The Basics of Freezing Produce
Freezing is an excellent way to preserve fresh vegetables at home. Freezing does not sterilize food; the extreme cold simply retards growth of microorganisms and slows down changes that affect quality or cause spoilage in food.
The quality of frozen vegetables depends on the quality of the fresh products and how they are handled from the time they are picked until they are ready to eat. It is important, also, to start with high-quality vegetables because freezing will not improve the product's quality.
Selecting Freezer Containers
Before preparing vegetables for freezing, assemble the containers you will use. The selection of containers depends on the vegetable being frozen, personal preference and the types that are readily available. Containers should be moisture-vapor resistant, durable, easy to seal and should not become brittle at low temperatures.
Containers suitable for freezing vegetables include plastic freezer containers, flexible freezer bags and their protective cardboard cartons, or glass canning jars. Foods packed in wide-mouth jars are easier to remove than those packed in narrow-mouth jars.
Some household containers are not recommended for freezing. The cardboard cartons that milk, ice cream or cottage cheese come in are not moisture-vapor resistant enough. Regular (not canning) jars break too easily at freezer temperatures.
Preparing the Vegetables
Use vegetables at peak flavor and texture for freezing. Whenever possible, harvest in the cool part of the morning and freeze within a few hours. Wash vegetables thoroughly in cold water, lifting them out of the water as grit settles to the bottom of the washing container. Sort according to size for blanching and packing.
Blanching (scalding vegetables in boiling water or steam for a short period of time) is a must for almost all vegetables to be frozen. Blanching slows or stops the action of enzymes that can cause loss of flavor, color and texture. Blanching cleanses the surface of dirt and organisms, brightens the color and helps retard loss of vitamins. Blanching also wilts or softens vegetables and makes them easier to pack.
Blanching time is crucial and varies with the vegetable and its size. Underblanching stimulates the activity of enzymes and is worse than no blanching. Overblanching causes loss of flavor, color, vitamins and minerals. See the directions for freezing each vegetable for the correct blanching times. Water Blanching – For home freezing, the most satisfactory way to heat all vegetables is in boiling water. Use a blancher with a blanching basket and cover, or fit a wire basket into a large kettle with a lid.
Use one gallon of water per pound of prepared vegetables. Put the vegetables in a blanching basket and lower into vigorously boiling water. Place a lid on the blancher and start counting blanching time as soon as the water returns to a boil. Keep heat high for the time given in the directions for the vegetables you are freezing.
Steam Blanching – Heating in steam is recommended for a few vegetables. For broccoli, pumpkin, sweet potatoes and winter squash, both steaming and boiling are satisfactory methods. Steam blanching takes about 1 1⁄2 times longer than water blanching.
To steam, use a kettle with a tight lid and a basket that holds the food at least three inches above the bottom of the kettle. Put an inch or two of water in the kettle and bring the water to a boil.
Put the vegetables in the basket in a single layer so steam reaches all parts quickly. Cover the kettle and keep heat high. Start counting steaming time as soon as the lid is on. Steam blanch for the time recommended for each vegetable.
Microwave Blanching – Microwave blanching is not recommended. Research has shown that some enzymes may not be inactivated. Flavors could be off and texture and color lost. If you choose to risk low quality vegetables by microwave blanching, work in small quantities, using the directions for your specific microwave oven. Microwave blanching has not been shown to save time or energy.
As soon as blanching is complete, cool vegetables quickly and thoroughly to stop the cooking process. To cool, plunge the basket of vegetables immediately into a large quantity of cold water, 60°F or below. Change water frequently or use cold running water or iced water. If ice is used, have about one pound of ice for each pound of vegetables. Cooling vegetables should take the same amount of time as blanching. Drain vegetables thoroughly after cooling. Extra moisture can cause a loss of quality when vegetables are frozen.
Types of Pack
Two basic packing methods are recommended for frozen vegetables – dry pack and tray pack.
Dry Pack – Place the blanched and drained vegetables into meal-size freezer bags or containers. Pack tightly to cut down on the amount of air in the package. Leave 1⁄2 inch headspace at the top of rigid containers and close securely. For freezer bags, fill to within three inches of the top, twist and fold back top of bag; tie with a twist or rubber band about 1⁄2 to 3⁄4 inch from the food. This will allow space for the food to expand. Provision for headspace is not necessary for foods such as broccoli, asparagus and Brussels sprouts that do not pack tightly in containers.
Tray Pack – Place chilled, well-drained vegetables in a single layer on shallow trays or pans. Place in freezer until firm, then remove and quickly fill bags or containers. Close and freeze immediately. Tray-packed foods do not freeze in a block, but remain loose, so the amount needed can be poured from the container and the package reclosed.
Labeling and Storing
Label packages with the name of the product and the freezing date. Freeze at once at 0° F or lower. Because speed in freezing is important for best quality, put no more unfrozen vegetables into the freezer at one time than will freeze in 24 hours–usually two to three pounds of vegetables per cubic foot of freezer space.
For quickest freezing, place packages against the refrigerated surface of the freezer. After vegetables are frozen, rearrange the packages and store close together. Most vegetables maintain high quality for 8 to 12 months at 0°F or lower. Longer storage will not make food unfit for use, but may impair quality.
It is a good idea to post a list of the frozen vegetables near the freezer and to check off packages as they are used. Remember, frozen vegetables should be cooked without thawing.