Even after you pick your crops, enzymes continue to break down the nutrients, convert sugars to starches, and generally degrade flavor and texture. Blanching with steam or boiling water stops this action and preserves fresh-picked color. Tests have shown that, after nine months, vegetables that were blanched before freezing retain up to 1,300 percent more vitamin C and other nutrients than vegetables frozen without blanching.
Steam blanching does the best job of preserving color, flavor, nutrition, and texture, says H. William Schafer, Ph.D., an extension food technologist with the University of Minnesota. Water blanching tends to leach out water-soluble vitamins. Soaking vegetables to clean them can also literally wash away nutrients; better to rinse and brush them quickly under cold running water. Water blanching is more effective at getting rid of yeasts, molds, and bacteria if they are present and for removing cabbageworms from cauliflower and broccoli. With either method, timing is key. Under-blanching can actually encourage quality-zapping enzymes.
- Clean and chop vegetables as if using them right away.
- Add 1 to 2 inches of water to a pot and bring to a boil. Using a basket or loose cheesecloth, suspend a layer of the prepared vegetables just over the boiling water, and cover.
- When steam begins to escape, start timing. Halfway through the blanching process, check to make sure the vegetables are not clumping together and that they are cooking evenly.
- Remove, cool, dry, and pack.
- Weigh prepared vegetables to make 1-pound portions.
- Boil 1 gallon of water in a large kettle.
- Place vegetables in a mesh or blanching basket and set in the boiling water. Start timing when water returns to boil.
Remove, cool, dry, and pack.
Take the Plunge
"The quicker you cool vegetables after blanching, the more color, texture, and flavor you will retain," says Dr. Schafer. Cool them for about the same amount of time they were blanched (twice as long for corn on the cob). Use the ice bath method (pictured) or place vegetable pieces in a container and set that container in a larger container filled with ice water. To prevent ice buildup on the vegetables once they're in the freezer, dry them before packing. Spread paper towels over cloth towels and place the blanched vegetables on top. A table fan will help speed drying.
Pack It Up
To keep vegetable pieces from freezing together, some people spread them out on trays and freeze them before packing them into bags. This is called tray packing. For most vegetables, this is not necessary, though it does help with fruit and certain crops such as peas, corn (off the cob), and beans. For most other vegetables, just pack pieces as tightly as possible into freezer containers or bags (pressing or sucking excess air out of the bags), date them, and freeze them. Be sure your freezer is set at 0°F or cooler; higher temperatures will decrease their shelf life, Dr. Schafer says. "Oxygen-bearing packets and freeze-thaw cyclings also have negative effects on quality and can accelerate some nutrient loss."
While most vegetables will keep 12 to 18 months in the freezer, plan to use them by the time your next crop is ready for the picking!
Cucumbers, lettuce, tomatoes, watermelon, and other vegetables that contain a lot of water or have a delicate cell structure do not freeze well. You can puree, then freeze tomatoes.
Best Bets for Freezing and Blanching Times
|Vegetable||Quantity (yields 1 pint)||Blanching time (minutes)*|
|Asparagus||1 to 1 1/2 lbs||2 (small), 3 (medium), 4 (large)|
|Beans (snap, green, wax)||3/4 to 1 lb||3|
|Beets||1 1/4 to 1 1/2 lbs||Until tender, then slice or dice|
|Brussels sprouts||1 lb||3 (small), 4 (medium), 5 (large)|
|Carrots||1 1/4 to 1 1/2 lbs||2 (sliced or diced), 5 (small whole)|
|Cauliflower||1 1/4 lbs||3|
|Corn on the cob||6 to 8 ears||7 (small), 9 (medium), 11 (large)|
|Eggplant||1 to 1 1/2 lbs||4|
|Peas (snap or snow)||2 to 2 1/2 lbs||1 1/2 (small), 2 (large)|
|Peppers (sweet or bell)||3/4 lb||2 (strips, rings), 3 (halves)|
*For steam blanching, multiply suggested time by 1.5.