Blanching
ˈblæn·tʃɪŋ
A food preparation method where fruits or vegetables are briefly cooked in boiling water or steam, then immediately cooled in ice water to stop cooking and preserve color, texture and nutrients
Full Explanation
Blanching is a short, controlled heat treatment applied to fruits and vegetables before freezing, canning or drying.
The process has two steps: (1) expose the food to boiling water or steam for a short amount of time (2) immediately plunge it into ice-cold water. This step is called "shocking" to stop the cooking process dead in its tracks. The main purpose is to disable enzymes naturally occurring in the food. Without this step, the enzymes would continue breaking down color, flavor and nutrients.
Blanching can also reduce the bacteria on the food, help loosen skins for easy peeling and remove some pesticide residues.
Timing matters a lot during blanching; too short and the enzymes survive; too long and the food loses nutrients, texture and flavor. Generally (not a rule), about 30 secs to 3 mins for boiling or steaming depending on the food type. Leafy vegetables will take less time and legumes like peanut will need more time.
Why It Matters
Most of the frozen vegetables at the grocery store have been blanched before packaging. Blanching helps you make sense of why some frozen produce holds up better than others. It also helps you store certain vegetables to avoid waste.
Example
If you freeze green beans without blanching, it often comes out of the freezer dull in color, mushy and somewhat bitter. Blanching it for just a minute or two before freezing keeps it vibrantly green, firm and flavorful.
Common Misconceptions
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"Blanching cooks the food". Blanching is a partial intentional pre-treatment. It's not full cooking because the food is barely ready for eating in most cases and is immediately cooled to prevent any further cooking.
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"Blanching destroys nutrients". Some water-soluble vitamins like Vitamin C leach slightly into the blanching water. But research shows blanched frozen vegetables preserve their nutrients better over time than unblanched ones. Because the process stops enzymes that would have degraded nutrients.
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"Blanching and boiling are the same thing". Boiling fully cooks food. Blanching is a brief timed dip followed by immediate cooling. It's different from thorough cooking.