Freezing is one of the simplest, quickest and least time-consuming ways to preserve vegetables and fruits. It is a safe alternative to low-acid food canning, for those of you who are wary of, or do not the time or space for home canning. The botulism-causing bacteria do not grow and produce toxins at 32F° (0°C) and below.
Even after harvest, enzymes, which cause vegetables to grow and mature, continue to break down nutrients, convert sugars to starches, and generally degrade flavor and texture–rot and spoilage, in other words. Freezing slows or stops this enzymatic process.
Vegetables must be properly prepared prior to freezing. The best preparation is to blanch vegetables for a brief period, followed by rapid cooling and quick drying before freezing. Always use the best quality of produce you can. Freezing does not improve quality. Sort by size, color and ripeness. Clean and chop vegetables as you like and also to fit your freezer containers. An exception to this process is herbs, which can be frozen blanched or unblanched. See individual herb listings for details.
Tests have shown that vegetables that were blanched before freezing retain up to 1,300% more vitamin C and other nutrients than vegetables frozen without blanching.
There are three methods of blanching: water, steam and microwave. Microwave blanching is considered neither a time-saver nor energy efficient blanching method. Uneven heating and differing oven wattage may result in over- or under-blanching and is not recommended. If you choose to microwave blanch please consult your owner’s manual.
Blanching time is crucial and varies with the vegetable and size of pieces to be frozen. Over-blanching causes loss of flavor, color, vitamins and minerals. Under-blanching speeds up the activity of enzymes and is worse than no blanching. Inadequate blanching is not a food safety issue. Please see individual listings of vegetables for specific blanching times.
Note that freezing does not kill the microorganisms that may be present on produce. While blanching destroys some microorganisms and there is a gradual decline in the number during freezer storage, sufficient populations are still present that can multiply and cause spoilage when produce thaws.
Water blanching is the more generally accepted method of blanching. It’s quicker (once the water has come to the boil) and allows the vegetables to be totally immersed. Boiling water is more effective at getting rid of yeasts, molds and bacteria, and for removing cabbage worms from cauliflower and broccoli. However, there is a loss of water-soluble vitamins.
Steam blanching does a better job of preserving color, flavor, nutrition and texture. The drawback is that optimum results are obtained if the vegetables are in a single layer, so that all vegetables receive the same amount of steam. This may require several, smaller batches than for the boiling water process. Steaming also takes 1 1/2 times longer than water blanching.
For water blanching, bring 1 gallon of water per 1 pound of vegetables to the boil (2 gallons of water per 1 pound of leafy greens). It’s best to have a wire basket, long-handled colander or mesh bag in which to put the vegetables and to lower into the boiling water. Just tossing in the vegetables creates a risk of over-blanching some of them during their retrieval from the water. Water should return to the boil within a minute, if not, you are using too much vegetable for the amount of water. Start counting blanching time as soon as the water returns to the boil.
To steam blanch, use a pot with a tight lid. Put an inch or two of water in the pot and bring to the boil. If using a steamer basket, do not allow the water to touch the bottom of the basket; it must be above the water. Put the vegetables in the basket in a single layer, if possible. Cover. Start counting steaming time as soon as the lid is on. Check about halfway through to make sure the vegetables are not clumping together and that they are cooking evenly. You can also put the vegetables in a mesh or cheesecloth bag and suspend it over the boiling water. Cover as for basket steaming.
The next essential step is to quickly and thoroughly cool the blanched vegetables to stop the cooking process. The sooner the vegetables are cooled after blanching, the more color, texture and flavor will be retained.
Have a large bowl or sinkful of cold, preferably ice, water at the ready (60°F and below). Plunge the basket or individual pieces into the water and allow to cool for as long as the vegetables were blanched (though twice as long for corn on the cob). You can also insert a colander into the bowl of cold water for individual pieces. Refresh the water after each batch, either by changing or adding more cold water and/or ice cubes.
Tip: You will no doubt observe that both the blanching and cooling waters will be colored. These are nutrients leached from the vegetables. Use this water for watering plants and/or as a base for broths and stocks.
Drying prevents ice build-up on the vegetables once they’re in the freezer. This causes a loss of quality. Spread the cooled vegetables on towels (kitchen and/or paper). A table fan will help speed drying (make sure the fan blades are dust free). You can also gently roll up the vegetables in a kitchen towel and gently press them dry.
There are two basic packing methods: dry pack and tray pack.
Dry pack is simply placing the blanched, cooled and dried vegetables into freezer containers or bags. Meal-size portions are best. Freezer containers are made of plastic or tempered glass. They tend to be more moisture and vapor proof, more durable, and more able to withstand temperatures below freezing than containers not specifically made for freezing. Wide-mouth canning jars seem to hold up better in freezers than regular-mouth jars (personal experience). Plastic cottage cheese and yogurt containers and the like, though not designed for freezing, can be used, though they tend to crack easily and also allow moisture in, so use them for short-tern freezing only. Vacuum seal bags are excellent (provided the seal holds). Freezer storage bags work best if you can press, squeeze or suck the air from them before quickly closing. Aluminum paper can be used to wrap vegetables for freezing if overwrapped in a plastic bag to prevent tearing.
So, tightly pack, within reason. Leave a 1/2″ head space at the top of rigid containers and a 3″ head space for freezer bags. Seal or otherwise close according to manufacturer’s instructions and/or common sense.
Tray pack keeps vegetable pieces from freezing together. Place the blanched, cooled and dried vegetables on shallow trays or pans, preferably on a layer of parchment or wax paper. Try to keep the pieces from touching each other. Put in the freezer on a level surface and freeze until firm. Pack as for dry pack above.
Label the packages with name, amount and freeze date. Try to arrange by date, oldest near the front.
Make sure the freezer is set for 32°F or colder.
All vegetables can be cooked from the frozen state, in a small amount of (salted) water, broth or stock. Corn on the cob should be partially thawed for best results. Cook about half as long as you would fresh vegetables. Follow owner manuals if using pressure cookers or microwaves.
You can also thaw vegetable completely before cooking. This is preferable if adding them to soups, stews or risottos, if their addition in the frozen state would have a deleterious effect on the finished dish.
Please refer to individual vegetable listings for specifics.