Blanching
Holding vegetables briefly in boiling water, then straight into iced water. Colour, texture and enzymes are all settled on that short trip between two temperatures.
The mechanism
When green vegetables hit boiling water the air between their cells escapes and the chlorophyll shows more clearly, which is why the colour brightens in the first minute or two. At the same time the enzymes that would slowly brown the vegetable and spoil its taste are knocked out above 80 °C; that is the real reason to blanch anything headed for the freezer. Leave it too long and heat plus the vegetable’s own acid turn chlorophyll olive, while pectin in the cell walls dissolves and the texture slackens. Iced water stops all of it within seconds. Keep at least five parts water to one of vegetable, or the cold load drops the pot below the boil and the timing slips.
The thresholds that define it
“Medium heat” is not a technique. Every line below is a point where something starts or stops.
- 100 °C The water must be at a full boil, and should return to it within 30 seconds of the vegetables going in.
- 80 °C Where the enzymes are knocked out; the goal of blanching before freezing.
- 1–3 dakika Typical time for beans, peas and spinach; broccoli 2–3 minutes.
- 0–4 °C The ice bath. The vegetable stays in no longer than it was boiled.
- 5 : 1 Minimum ratio of water to vegetable.
How to read it by hand
Watch the colour: the moment the green jumps to a bright, living shade, fish one out and bite it. A slight resistance to the tooth means it is time for the strainer and the ice. If you cannot keep your hand in the ice bath for more than a few seconds, it is cold enough.
The three mistakes people make
01 The vegetables went a greyish olive ⌄
Why
Boiled too long or with the lid on, so volatile acids fell back and dulled the chlorophyll.
What to do
Blanch with the lid off, cap it at 3 minutes and go straight to ice.
02 Frozen vegetables faded and smelt of hay within months ⌄
Why
The blanch was skipped; the enzymes kept working slowly even in the freezer.
What to do
Blanch above 80 °C for at least a minute before freezing.
Where it comes from
In Anatolian kitchens preparing for winter, green beans and okra were briefly boiled before being strung up to dry. When home freezers spread the same step moved to peas and spinach bound for the freezer bag; the method did not change, only where the food was headed.
Giving the heat another way
Deep frying
Surface water flashes to steam and pushes outward — that is the shield keeping oil out. Cold oil never builds it, and the food drinks the fat instead.
The oven
Air carries heat badly, so a 200 °C oven does not make 200 °C food. The inside stays where water boils, at 100 °C.
Boiling & poaching
Water cannot pass 100 °C, so turning the flame up changes nothing. Boiling is set by time and salt, not by temperature.