Blanching

Blanching is scalding vegetables in boiling water or steam for a short time. NCHFP: it is a must for almost all vegetables to be frozen, because it stops enzyme actions that cause loss of flavor, color, and texture ¹. It also helps remove dirt and microorganisms, brightens color, retards vitamin loss, and wilts vegetables so they pack more easily.

That is a freezer-prep step. It is not Canning. A blanched bean in a jar on a shelf is still a low-acid moist food.

Time is vegetable-specific; underblanching is worse than skipping #

NCHFP: blanching time is crucial and varies with the vegetable and size. Underblanching stimulates enzymes and is worse than no blanching. Overblanching costs flavor, color, vitamins, and minerals. Follow their recommended times ¹.

Method numbers from that page, not a full table:

• Water blanch: 1 gallon of water per pound of prepared vegetables. The water should return to a boil within 1 minute, or the load is too large. Start counting when the water returns to a boil ¹.
• Steam blanching takes about 1½ times longer than water blanching. Start counting when the lid is on ¹.
• Cool immediately in water at 60°F or below for about as long as you blanched. Drain well; extra moisture hurts frozen quality ¹.

Examples from their water-blanch table: snap beans 3 minutes; green peas 1½ minutes; small asparagus stalks 2 minutes, large 4 minutes ¹. Look the vegetable up. Do not interpolate.

Microwave blanching may not inactivate enzymes; NCHFP does not recommend it as equivalent ¹.

What to notice #

Color should brighten, not go olive and slack. Pieces should be hot through, then cold through. Ice in the cooling water (they suggest about a pound of ice per pound of vegetable if you use ice) is a cooling tool ¹.

NCHFP’s public FAQ gives the same definition — heating or scalding in boiling water or steam for a short period — and says yes, blanch vegetables before freezing ². Blanching also appears as a minor help against surface microbes in canning, but the vital controls there are the researched process ³. See Freezing and Preserving.