What is Blanching?

Blanching vegetables before freezing or dehydrating ensures a high-quality end product.

Summer 2020 is over, and while most of us won’t be sorry to see this year behind us, harvesting the last of the garden always makes me a bit wistful. But harvest we must, and quickly – before freezing temperatures hit. With the shortage of canning supplies, you may be planning to freeze or dehydrate more vegetables than usual. These food preservation techniques are a little different from canning, and often require blanching. But what is blanching? When do we need to blanch vegetables? And why do we need to blanch?

Boiling Water or Steam Blanching

Blanching is basically the process of submerging raw vegetables into either boiling water or steam for a certain period of time, then quickly submerging the same vegetables into ice water.

Most, but not all, raw vegetables need to be blanched before freezing or dehydrating. Corn, carrots, potatoes, winter squash, and hearty greens like chard should be blanched. To blanch:

  • Wash and prepare vegetables. i.e. shell peas, peel and slice beets and carrots, tear greens into large pieces.
  • Boil water in a large pot.
  • Prepare another large pot with ice water.
  • Submerge raw vegetables in the boiling water. Let water return to boil for the indicated time.
  • Drain and submerge into the ice water to cool.
  • Drain and spread vegetables on trays to freeze or dehydrate.

You will find blanching tables in most food preservation books like the Ball Blue Book or So Easy to Preserve. The blanching period for individual vegetables is the same whether you plan to freeze or dehydrate. For example, sliced potatoes should be blanched for 5-6 minutes, whether you are going to freeze the sliced potatoes or whether you are going to dehydrate the sliced potatoes. But each vegetable has its own perfect blanching period. Collard greens should be blanched for 3 minutes, peas for 2 minutes, and turnip slices for 4 minutes.

Why Blanch Vegetables?

Have you ever picked an ear of corn and then immediately cooked and served it? If so, you know how sweet and fresh it tastes. The same is true for almost anything you pick in the garden and then immediately eat.

On the other hand, corn that you pick this morning and store in the refrigerator will still taste great when you cook it next week, but will not taste as fresh and sweet as the ear you eat today. Once a vegetable is harvested, it starts to age and quality declines. It’s the vegetable version of my sagging skin! Blanching acts like a vegetable face lift. It stops the aging (or enzymatic) process and helps retain quality.

Can you skip the blanching step? Yes. You will still have a safe product (assuming you followed safety guidelines) because both freezing and dehydrating also slow (but don’t stop!) the aging process. But you lose quality while the vegetables are in the process of drying or freezing. Potatoes, winter squash, corn and other light-colored vegetables turn a brownish color if the blanching step is skipped, and they may turn out mushy when they are cooked. Thus, most people find the blanching step is worth the little extra work.

Blanching also provides extra protection against bacteria and insects. The blanching process itself helps to kill pathogens still lurking around after the vegetables have been washed.

Do All Vegetables Have to be Blanched?

Despite my little rant above, not all vegetables need to be blanched before freezing or dehydrating! Some vegetables, like peppers, onions, celery, and delicate greens like spinach don’t need to be blanched. The drying or freezing process itself works well enough to arrest the aging process with these less-sweet vegetables.

Also, if you are dehydrating vegetables that were previously frozen or canned, they do not have to be blanched. This is because the previous method already interrupted the aging process.

Related Posts:

How to Dry Vegetables in the Oven

Make Your Own Vegetable Powders

How to Freeze Garden Peas

by Renee Pottle

Renee Pottle, a freelance writer and Home Economist, is fanatic about all things food. She blogs about canning and food preservation at SeedToPantry.com. Find her professional food writing info at PenandProvisions.com.

September 21, 2020

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