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Freezing
Freezing — kept by cold. How the method works, the ratios and temperatures that make it safe, the steps in order, what it costs in nutrients, and the classic Nordic practice.
How it works
At −18 °C nearly all the water in the food is locked up as ice, so bacteria, yeasts and moulds have nothing to grow in. Nothing is killed. The same organisms restart the moment the food thaws, which is why thawed food is handled exactly like fresh food and not like a preserve. Two things do continue slowly in a freezer: the plant enzymes that ripened the vegetable keep degrading its colour and flavour, and oxygen keeps oxidising the fat. Blanching deals with the first, airtight packing with the second. That is the whole of freezing technique.
How long it keeps
Microbiologically safe indefinitely at a steady −18 °C. Eating quality is the real limit: 3–6 months for oily fish and anything fried, 8–12 months for most vegetables, fruit and lean meat.
The numbers
| Figure | Value |
|---|---|
| Freezer temperature | −18 °C or colder |
| Green beans, blanch | 3 minutes in boiling water |
| Shelled peas, blanch | 1.5 minutes |
| Sliced or diced carrot, blanch | 2 minutes |
| Broccoli or cauliflower florets, blanch | 3 minutes |
| Leafy greens, blanch | 2 minutes |
| Steam blanching | about one and a half times the boiling-water time |
| Headspace for liquids | 2–3 cm — water expands as it freezes |
| Insect eggs in dried food | killed by at least 48 hours at −18 °C |
How to do it
- Pick or buy at the peak and freeze the same day. Every hour at room temperature is quality you cannot get back.
- Blanch the vegetables that need it: into fast-boiling water, timed from the moment the water returns to the boil, then straight into ice water for the same number of minutes.
- Drain hard. Water left on the surface becomes ice, and ice becomes freezer burn.
- Open-freeze anything you want loose — berries, beans, meatballs — spread on a tray, then bag once solid.
- Pack airtight in portions you will actually use, press the air out, label with the contents and the date.
- Freeze in small batches against the coldest wall of the freezer, not as one large warm block.
What makes it safe
- Freezing does not kill bacteria. Treat thawed food as fresh food with its clock already running.
- Thaw in the fridge, in cold water or in the microwave — never on the counter.
- Food that thawed in the fridge and stayed cold can be refrozen; it will be softer. Food that reached room temperature should not be.
- A freezer that has been off long enough for the packets to soften has stopped being a preserve.
Where it goes wrong
- Freezing raw high-water vegetables — cucumber, lettuce, radish — that collapse to mush when the ice crystals rupture their cells.
- Overfilling jars or bottles: water expands by about a tenth as it freezes and glass will crack without headspace.
- Bags with air in them: freezer burn is water subliming out of the food and re-freezing on the packet.
- Freezing hot food, which warms everything around it.
What it costs in nutrients
| Nutrient | Survives the method |
|---|---|
| Vitamin C | Good |
| B vitamins | Good |
| Vitamin A and carotenoids | High |
| Minerals and fibre | High |
The loss in freezing is almost entirely in the blanching water, not in the freezer: vitamin C and the B vitamins are water-soluble and leach out. Carotenoids, vitamin E, minerals and fibre stay where they are. Frozen produce picked ripe and frozen the same day often tests better than "fresh" produce that has spent a week in transport.
The Nordic tradition
In practice the northern freezer is a berry archive. Bilberries, lingonberries, raspberries and blackcurrants all freeze loose on a tray with no sugar and no blanching, and come out good enough for porridge, kissel or a January jam. Chanterelles are the local exception to "just freeze it": they turn rubbery frozen raw, so they are dry-fried in a hot pan until their water has gone, cooled, and frozen in portions. Game and lake fish are frozen in vacuum bags or in a block of ice, which keeps the air off better than any wrapping.
Which foods suit it
| Food | Verdict | Why |
|---|---|---|
| Pumpkin and winter squash | Best | Roast or steam, purée, cool and freeze in portions. This is the answer to the purée problem. |
| Green beans | Best | Top and tail, cut to length, blanch exactly 3 minutes, ice-water immediately, drain hard, bag. |
| Peas | Best | Pod, blanch shelled peas 1.5 minutes, ice-water, drain and freeze loose on a tray. |
| Rhubarb | Best | Wash, chop into pieces, freeze raw on a tray. No blanching, no sugar, no fuss. |
| Strawberry | Best | Hull, dry, open-freeze on a tray, bag once solid. No sugar needed. |
| Raspberry | Best | Open-freeze on a tray without washing if they are garden-clean. They hold their shape remarkably well. |
| Blackcurrant | Best | Strig or not, open-freeze on a tray. Keeps the vitamin C better than any heated method. |
| Lingonberry | Best | They freeze loose and perfectly, with no sugar and no preparation beyond picking out the leaves. |
| Sea buckthorn | Best | Cut whole small branches, freeze them, then knock or shake the frozen berries off cleanly. The traditional and easiest harvest. |
| Bilberry and blueberry | Best | Open-freeze clean, dry berries on a tray. No sugar, no blanching, no preparation at all. |
| Herbs | Best | For soft herbs: chopped into ice-cube trays with water or oil, or simply bagged flat and crumbled frozen. |
| Baltic herring | Best | Cleaned and gutted, frozen fast. Also the step that deals with parasites for anything to be eaten raw or lightly cured. |
| Tomato | Good | Freeze whole and raw in bags. The skins slip off under warm water as they thaw — no blanching needed. |
| Beetroot | Good | Cook fully first — beetroot does not freeze well raw — then peel, slice and freeze. |
| Carrot | Good | Blanch sliced or diced carrot for 2 minutes, small whole carrots for 5, chill in ice water, drain hard, freeze. |
| Onion | Good | Chop and freeze raw, no blanching needed. They go soft, which does not matter for cooking. |
| Garlic | Good | Peeled cloves or a paste freeze well and lose only a little of their bite. |
| Wild mushrooms | Good | Dry-fry in a hot pan until the water has gone, cool, then freeze in portions. Never freeze raw chanterelles. |
| Apple | Good | Slices tossed with lemon or ascorbic acid, open-frozen. Or freeze cooked purée, which takes less space. |
| Plum | Good | Halve, stone and open-freeze. Better than freezing whole, which makes the stone impossible to remove later. |
| Cabbage | OK | Blanch wedges 3 minutes or shredded cabbage 1.5 minutes. The texture goes soft — this is soup and stew cabbage. |
| Cucumber | No | Raw cucumber cells collapse completely on thawing. What comes out is grey water. |
Safety rules, temperatures, blanching times, headspace and the pH 4.6 line: USDA Complete Guide to Home Canning and the National Center for Home Food Preservation guidance (US Government / land-grant publications, public domain). Acidity classes: the FDA's published approximate-pH tables. Jam composition: Directive 2001/113/EC. Fish freezing before raw or lightly cured use: Regulation (EC) No 853/2004, Annex III. Checked 2026-09-06.
Sources for this method
- USDA and NCHFP freezing guidance (public domain)
- Regulation (EC) No 853/2004, Annex III — parasite treatment of fishery products
Frequently asked questions
Do I have to blanch vegetables before freezing?
For most of them, yes. Unblanched beans, peas, broccoli and greens keep the enzymes that make them taste of hay after a couple of months. Onions, peppers, chopped herbs and berries need no blanching at all — they have little of the enzyme in question, or you will cook them anyway.
Can I refreeze food that has thawed?
If it thawed in the refrigerator and stayed cold throughout, yes — it is safe, and it will be softer than it was. If it reached room temperature, do not refreeze it; cook it now or throw it out.
Why do my berries freeze into one solid lump?
Because they went into the bag wet and touching. Spread them in a single layer on a tray, freeze until hard, and only then bag them. They will pour like gravel for a year.
Does freezing kill parasites?
It can, given a low enough temperature for long enough. EU food-hygiene rules require fish intended to be eaten raw or only lightly salted, marinated or cold-smoked to be frozen throughout at −20 °C for at least 24 hours (or −35 °C for 15 hours). A domestic freezer at −18 °C is close to but not at that figure.
The other methods
All methods compared
The ten hurdles, and the foods each one suits.
Drying
The oldest method, and the only one that needs no cold, no jars and no electricity once it is done. It works by taking the water away rather than by making the food hostile.
Fermenting
The method that makes its own preservative. Salt buys time for lactic acid bacteria, and the acid they produce is what keeps the jar.
Pickling in vinegar
Fast, repeatable and completely different from fermenting: here you add the acid instead of growing it, so the jar is as safe as the vinegar you used.
A pantry you can see
TempoLife tracks the food you logged fresh and the jars you put down in autumn, so the batch numbers on the lids match the calendar.