Tier 4 · Wet Heat

TO BLANCH

A brief plunge into boiling water, usually followed by ice water, to set colour, loosen skins, or stop a process before it starts.

Why it works

Blanching does several unrelated jobs and it is worth knowing which one you are doing. It sets green colour: brief heat drives out the gas trapped between cell walls that dulls chlorophyll, so the green brightens — and prolonged heat then degrades that same chlorophyll to olive, which is why the window is short. It deactivates enzymes, particularly the ones responsible for off-flavours and texture loss in frozen vegetables, which is why blanching before freezing genuinely matters. It loosens skins on tomatoes, peaches and almonds by expanding the flesh just beneath and breaking the bond. And it removes harshness from bitter greens and raw onion. The ice bath is not optional in most of these — residual heat keeps cooking the vegetable for minutes, and without shocking, a perfectly blanched vegetable overcooks in the colander.

How to tell

• Green vegetables go visibly brighter within thirty to sixty seconds. That flash of colour is the endpoint for colour-setting.
• Scored tomato skins curl back at the cut, usually in fifteen to thirty seconds.
• The water should return to a boil quickly; if it does not, too much has gone in at once.
• After shocking, the vegetable is cold all the way through — not cool on the outside.

When it goes wrong

Vegetables are olive green and limp.

Left too long. The same heat that brightens chlorophyll destroys it, and the transition is quick.

Blanched vegetables kept cooking and went soft.

Not shocked, or shocked in water that was not cold enough. Carryover in a hot dense vegetable is significant.

Tomatoes are cooked and mushy rather than just peelable.

Far too long. Blanching for skins is measured in seconds, not minutes.

Frozen vegetables taste stale and off after a few months.

Not blanched before freezing. Enzymes continue working slowly even at −18°C; a brief heat treatment deactivates them.

Recovering it

Over-blanched vegetables cannot regain colour or bite; they belong in a soup or a purée. Under-blanched is easy — back in for another twenty seconds. If the ice bath was skipped and things went soft, there is no fix, but the habit is cheap: set the bowl of iced water up before the pot goes on, not after.

Where to practise it

It carries to

Recipes using it

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