Blanch Vegetables Before Freezing
Karma Metzgar, C.F.C.S. Former Northwest Regional Nutrition Specialist, Nodaway County Extension Center, University of Missouri Extension
Every fresh sweet corn season I hear people telling others to preserve their corn by just putting it in the freezer. Unless you are freezing onions or green peppers, blanching is a must before freezing vegetables.
What is blanching and why is it a must?
Blanching is the scalding of vegetables in boiling water or steam. Blanching slows or stops the action of enzymes. Up until harvest time, enzymes cause vegetables to grow and mature. If vegetables are not blanched, or blanching is not long enough, the enzymes continue to be active during frozen storage causing off-colors, off-flavors and toughening.
If you spend the time growing the vegetables, pulling weeds, picking and preparing for the freezer, the blanching time may be regarded as a pain - but it’s necessary if you want fresh garden flavor later.
Blanching time is crucial and varies with the vegetable and size of the pieces to be frozen. Under-blanching speeds up the activity of enzymes and is worse than no blanching. Over-blanching causes loss of flavor, color, vitamins and minerals.
The most convenient way to blanch vegetables is in a large kettle of boiling water. Allow one gallon of water per pound of vegetables. Bring the water to boil and lower vegetables into the water, allowing the water to continue boiling. Cover and start counting the blanching time. I like to use the side burner on my outdoor gas grill for this task. It keeps the heat and steam outside and my kitchen cool.
As soon as blanching is complete, cool the vegetables quickly and thoroughly to stop the cooking process. To cool, drain the vegetables in a strainer, then plunge the vegetables into a container of ice water. Cool vegetables for the same amount of time as they are blanched.
Drain thoroughly and freeze.
How long do I blanch my vegetables?
The University Extension Guide, Quality for Keeps: Freezing Vegetables (GH 1503), gives more specific directions along with approximate yields of frozen vegetables from the fresh quantity, a timetable for cooking frozen vegetables, and blanching instructions for a variety of vegetables from asparagus to zucchini. Copies are available at your local extension center or you can view online at: http://extension.missouri.edu/publications/DisplayPub.aspx?P=GH1503
Here are blanching times for some vegetables. The times listed are for blanching in boiling water. I keep a similar list slipped inside my cupboard for a handy reference.
- 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 the ear, 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.
- Corn on the cob to cut for cream style corn, 4 minutes-cool and cut from ear, scraping the cobs.
- Greens like spinach, 2 minutes
- Shelled Peas, 1½ minutes
- Snow or Sugar Snap Peas, 2-3 minutes
- Summer Squash like zucchini, slices or chunks, 3 minutes; grated, 1-2 minutes.
Last Updated: 6/30/2009