First posted on 07-12-2013
Freezing vegetables is a good option for people who want to preserve their garden produce but are daunted by the idea of canning.
“The color, flavor and texture of the produce are often maintained when it is frozen, and the freezing process is easier and less time-consuming than canning,” said Tammy Roberts, University of Missouri Extension nutrition and health education specialist.
Blanch before freezing
Blanching, which involves boiling or steaming vegetables then immersing them in cold water, is necessary to inactivate enzymes, which are proteins that help with the ripening and maturing process, Roberts said. In unblanched vegetables, this process can continue in the freezer, though at a very slow pace.
Timing is critical. “Overblanching can result in a cooked product with reduced flavor, color and nutrients,” she said. “Underblanching can actually speed up enzyme activity, making the food undesirable for eating.”
Blanching time depends on the vegetable and the size of the pieces to be frozen. Recommended blanching times in boiling water for common vegetables are listed below:
• Green beans: 3 minutes
• Broccoli, chopped or stalks: 3 minutes
• Beets, small: 25-30 minutes; medium: 45-50 minutes
• Brussels sprouts, small: 3 minutes; medium: 4 minutes; large: 5 minutes
• Carrots, tiny, whole: 5 minutes; diced or strips: 2 minutes
• Cauliflower: 3 minutes
• Corn on the cob to freeze on small ears: 7 minutes; medium ears: 9 minutes; large ears: 11 minutes
• Corn on the cob to cut for whole-kernel corn: 4 minutes; cool and cut from ear
• Greens, such as spinach: 2 minutes
• Shelled peas: 1 1/2 minutes
• Snow or sugar snap peas: 2-3 minutes
• Summer squash, such as zucchini, in slices or chunks: 3 minutes; grated: 1-2 minutes
Use a gallon of water per pound of prepared vegetable. Place vegetables in a wire basket and lower into boiling water. Cover and begin counting blanching time as soon as the water returns to a boil.
Once the recommended blanching time has elapsed, immediately plunge the basket of vegetables into cold water. Keep the water cold by changing frequently, using cold running water or ice. Cool vegetables for the same amount of time as they have been blanched. Drain thoroughly. Pack in freezer bags or containers; remove as much air as possible before sealing bags; leave a half-inch of space if using rigid containers. Seal tightly, label and freeze.
Freezing: The quicker, the better
“The goal when freezing vegetables is to have the smallest ice crystals possible because they cause less damage to cell walls,” Roberts said. To achieve this, the food needs to be frozen quickly. Many people set the freezer at minus 10 degrees Fahrenheit a day before they are going to freeze food. Once the food is frozen, the thermostat can be set back to zero degrees.
Don’t overload the freezer with unfrozen food. This will slow the freezing process, which makes for larger ice crystals and more cell damage. Only add the amount of food that will freeze within 24 hours - about 2 to 3 pounds of food per cubic foot of freezer space.
For best results, maintain a temperature of zero degrees in the freezer. Quality deteriorates quickly at higher temperatures. Ten months is the maximum recommended freezer storage time for fresh vegetables.
A number of MU Extension guides on freezing, canning and other food-preservation topics are available at local MU Extension centers or for free download atextension.missouri.edu/preservation.
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