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24 October 2005

How to freeze vegetables

Do you struggle to find the time to cook healthy meals? Freezing vegetables could save some time. But this may not be as simple as it sounds. Here are a few tips.

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Do you struggle to find the time to cook healthy meals? Freezing vegetables could save some time. But this may not be as simple as it sounds.

Here are some tips from the 'South African Deep Freeze Book' by Alice Theron:

Blanching
One cannot freeze vegetables without blanching them first. Blanching is a process during which the vegetables are briefly exposed to boiling and then cooled down rapidly. The purpose of blanching is to inactive enzymes found in all foods, so that they do not cause deterioration in the vegetables during freezing.

To blanch vegetables, prepare the vegetables as if you are going to cook them, i.e. top and tail green beans and cut into pieces, peel pumpkin or butternut, and cut broccoli into florets.

Put a large pot of water on the stove, using just enough water to cover the vegetables and allow to boil briskly. Place the prepared vegetables in a metal basket (pressure cookers usually have three baskets you can use) or a wire sieve.

When the water is boiling briskly, immerse the vegetables in the boiling water until it starts to boil again and boil for between 1,5 and 6 minutes (see below for time chart). Remove metal basket from boiling water and plunge into a bowl containing water and ice to cool the vegetables rapidly. Leave the vegetables in the ice water for the same time as the boiling period.

Drain thoroughly, transfer vegetables into freezer bags or plastic containers, remove all air from the container (see below), seal, and freeze.

Time chart for blanching vegetables
1,5 min - Cabbage, shredded; Peas, small, young & tender
2 min – Spinach
2,5 min - Beetroot (only use small, tender beetroot)
3 min - Beans, green (sliced), Carrots (sliced thinly), Cauliflower (florets), Parsnips (sliced), Turnips (sliced)
4 min - Asparagus, Broccoli, Brussels sprouts, Carrots (diced), Celery (sliced), Corn or mielie kernels
5 min - Carrots (baby)
6 min - Corn or mielies (small cobs)

Vegetables that need special preparation
Mushrooms - treat with ascorbic acid (vitamin C) (buy pure vitamin C tablets at the chemist, crush one or more tablets and use 1/4 teaspoon of the vitamin C powder per litre of water to prevent discolouration), drain, fry mushrooms in oil or butter for 3 to 4 min, place pan in ice water to chill, pack into containers, remove air, seal and freeze.

Potatoes - Raw potatoes can't be frozen because they will turn black. Boiled potatoes should not be frozen on their own as they turn watery. Always blanch potatoes before freezing. To blanch, boil potatoes with or without their skins in unsalted water for 4 to 5 min. Chill them in ice water for 4 to 5 min, drain well, pack into containers, remove air, seal and freeze.

You can also slice potatoes, fry them lightly and then freeze.

Always remember that frozen potatoes should not be thawed – use them directly from the freezer in casseroles or stews.

Pumpkin - Cook pumpkin until nearly tender, drain, chill and mash. Pack into containers, remove air, seal and freeze. Cooked pumpkin in stews, casseroles and pies freezes very well.

Treat butternut and all types of squash the same way.

Tomatoes - Only use ripe, firm tomatoes (not green, or soggy, overripe tomatoes). Peel tomatoes by plunging them into water that is nearly boiling, and when the skins crack, just pull them off.

Cut peeled tomatoes into pieces, place in a pot (don't add anything!), and bring to the boil, but don't cook them. Put pot into ice water to cool, pack tomatoes into containers, add ½ teaspoon of salt to each container, remove air, seal and freeze.

Use in any dish that requires peeled tomatoes without thawing them.

Removing air
You will have noticed that each one of the freezing instructions above requires that all air be removed from the container before freezing. Like blanching and adding ascorbic acid, air must be removed to prevent the vegetables from discolouring and deteriorating during freezing.

You can expel air from plastic bags by either squeezing the bag so that all the air is removed or by inserting a straw and sucking out all the air. Close plastic containers like Tupperware, then open one corner of the lid, squeeze the container and snap lid shut to exclude as much air as possible.

Nutritive value
So what happens to the nutritive value of these vegetables when they are blanched and frozen? If the exposure to heat and water during blanching is strictly controlled and kept as short as possible, the vegetables will not lose a great amount of nutrients.

Vitamins, like vitamin C, can be damaged by excessive cooking in water at high temperatures. Therefore, blanching should be a very rapid process. This will ensure that vitamins aren't destroyed and minerals don't leach out into the boiling water.

Although it is always better to use fresh vegetables for maximum nutritive value, you will still have a product with a high nutritive content if you freeze vegetables as directed above.

For busy people who work and need to cook meals when they get home at night, frozen foods prepared at home or purchased from the supermarket, can be a great help to ensure that the family still gets plenty of variety in their diet. – (Dr Ingrid van Heerden, DietDoc)

(Reference: Theron, Alice (1970). The South African Deep Freeze Book, Howard Timmins, Cape Town)

 
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