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Canning and Preserving Tips: Why Blanch?

Why blanch vegetables before freezing? Blanching vegetables before freezing is critical to quality, but not safety. Blanching is scalding vegetables in boiling water or steam for a short time. It is typically followed by quick, thorough cooling in very cold or ice water. Blanching stops enzyme actions which otherwise cause a loss of flavor, color, and texture. In addition, blanching removes some surface dirt and microorganisms, brightens color, and helps slow vitamin losses. It also wilts greens, softens some vegetables, such as broccoli and asparagus, and makes them easier to pack. It is critical to use the correct blanching time for the size and type of vegetable (see table below). Under-blanching stimulates enzyme activity and is worse than not blanching. Over-blanching leads to partial cooking and causes loss of flavor, color, vitamins, and minerals.

Green beans before blanching. Blanching vegetables before freezing, helps them to retain their color.

Green beans before blanching. Blanching vegetables before freezing, helps them to retain their color.
Adair Hoover, ©2019 HGIC, Clemson Extension

For home freezing, the most satisfactory way to blanch all vegetables is in boiling water. General instructions for water blanching are as follow:

  1. Use a blancher with a blanching basket and cover or fit a wire basket into a large pot with a lid.
  2. Use one-gallon of water per pound of prepared vegetables.
  3. Put vegetables in a blanching basket and lower into vigorously boiling water. Place lid on blancher. The water should return to boiling within 1 minute or too many vegetables are being used for the amount of boiling water.
  4. Start counting blanching time as soon as the water returns to a boil.
  5. Keep heat high for the time given in the directions for the vegetable you are freezing.
  6. Immediately plunge basket of vegetables into a large quantity of cold water, 60 °F or below.
  7. Change water frequently or use cold running water or ice water. If ice is used, about one pound of ice is needed for each pound of vegetable.
  8. Cooling vegetables should take the same amount of time as blanching.
  9. Drain vegetables thoroughly after cooling. Extra moisture can cause a loss of quality when vegetables are frozen.

Guide to Blanching Vegetables for Freezing.

Vegetable Water Blanching Time (minutes) Vegetable Water Blanching

Time (minutes)

Artichoke-Globe
(Hearts)
7 Collard Greens
All Other Greens
3
2
Asparagus

Small Stalk
Medium Stalk
Large Stalk

 

2
3
4

Kohlrabi

Whole
Cubes

 

3
1

Beans-Snap, Green, or Wax 3 Okra

Small Pods
Large Pods

 

3
4

Beans-Lima, Butter, or Pinto

Small
Medium
Large

 

2
3
4

Onions (blanch until center is heated) Rings 3-7
10-15 seconds
Broccoli (flowerets 1½ inches across) 3 Peas-Edible Pod 1½-3
Brussel Sprouts

Small Heads
Medium Heads
Large Heads

 

3
4
5

Peas-Field (blackeye) 2
Cabbage or Chinese Cabbage (shredded) Peas-Green
Carrots- Small
Carrots-Diced, Sliced or Lengthwise Strips
5
2
Peppers-Sweet

Halves
Strips or Rings

 

3
2

Cauliflower
(flowerets, 1 in across)
3 Potatoes-Irish (New) 3-5
Corn-on-the-cob

Small Ears
Medium Ears
Large Ears

Whole Kernel or Cream Style Corn (blanched before cutting corn off cob)

 

7
9
11

4

Turnips or Parsnips
Cubed
2
From “So Easy to Preserve”, pages 267-268.

Steam blanching is applicable to broccoli, pumpkin, sweet potatoes, and winter squash; however, blanching with either steam or boiling water works satisfactorily. Steam blanching takes about 1½ times longer than water blanching. For more details, please see the references below.

Sources:

  1. Andress, E.L. and J.H. Harrison. 2006. So Easy to Preserve, 5th edition. Bulletin 989, Cooperative Extension Service, The University of Georgia, Athens.
  2. National Center for Home Food Preservation. How do I…Freeze. Blanching Vegetables.http://nchfp.uga.edu/how/freeze/blanching.html
  3. Clemson Home & Garden Information Center fact sheets, HGIC 3060, Freezing Basics, HGIC 3063, Freezing Fruits & Vegetables, and HGIC 3067, Freezing Fruits, Step By Step.

If this document didn’t answer your questions, please contact HGIC at hgic@clemson.edu or 1-888-656-9988.

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