy the
spoiling enzymes. The treatment is much more effective.
Vegetables and fruits can also be preserved by drying them, to reduce the cells water content to such
an extent that bacteria can no longer grow.
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Unlike canned vegetables, dried vegetables are indigestible, and need to be cooked to re-introduce
the water that had been lost (i.e. rehydrate them).
The water in which dried vegetables are cooked should never be salted – salt prevents so much water
from entering the dried vegetables by osmosis.
Cooking should be slow to ensure even cooking (rapid cooking at the beginning cooks the external
part to excess, making the outside too soft before the centre is even cooked).
Unlike for fresh vegetables, where cooking in alkaline conditions make the vegetables too soft, adding
bicarbonate of soda to the cooking water improves the softening of lentils by accelerating the pectin
breakdown. Equally acids like vinegar, lemon juice or tomatoes should not be added until the end of