Food preservation

Botulism is rare, and it is rare because these rules are followed. When they are not, it kills whole families at a single meal: the toxin paralyses from the head downward — double vision, drooping eyelids, slurred speech, difficulty swallowing, then the breathing muscles — 12 to 36 hours after eating, sometimes days.

1. Low-acid foods sealed without oxygen need 116–121 °C. Vegetables, meat, fish, beans, soups and stocks in jars or cans must be processed in a pressure canner at 10–15 psi (0.7–1 bar). A boiling-water bath reaches 100 °C and does not kill the spores — it creates exactly the sealed, oxygen-free jar they grow in.
2. Acid foods can be water-bath canned. Most fruit, jams, and vegetables pickled in vinegar of at least 5% acidity are below pH 4.6. Tomatoes sit close to the line — add acid: 1 tablespoon of lemon juice or ¼ teaspoon of citric acid per 500 ml jar.
3. Never store garlic, herbs or vegetables under oil at room temperature. Oil excludes air. Refrigerate it and use it within about 4 days, or acidify it first.
4. No honey for babies under 12 months. Honey can carry spores that an infant's gut lets grow.
5. Discard any sealed container that is bulging, leaking, spurting, foaming, or smells wrong — unopened, and without tasting. But know that toxin can also be present with no sign at all, which is why rule 1 is the real protection.
6. If a home-canned low-acid food is in doubt, boil it before tasting. The toxin — not the spores — is destroyed by heating the food right through to above 85 °C for at least 5 minutes. Boiling for 10 minutes covers it with margin.

Choose by the food, the climate and what you have — and understand which lever each method pulls, because that tells you how it fails.

Drying works when food loses water faster than organisms can grow in it. Three things drive it: warm air, dry air, and moving air — and moving air matters most.

Conditions: air above about 30 °C and below about 60% relative humidity, with a breeze. In humid climates, sun drying fails and food has to be dried over a fire or in a smokehouse, where the heat drives the humidity down.

Preparation:

• Slice thin and even — 3–6 mm for fruit and vegetables, 5 mm for meat strips. Thick pieces case-harden: the outside seals while the inside stays wet and rots.
• Meat: cut across the fat and trim it off. Fat does not dry; it goes rancid.
• Meat must be heated before or after drying to kill pathogens that drying alone does not: beef and game to an internal 71 °C, poultry to 74 °C. Traditional jerky made without this step has caused E. coli and Salmonella outbreaks.
• Fish: small fish under a hand's length dry whole; larger fish are split flat along the backbone, the flesh scored, and salted first. See the fishing guide.
• Blanch most vegetables — dip in boiling water 2–4 minutes — to stop the enzymes that brown them and destroy vitamins in storage.

When it is done:

| Food | Test | |---|---| | Meat jerky | Bends and cracks without snapping, no moisture beads when squeezed | | Fruit | Leathery and pliable; tear a piece and press — no moisture appears | | Vegetables | Brittle or crisp | | Fish | Firm right through; no soft core when pressed at the thickest point |

Store dried food in sealed containers in the dark. It reabsorbs water from damp air within days. Condition fruit first: pack it loosely in a jar for a week, shaking daily; if moisture appears on the glass, dry it further.

Salt preserves by pulling water out of cells and binding what remains so that bacteria cannot use it. It is also why salt was money for most of history: it was the refrigerator.

Dry salting. Pack the food in salt, in layers, with salt between every layer and over the top. For fish, roughly 1 part salt to 3 parts fish by weight for a hard cure. The salt pulls out liquid that forms a brine; for a dry cure, drain it off; for a wet cure, keep the food submerged in it. Then dry. Salt cod — split, salted, and air-dried — keeps for years and must be soaked in several changes of water over 24–48 hours before cooking.

Brining. A saturated brine is 26% salt by weight — about 360 g of salt dissolved per litre of water, and it will dissolve no more. Most brining for storage uses a strong brine near saturation, kept cool.

Smoking has two meanings, and confusing them is the danger:

• Cold smoking keeps the smoke below about 30 °C. It flavours and dries the surface. It does not cook, and it does not preserve on its own — the food must be properly salted first, and cold-smoked meat and fish are still raw.
• Hot smoking cooks as it smokes. Fish should reach an internal temperature of at least 63 °C for 30 minutes. It keeps days to weeks, not months, unless it is also dried hard.

Curing salts. Commercial cured sausages and hams are made with nitrite (curing salt), which specifically blocks botulism in dense meat where oxygen cannot reach. Traditional saltpetre did the same, unreliably. A dense sausage or whole ham cured with plain salt alone, and not dried properly, is a botulism risk.

Salt the vegetables enough that spoilage organisms struggle, keep out the air, and the lactic acid bacteria already on every cabbage leaf win the race — turning sugar into acid until the pH is below 4, where almost nothing else survives.

Sauerkraut, by the numbers:

1. Shred firm cabbage finely.
2. Weigh it, and add 2–2.5% of that weight in salt — 20–25 g of salt per kg of cabbage. Use plain salt; iodine and anti-caking agents can inhibit the bacteria.
3. Massage and pound until the cabbage releases its own water — 5–10 minutes.
4. Pack it hard into a crock or jar, pressing out air pockets, until the brine rises above the cabbage. If there is not enough after a few hours, top up with a 2% brine (20 g salt per litre of water).
5. Weight it down so every shred stays under the brine. Anything exposed to air moulds.
6. Cover against dust and insects but let gas escape.
7. Ferment at 18–22 °C for 3–6 weeks. Warmer ferments faster and softer; above about 24 °C it can go soft and spoil. Cooler is slower and better.
8. Done when it tastes sharply sour and no longer tastes of salt. Move it somewhere cold, where it keeps for months.

The same method, with the same 2–3% salt, works for cucumbers, turnips, carrots, beans and most firm vegetables.

A root cellar is a controlled climate: cool, humid, dark and ventilated. The build is in the root cellar. What matters here is that crops do not want the same conditions, and several actively damage each other.

Stored grain fails in two ways: insects eat it, or mould grows in it. Both are controlled by moisture, and the threshold is sharp: cereal grain stored below about 13% moisture keeps; above it, it heats, moulds and sprouts.

The salt test tells you roughly where you are without instruments. Put a handful of completely dry salt in a dry glass jar with a few handfuls of grain, seal it, shake for a minute, and leave it 15 minutes. If salt sticks to the glass or clumps, the grain is above about 15% moisture — dry it further in the sun, spread thin and turned, before storing.

Hermetic storage kills insects without chemicals. Grain sealed airtight — in a sealed drum, a clay pot sealed with mud, or a triple-layer plastic sack — uses up its own oxygen as the insects and grain respire, and the insects die within weeks. It only works on dry grain; damp grain in a sealed container moulds.

Aflatoxin is the hazard that matters most. Aspergillus moulds growing on damp-stored maize and groundnuts produce aflatoxins: a potent liver carcinogen over years, and acutely lethal in large doses — a 2004 outbreak in Kenya from home-stored maize killed 125 people. Aflatoxin survives cooking.

• Dry the crop quickly after harvest.
• Sort out any discoloured, shrivelled or mouldy kernels before storing and before cooking.
• Never eat or feed to animals grain that is visibly mouldy. Feeding it to livestock puts aflatoxin into milk.
• Store off the ground, in a dry, ventilated place, protected from rats. See the granary build.