Blanch fresh vegetables before freezing

By Lou Ann Jopp, University of Minnesota Extension

ST. PAUL, Minn. (6/15/2009) — Blanching (scalding vegetables in boiling water or steam for a short time) is a must for almost all vegetables to be frozen successfully. It slows or stops the enzyme action which can cause loss of flavor, color and texture.

The blanching time is important and varies with the vegetable and size. Underblanching actually stimulates the activity of enzymes and is worse than no blanching. Overblanching causes loss of flavor, color, vitamins and minerals.

Blanching in the microwave may not be effective, since research shows some enzymes may not be inactivated, which could result in off-flavors and loss of texture and color. Microwave blanching will not save time or energy as it would be necessary to work in small quantities.

Here are a couple of methods that will help you successfully prepare your vegetables for freezing:

Blanching in water

1. Wash, drain, sort, trim and cut vegetables as for cooking fresh.
2. Use one gallon water per pound (approximately 2 cups) of prepared vegetables. Use two gallons water per pound for leafy greens.
3. Bring water to rolling boil.
4. With vegetables in a wire basket, coarse mesh bag or perforated metal strainer, immerse into boiling water.
5. Cover. Water should return to boiling within 1 minute; if not, you are using too much vegetable for the amount of boiling water and the vegetables will become soggy.
6. Start counting blanching time as soon as the water returns to a boil. Keep heat high for the time given for the vegetable you are freezing.
7. Cool immediately in ice water for the same length of time used for blanching. Keep chilling water ice cold. Cooling quickly and thoroughly will stop the cooking process. 
8. Drain vegetables thoroughly. Extra moisture will form ice crystals which cause a loss of quality.
9. Pack vegetables either by dry pack or tray pack. For dry pack, pack vegetables tightly into containers or freezer bags. Press out air and seal tightly. For tray pack, put single layer of vegetable on a shallow pan and freeze. When vegetable is frozen, place in freezer bag or container.  Press out air and seal tightly.
10. Freeze.
11. Frozen vegetables maintain high quality for 12 to 18 months at zero degrees or lower.

Steam blanching
Place one layer of vegetables in a wire basket. Suspend in steamer above several inches of rapidly boiling water and cover. Steam 1 1/2 times longer than boiling water blanch time.

This information comes from the National Center for Home Food Preservation (more information at http://www.uga.edu/nchfp/how/freeze/blanching.html) and University of Minnesota Extension (visit Extension’s food preservation website at http://www.extension.umn.edu/foodsafety/components/foodpreservation.htm).

Any use of this article must include the byline or following credit line:
Lou Ann Jopp is a food science educator with University of Minnesota Extension.

Media Contact: Catherine Dehdashti, U of M Extension (612) 625-0237, ced@umn.edu

URL: http:// www.extension.umn.edu/extensionnews/2009/blanch-freeze-veg.html  This page was updated Mar. 8, 2010 .
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