Food preservation: canning, fermentation & storage

Why preserve food yourself – and how it fits emergency supplies

Preserving makes seasonal harvest and purchases last for months and thus supplements the emergency supply with variety and fresh nutrients. It is a useful addition, but not a substitute for the storable basic supply of canned goods, pasta, rice and water that the government recommends.

Each method works by depriving microorganisms of essentials: water, a suitable pH, heat or oxygen. Which method is safe depends mainly on the acidity of the food – that is the red thread of this guide.

For beginners, freezing, drying, fermenting and sour pickling are the simplest and safest ways. Classic water-bath canning is only safe for acidic foods; with everything else lurks the greatest danger, botulism. Anyone who internalizes this rule has already made the most important step right.

What are the four preservation principles?

All preservation methods use one or more of four principles. Understanding them helps you recognize why a method is safe for a particular food – or why it isn't.

Important: cold and acidity inhibit many germs but do not kill all. The dangerous botulism bacterium survives cold and mild (but not sufficiently acidic) conditions as a spore. Therefore the principles must be combined appropriately to the food.

1. Remove water: salt and sugar bind free water, drying evaporates it – microorganisms find no usable water (water activity drops)
2. Lower pH: acidity (vinegar) or fermentation makes the food acidic – below pH 4.6 the botulism bacterium no longer grows
3. Heat: sufficient heating kills germs – in the home only up to about 100 °C, which is insufficient against botulism spores
4. Remove oxygen and heat: vacuum sealing and cold (cooling, freezing) slow spoilage – but replace neither acidity nor heat

Canning: water bath versus pressure – and the botulism trap

When canning you heat the food in a sealed jar so that a vacuum forms when cooling and the lid seals tightly. The critical point is temperature: a boiling water bath reaches only about 100 °C. This is enough to kill most active germs – but NOT to reliably destroy the heat-resistant spores of Clostridium botulinum.

Therefore the cardinal rule applies: in a water bath you may only can ACIDIC foods – fruit, sour pickles, foods with a pH value of 4.6 or lower. The acidity prevents surviving spores from germinating and producing toxin. LOW-ACID foods – beans, peas, carrots, squash, mushrooms, meat and fish – must NOT be water-bath canned. In the airtight, low-acid jar the bacterium finds exactly the oxygen-free environment it needs to produce toxin.

You can only really kill spores at over 100 °C, practically at about 121 °C under pressure. Only a pressure canner achieves this, which is barely widespread in private households in German-speaking countries. For beginners the safe recommendation therefore is: do not can low-acid vegetables, meat and fish, but freeze them, sour pickle (vinegar lowers pH below 4.6) or ferment them.

Expert tip: never rely on appearance or smell as proof of safety when preserving – botulin toxin is colorless, odorless and tasteless. If you really want to can low-acid food, you cannot get around a tested pressure method or reliable pH measurement (target below 4.6). Merely heating twice to 100 °C reduces risk but does not replace spore inactivation.

How do I recognize botulism when canning?

Botulism is a rare but life-threatening poisoning from the toxin of the bacterium Clostridium botulinum – one of the strongest known poisons. The bacterium thrives only without oxygen, such as in an airtight, low-acid preserve. There it forms its toxin from surviving spores. First signs are often vision problems and double vision, then difficulty swallowing and speaking and progressive paralysis descending from the head up to respiratory paralysis. On suspicion it is an emergency: immediately call ambulance 144 or Tox Info Switzerland 145.

Important to know: cooking destroys the toxin but not the spores. If you heat contaminated food sufficiently – roughly ten minutes at a rolling boil as a guideline – the already-formed toxin becomes harmless. The resistant spores, however, survive this and can form toxin again under improper storage. Heating is therefore not a free pass to unsafely can low-acid food.

You recognize spoiled or dangerous cans by several signs. An important caveat: the toxin itself is not visible, smellable or tasteable. Absence of warning signs is therefore no guarantee – in any doubt: don't taste, throw away.

1. Bulging or swollen lid or puffed-up can (bloating from gas formation)
2. Leaking, spilled or burst jars
3. Liquid or foam that sprays when opening
4. Discoloration, mold or musty, putrid smell
5. Principle "when in doubt throw away": never taste suspicious cans, dispose of contents safely

Fermenting: sauerkraut and sour vegetables

During fermentation, lactic acid bacteria convert the sugar in the vegetable into lactic acid. This lowers the pH, makes the vegetable shelf-stable and digestible – finished sauerkraut is significantly more acidic than the safety threshold of pH 4.6. This low pH, when done correctly, also protects against botulism.

For this to work, the vegetable must be completely submerged in the brine (oxygen-free) and contain enough salt. A proven guideline is a salt content of about 2 to 2.5 percent, so about 20 to 25 grams of salt per kilogram of vegetables. Protection only takes effect when fermentation is complete and pH has reliably dropped below 4.6 – in the first days or with too little salt it is not guaranteed.

1. Finely slice or chop vegetables and mix with about 2–2.5% salt (20–25 g per kg)
2. Knead or pound vigorously until juice releases and layer tightly in clean container
3. Cover vegetables completely with brine and weight down so nothing touches air
4. Let ferment at room temperature, then continue storage cool; discard on off-smell, mold or discoloration

Drying and dehydrating

Drying removes water from food: heat and air circulation lower residual moisture so much that microorganisms barely multiply. Well-suited are fruit, herbs, mushrooms and vegetables. Drying is done gently at low temperature – in the oven about 40 to 50 °C, in air it works from about 30 °C. Higher experienced values up to around 70 °C vary by product; they are guidelines, not officially fixed limits.

For beginners, herbs, apple slices and dried fruit are an easy start. With meat (dried meat, jerky) caution is advised: pure low-temperature drying is microbiologically tricky. Anyone drying meat should stick to tested instructions and take food safety seriously. Finished dried goods are stored airtight, dry and dark.

1. Slice food evenly thin so everything dries at the same rate
2. Dry gently: herbs/air from about 30 °C, fruit and vegetables in oven/dehydrator about 40–50 °C
3. Dry until nothing is still moist or flexible-sticky (minimize residual moisture)
4. Store airtight, dry and dark; discard on moisture traces or mold

How long do stored provisions keep? (Guidelines)

How long unopened emergency supplies keep depends mainly on their fat content: the lower fat an food, the longer it keeps. Ground and refined varieties – white rice, white flour, light pasta – often exceed their best-by date by months or years. Whole grain varieties contain natural fat from the germ and bran, which oxidizes and becomes rancid; they keep much shorter (whole wheat flour about 4-6 months, brown rice months to about one year).

Canned goods keep differently depending on acid content: acidic (fruit, tomatoes, pickled) about 12-18 months in best quality, non-acidic (meat, fish, vegetables) about 2-5 years – both if the can is intact. Sugar, salt and honey practically don't spoil if stored dry; clumping or crystallizing isn't spoilage. Dried legumes keep 1-2 years but become harder over time and then require longer cooking.

Store supplies optimally constantly cool at about 15-20 °C, dark, dry and tightly sealed – away from the stove, dishwasher, refrigerator and windows. Important: these periods are rough guidelines from consumer and official sources (among others from Germany and the USA), not official Swiss requirements. Swiss authorities mention only principles like «cool, dry, dark» and rotation. When in doubt, rely on your sensory test and the rule « when in doubt, throw it out ».

Vacuum sealing: what it can and cannot do

Vacuum sealing removes air from packaging. This slows oxidation and growth of oxygen-requiring germs and thus extends shelf life in the refrigerator or freezer. Vacuum sealing does not kill germs and is not a substitute for cooling or heating.

Crucial for safety: the oxygen-poor environment can even favor anaerobic germs like Clostridium botulinum. Vacuum-sealed food must therefore remain refrigerated or frozen – never store as sole preservation at room temperature. Vacuum sealing is an addition to the cold chain, not independent preservation.

Freezing, storage and rotation

Freezing at −18 °C stops the multiplication of microorganisms almost completely, but does not kill them. After thawing, surviving germs become active again and multiply like on fresh food – use thawed goods promptly and do not carelessly refreeze. During prolonged power outage frozen goods thaw; how to handle this is covered in our power outage scenario.

All supplies – purchased and home-made – are stored cool, dry and protected from light. Use older items first and place new items at the back ("first in, first out") so nothing quietly goes past date. A simple, if not officially required practical tip: label homemade preserved goods with contents and date.

With purchased products the date helps: the best-by date ("best before") is a quality statement – much is still edible afterward. The expiry date ("use by") is on easily perishable foods and is safety-relevant: you should not eat the product after this date.

1. Freeze at −18 °C; portioned and labeled so nothing unknown is in the freezer
2. Use thawed items promptly and do not carelessly refreeze
3. Store supplies cool, dry and dark and regularly check date and damage
4. Rotate by "first in, first out": use older first, place new ones at the back

Small self-sufficiency: sprouts and garden

A garden or balcony provides fresh vegetables in summer and autumn that you can then preserve. Realistically speaking, home growing is a welcome supplement – no complete substitute for a storable supply and no survival promise. The official Swiss emergency supply deliberately relies on storable foods and water.

Sprouts and shoots provide fresh vitamins within days with just water and can be stored as dry seeds for a long time. Safety note: sprouts grow warm-moist and can promote disease-causing organisms such as salmonella or EHEC. Pay attention to hygiene, clean water and daily rinsing. Risk groups – small children, pregnant women, older and immunocompromised people – should only eat sprouts cooked.

Common mistakes

1. Canning low-acid vegetables, meat or fish in water bath: 100 °C kills no botulism spores – freeze, sour pickle or ferment instead
2. Relying on smell, color or taste as proof of safety: botulin toxin is not perceptible
3. Opening and tasting suspect jars (bulging lid or puffed can): if in doubt throw away unopened
4. Storing vacuum-sealed at room temperature: the oxygen-poor environment favors botulism – keep refrigerated or frozen
5. Thoughtlessly refreezing thawed frozen goods: surviving germs become active after thawing
6. Too little salt when fermenting or vegetables above the brine: the protective low pH does not set reliably
7. Never checking supplies and not rotating: without "first in, first out" homemade goods quietly go past date

Sources: FOPH (botulism), BfR, NCHFP/USDA, FONES "Smart advice – emergency supplies", BLV (date information); as of July 2026. Core rule: acidity and cold inhibit Clostridium botulinum but do not kill spores – reliably killed only when pressure canning at about 121 °C.

Frequently asked questions

Official sources

• FOPH Botulism – causes, symptoms, prevention
• BfR Questions and answers on botulism
• FONES Smart advice – emergency supplies
• BLV Food label: date information
• Tox Info Switzerland Poisoning helpline 145 (24 h)
• Guide: Build emergency supplies Weekly supply at home (pillar)
• Guide: MRE & emergency rations Long-lasting emergency food
• Guide: Drinking water treatment Make water safe
• Guide: Survival times without water & food How long the body holds up
• Emergency medicine: Poisoning First aid for poisoning (145)
• Scenario: Power outage Frozen goods during blackout
• Emergency supply calculator How much supply your household needs – calculate