Food Preservation: Freezing Basics

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Last Updated on March 27, 2024 by Share My Kitchen

Freezing is the most efficient, convenient, and time-saving method of conserving foods. Most foods available can be frozen, except produce with high-water content, cream-based foods, and cooked starchy foods like noodles and rice. These freezing basics will help you avoid freezer burn, which is when ice crystals form on food and cause it to dry out.

Every fresh produce has enzymes, which are compounds that aid plants in ripening and maturing. Enzyme action is slowed down but not stopped when food is frozen. These enzymes can cause color changes, flavor changes, and loss of nutrients during freezer storage if they are not inactivated. Moreover, freezing stops but does not destroy the microorganisms responsible for spoilage and illness.

Freezing Basics: Inactivation of Enzymes in Fresh Vegetables

Contrary to popular belief, publications or folklore, blanching is necessary for high-quality frozen vegetables. The enzymes are inactivated if vegetables are blanched before they can be frozen. The vegetable is briefly exposed to steam or boiling water during blanching. Then, to prevent the vegetable from cooking, it is quickly cooled in cold water (60°F or lower) for the same duration.

Blanching can also help to kill microorganisms that may be present on the vegetable’s surface. Vegetables, like broccoli and spinach, become more compact when blanched. It is important to follow the recommended times for blanching each vegetable. This is because over-blanching can result in a cooked product and loss of flavor, nutrition, and color. On the other hand, under-blanching increases enzyme activity, which is more harmful than no-blanching.

Blanching using microwave ovens has become popular. However, this method is not recommended since it can produce uneven results due to the different heat patterns in a microwave oven or from one microwave oven to another. Microwave blanching is best done with small amounts of vegetables at a time. Hence, you won’t save time when dealing with large quantities.

Freezing Basics: Avoiding Color Changes in Fruit

Enzymes found in fruits can cause browning and loss of Vitamin C. Most fruits are not blanched. Instead, you may use ascorbic acid (Vitamin C) to control enzymes found in frozen fruits. For home use, there are commercial mixtures of ascorbic available to purchase. Lemon juice or citric acid can also prevent the darkening of fruits but are less effective than ascorbic acid. Packing fruit in sugar or sugar syrup is also an option as this will control browning. However, this is still not as effective as ascorbic acid.

Freezing Basics: Avoiding Off Flavors

Rancid-off flavors are another type of change that can happen in frozen products. This happens when fats, such as in meat, are exposed to air for a prolonged period. But, you can use a storage method that ensures air cannot reach the product to control this. Therefore, to reduce the amount of air contact with the product getting frozen, it is advised to get as much air as possible out of the container or freezer bag.

Freezing Basics: Freezer Storage

Keep frozen vegetables and fruits at 0°F or below to preserve their quality. A freezer thermometer is the only way to ensure your freezer is at the correct temperature. Frozen foods stored at temperatures above 0°F will escalate the rate of deterioration and reduce their shelf life. The ice in the food can thaw and then be refrozen if the freezer temperature fluctuates. When this happens, the smaller ice crystals form larger ones, damaging the cells more. So, it creates a mushier product.

The result of moisture loss or ice crystals evaporating off a product’s surface is freezer burn. This is the grainy, brownish spot where tissues became hard and dry. Food with freezer burn can develop off flavors but will not cause illness. You can package the food in heavyweight, moisture-resistant materials to prevent freezer burn.

Freezing Basics: Containers Used for Freezing

Properly packing food for freezing should ensure that they retain its taste, color, moisture content, and nutritive value. These characteristics should be considered when choosing packaging materials:

  • moisture and vapor resistance
  • durable and leak-proof
  • oil, grease, and water resistance
  • not prone to cracking and becoming brittle at low temperatures
  • can protect foods from absorbing other flavors or odors
  • easy to seal
  • easy to label

You can also use rigid plastic containers with straight sides, glass jars designed for freezing and canning, heavy-duty aluminum foil, moisture or vapor resistant bags, and freezer paper. These are all suitable packaging materials. Containers made for short-term storage, such as bread wrap; cottage cheese, milk, or ice cream cartons; regular aluminum foil; waxed papers do not offer adequate protection against flavor, moisture loss, or freezing burn during long-term storage. There are plastic containers intended for long-term freezer storage that may or may not be suitable for direct microwave use.

Feezing Basics: Packaging Foods

Before packing, cool all syrup and food. Then, you should pack food in sufficient quantities to make a single meal.

Cold foods should be packed tightly in containers. Allow ample headspace, the space between food and closure, as most foods expand upon freezing. The food and the size of your containers will determine how much space is needed. Before sealing food bags, remove as much excess air as possible. Then, each package should be labeled and dated. It’s also useful to indicate the number of servings on every label.

Spread packages among already frozen foods to freeze quickly. Leave a little space between the packages, and only add the unfrozen food that will freeze in 24 hours: approximately 2 to 3 pounds of food to each cubic foot of freezer capacity.

Freezing Basics Pointers
Foods should be frozen at 0°F or lower. You can freeze food quickly by setting the temperature control at -10° Fahrenheit or less 24 hours ahead.
Keep a thermometer in your freezer to ensure proper freezing temperatures are maintained.
After they have been sealed and packaged, freeze them immediately.
Don’t overload your freezer with unfrozen foods. Overloading your freezer can slow the freezing rate, resulting in food losing its quality.
Put the packages in contact with refrigerated surfaces in the coldest part of the freezer.
Leave ample space between packages to allow air to circulate freely. Then, once the food has been frozen, you can keep the boxes together.

Freezing Basics: When the Freezer Stops

Keep the freezer closed. If the freezer stops for longer than 24 hours, you can use dry ice (if possible) or transfer the food to another freezer.

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