A brief plunge into boiling water, usually followed by ice water, to set colour, loosen skins, or stop a process before it starts.
Technique at a glance
A compact visual model of the lesson. Use the full mechanism and success criteria below when you practice.
Concept
A brief plunge into boiling water, usually followed by ice water, to set colour, loosen skins, or stop a process before it starts.
What changes
Blanching does several unrelated jobs and it is worth knowing which one you are doing.
What good looks like
Green vegetables go visibly brighter within thirty to sixty seconds. That flash of colour is the endpoint for colour-setting.
Practice counts when you cook
Reading this brief does not change your School state. Finish a real practice dish in Cook mode and log the cook; that cook is the evidence that advances the skill.
What to focus on
Mechanism
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.
Success criteria
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.
Failure guards
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.