Salting and pickling mushrooms without botulism

October, the baskets are full, and jars are standing in kitchens all across Europe. Salted mushrooms, marinades, jars sealed away for the winter, all of it is as much a part of autumn as the forest itself.

And here it is worth saying plainly: of everything that can happen to mushrooms in the kitchen, botulism is the most serious. Not a poisonous mushroom in the basket, not an undercooked mushroom soup, but your own jar, made with love and sealed good and tight.

The basic marinade recipe and the step-by-step rules we have already gathered in how to pickle mushrooms. Here, deeper: why mushrooms in particular are so risky in a jar, what actually protects them, and where the invented numbers online begin.

Why mushrooms in particular are dangerous in a jar

The botulism bacterium is an ordinary inhabitant of the soil. It lies in the ground for years as spores and harms no one, because in the open air it can do nothing. It needs particular conditions, and a jar of preserved mushrooms assembles every one of them at once.

• The mushroom comes in from the soil. It grew right in the leaf litter, and particles of earth cling in the gills, in the pores, in the wrinkles of the stem. Washing a mushroom perfectly clean is next to impossible, and it is with that earth that the spores get into the jar.
• Mushroom flesh is not acidic. On its own it does not create an environment the bacterium cannot survive in. Fruit and tomatoes have their own acid, mushrooms do not.
• A sealed jar has no air in it. And that is exactly what the bacterium was missing out in the forest.
• A pan on your own stove does not sterilise. The spores are far tougher than the bacterium itself, and ordinary boiling in a kitchen does not destroy them. Nor does boiling out the jar.

When these conditions come together, the bacterium wakes up and starts releasing its toxin. It has no smell, no taste and no colour, and the jar can look completely normal while it happens.

That is exactly why the advice to “give it a sniff and taste a little” cannot work here in principle. There is nothing to smell.

What actually makes a preserve safe

The protection rests on three things, and none of them is about an airtight seal.

Acid. In an acidic environment the bacterium does not develop. That is why the vinegar in a marinade is not a seasoning but the main preservative, and cutting it back “so it is not so sharp” means taking the protection away.

Cold. Low temperature holds the bacterium back. Home-preserved mushrooms belong in the fridge or a cold cellar, not on a warm kitchen counter next to the stove.

Access to air. A simple loose plastic lid, used to cover the preserve instead of sealing it, takes away the very condition without which the bacterium does not work.

And here an important word of caution about numbers. A very specific recommendation about the vinegar concentration and the proportions of the brine circulates online, in Ukrainian-language sources above all. We do not repeat it: there is no source behind it, and invented precision in an article about botulism is worse than no number at all.

So the principle is this: take a recipe you trust and do not cut the acid in it. Our basic marinade, with the proportions, is in this article, and working from it is safer than working from a number in the comments under a video.

Why an airtight seal is the riskiest option of all

It sounds strange, because an airtight jar seems like the most reliable thing there is. That is how we were taught: seal it, turn it upside down, wrap it up, and it stands for years.

In fact it is the other way round. The tighter it is closed, the closer you are to ideal conditions for the bacterium: warm, damp, not acidic, no air. Commercially canned food goes through processing that simply cannot be reproduced on a home stove, so a home-sealed jar is not a smaller version of the factory one, it is a different thing.

So the safer path is simple and has been known for a long time: cover it with a loose plastic lid and keep it cold. The preserve will not last as long, but it will not turn dangerous.

And if you really do not want to give up sealed jars, then at least do not stand them in the warm and do not keep them “just in case” for years. A jar forgotten in the pantry for two years is not thrift.

Salting and marinades under a loose-fitting lid

The two oldest methods, and both are safer than a sealed jar, because they do not shut the mushroom away without air.

Salting rests on salt, cold and a weight on top. The classics here are the saffron milk cap and Lactarius resimus (hruzd spravzhnii), and how to handle each of them we set out in the saffron milk cap and Lactarius resimus, the mushrooms for salting. You salt them under a weight, in an open vessel or under a loose-fitting lid, in the cold, not in a sealed jar.

An acid marinade rests on vinegar. Under a loose plastic lid in the fridge it is both delicious and the most predictable of all mushroom preserves. Firm mushrooms do well in a marinade: slippery jack, small honey mushrooms, wood blewit, a firm bare-toothed russula.

The difference between them is that salting relies on salt and cold, and a marinade on acid. An airtight seal helps with neither.

Before the jar: cleanliness and pre-boiling

Half the job is done before the mushrooms ever reach the salt or the vinegar.

1. Take young, whole mushrooms. Old, soggy caps bring more earth with them, and more bacteria.
2. Clean them thoroughly. The gills and the pores, the stem, the wrinkles. This is the very soil this whole article is about.
3. Pre-boil whatever needs pre-boiling. Honey mushrooms, the ground-growing tricholomas, the conditionally edible species, without it they are simply not eaten. The times for each species are gathered in the cheat sheet how long to boil mushrooms.
4. Pour off the cooking water if it is meant to be poured off. Exactly when, we work through in should you pour off the water after boiling mushrooms.
5. Work with clean hands and clean equipment. Wash the jars, scald the lids.

The general threshold for mushrooms as a dish is this: at least 15 minutes at a steady 70–80 °C right through the flesh of the mushroom. That same temperature, 70 °C, destroys the eggs of Echinococcus, which a mushroom can bring in from the forest.

But keep the main thing in mind: this is a threshold for a dish, not a guarantee for a jar. It does not take botulism spores away, and the jar itself is protected by acid, salt and cold.

Honey mushrooms are boiled for at least 30 minutes before preserving and the water is poured away. And one more rule that applies to any new preserve: make the first portion a small one, not a full plate for the whole family straight away.

A word on Lactarius resimus and the woolly milk cap. The advice is to boil them for 10 minutes in plenty of water, one part mushrooms to three parts water, pour the water away and rinse the mushrooms in cold. It is worth knowing where that advice comes from: it is from a Finnish leaflet about reducing caesium-137 levels, not about bitterness and not about botulism. It does not take the bitterness away, and it has no effect on the spores at all. Bitterness is removed by soaking, which we write about in the article on salting.

When a jar goes down the drain untasted

There are signs that say “do not eat” outright. If you see even one of them, the jar goes in the bin, not on the table.

• A swollen, bulging or “clicking” lid.
• Bubbles in the liquid, especially if they rise on their own.
• Cloudy brine or marinade, fluffy mould, slime.
• Liquid has leaked out from under the lid, or the lid came off with a sharp sound when you opened it.
• Any unpleasant, sour or stale smell.
• The jar stood in the warm, or you cannot remember when you closed it.

And now the most important part, and it is rarely said. The absence of all these signs does not mean the jar is safe. Botulinum toxin changes neither taste, nor smell, nor appearance, so a normal-looking jar proves nothing.

So the rule is simple, if an unpleasant one: if in doubt, pour it out. No jar of mushrooms is worth the risk, and this is not the moment to feel sorry for the work you put in.

Do not taste it “on the tip of a fork” to check. Do not give a preserve like that to the dog or the cat. And do not count on boiling a suspicious jar through: there is no way at home to be sure that everything heated as it should, and the price of a mistake here is far too high.

If someone feels ill after a home-made preserve, that is no reason to wait until morning. Especially when problems with vision, speech, swallowing or breathing appear: in that case you call an ambulance immediately and say that the person has eaten home-preserved mushrooms.

The myths that get people poisoned

• “Boiling destroys any poison.” No. Boiling takes away neither the toxins of poisonous mushrooms nor the spores in a jar.
• “If the lid has not swollen, everything is fine.” No. The toxin can be there with no outward change at all.
• “Grandma did it this way all her life and nothing ever happened.” Home preserving works like a lottery: the conditions are different every time, and twenty lucky jars promise nothing about the twenty-first.
• “The more salt, the safer.” Salt is part of the protection, but it is not a substitute for cold and acid.
• “You can taste the poison.” No, and this is the most dangerous invention of them all.

Alongside these live the myths about identifying mushrooms in the forest: the silver spoon, the onion in the pan, “animals eat it, so it must be fine”, bright colour, pleasant taste. None of it is true, and it bears on the jar in the same way: only mushrooms you are sure of go into a preserve.

Safer ways to preserve mushrooms

If botulism frightens you, and that is a reasonable thing to feel, there are two ways of keeping mushrooms that do not create an oxygen-free environment at all.

Drying. The safest preserve of all: a dried mushroom gives the bacterium neither moisture nor the conditions it needs. How to do it properly is in how to dry mushrooms.

Freezing. Also no botulism risk, and the flavour keeps better than in any jar. The details are in how to freeze mushrooms for the winter.

For many families the sensible compromise is this: dry and freeze the bulk of the harvest, and salt and pickle only a little, under a loose plastic lid and in the cold, to be eaten within the season rather than stored for years.

How much preserved mushroom you can eat

Even a perfectly made jar is no reason to eat mushrooms every day. Ukraine's Public Health Centre advises no more than 200–250 g of wild mushrooms per adult per week: a mushroom is hard to digest and accumulates whatever is in the soil.

And for children under 12, Ukraine's Public Health Centre advises against wild mushrooms altogether. Home-made salted and pickled mushrooms are no exception here, and if anything they are the least suitable form for a child: in a jar, salt, vinegar and the risk we have just worked through are added to the mushroom itself.

Sources

• Botulism on Wikipedia, the source of the general mechanism: spores from the soil, an oxygen-free environment, low acidity, and a toxin with no smell and no taste.
• Guidance from the Public Health Centre of Ukraine's Ministry of Health on eating wild mushrooms, the source of the 200–250 g per week figure and of the warning about children under 12.
• The leaflet from the Finnish food safety authority (Evira) on reducing caesium-137 levels in forest mushrooms, the source of the advice to boil Lactarius resimus and woolly milk caps for 10 minutes in plenty of water and pour it off.
• Guidance from Germany's Federal Institute for Risk Assessment (BfR) and the German Mycological Society (DGfM) on the heat treatment of wild mushrooms.
• Consumer advice from the German state of Hesse on heating mushrooms to 70 °C.