Blanching
Blanching is a quick cooking method where food is dropped into boiling water (or sometimes steam) for a short time, then immediately cooled in ice water, a step called shocking. It brightens colour, partly cooks vegetables while keeping them crisp, loosens skins on tomatoes and peaches, and prepares produce for freezing.
What blanching does
Brightens green vegetables. Raw green vegetables have tiny air pockets between their cells that scatter light and make them look dull. Hot water drives that air out, so you see the green chlorophyll more clearly. That vivid colour appears within the first 30–60 seconds.
Stops enzymes. Plant enzymes keep working after harvest, even in the freezer, causing off flavours, colour loss and toughness. Heating vegetables through to about 80–90 °C / 175–195 °F inactivates most of them.
Softens slightly. Heat begins breaking down pectin in cell walls, turning raw vegetables tender-crisp.
Loosens skins. 30–60 seconds in boiling water makes the skin of tomatoes, peaches and almonds slip off easily.
Why the ice bath matters
Vegetables keep cooking from stored heat after you drain them. Long, slow cooking also lets acids escape from the cells and dull chlorophyll to olive-green. Plunging food into ice water stops all of that in seconds. Leave it in the ice bath for about as long as it boiled, then drain well.
Blanching times
| Vegetable | Time in boiling water |
|---|---|
| Peas, spinach, leafy greens | 30 s–1.5 min |
| Asparagus (medium) | 2–3 min |
| Green beans | 2–3 min |
| Broccoli and cauliflower florets | 2–3 min |
| Carrots (sliced) | 2–3 min |
| Corn on the cob (for freezing) | 7–11 min |
| Tomatoes or peaches (to peel) | 30–60 s |
How to blanch well
- Use plenty of water: about 4 litres per 450 g (1 gallon per lb) of vegetables so the boil doesn't stop.
- Bring it to a full, rolling boil at 100 °C / 212 °F before adding food.
- Work in batches; if the water stops boiling for more than a minute, add less next time.
- Prepare an ice bath beforehand: half ice, half water.
- Start timing once the water returns to a boil.
Blanching vs parboiling
They're close cousins. Blanching is very brief and usually followed by shocking. Parboiling cooks longer, part-way through, so food can finish another way, like potatoes before roasting.
Questions
Why do you blanch vegetables before freezing?
Blanching inactivates enzymes that would otherwise slowly break down colour, flavour, texture and vitamins in the freezer. Unblanched vegetables often turn dull, tough or off-tasting within weeks.
How long do you blanch green beans?
About 2–3 minutes in rapidly boiling water, then straight into ice water for the same amount of time. For freezing, 3 minutes is the usual guideline.
Do you need an ice bath when blanching?
Yes, for crisp vegetables. The ice bath, or shocking, stops cooking immediately so the vegetables don't keep softening and losing colour from their own heat.
Should you salt blanching water?
Salting seasons vegetables from the inside. Around 10–20 g per litre (roughly 2–4 tsp table salt) works well; you don't need it to taste like the sea.