Fermented foods: which ones contain live bacteria

On the chilled shelf, two jars of cabbage look like the same product. One holds millions of live bacteria; the other, none at all. The front of the label does not say so — the small print does, and the difference between them is exactly why anyone buys sauerkraut in the first place.

This article is about that: what a fermented food actually is, what it does to the gut microbiota according to the only controlled trial that measured both things at once, which of the ones we stock reach your plate alive and which do not, and when it is better not to push it. With names, with figures, and saying out loud what we do not know.

In short

• A fermented food is, by consensus definition, a food made through deliberate microbial growth. Not all of them arrive alive: bread and wine are fermented and carry no active microbes.
• Fermented is not a synonym for probiotic. A probiotic is a specific micro-organism with its own evidence of benefit. Almost no commercial fermented food meets that definition.
• In the Stanford trial (Cell, 2021), 36 adults; those who went up to 6 daily servings of fermented foods increased their microbiota diversity and lowered 19 inflammatory proteins, interleukin 6 among them.
• In the other arm of the same study, going from 22 to 45 g of fibre a day moved neither diversity nor inflammation in 10 weeks.
• Pasteurised = no live bacteria. That is the word to look for on the label, and it is why good miso says "unpasteurised" on the jar.
• A gherkin in vinegar is not fermented: it is pickled. Two different things, and both are on our shelves.
• Some people do not tolerate them: fermented foods are the main dietary source of histamine and tyramine.

What a fermented food is and what it does to your microbiota

The reference definition is from 2021: an ISAPP expert panel, published in Nature Reviews Gastroenterology & Hepatology, agreed that fermented foods are "foods made through desired microbial growth and enzymatic conversions of food components". Two important nuances follow. First: the fermentation is deliberate, it is not food gone off. Second: not all of them contain live micro-organisms when you eat them. Bread is fermented and then baked; beer is fermented and then filtered.

The same panel insists that "fermented" and "probiotic" are not interchangeable. A probiotic is a specific, identified strain with its own studies showing a benefit at a given dose. Most commercial fermented foods carry undefined microbial consortia — a mixture nobody has fully characterised — which is why they cannot be called probiotics. That does not make them useless: it makes them something else.

The trial that changed the conversation

In July 2021, Wastyk and colleagues published in Cell a randomised study with 36 healthy adults, 18 per arm, within a 17-week design including 10 weeks of intervention. One group raised fermented food intake from practically zero to six servings a day — yoghurt, kefir, fermented cottage cheese, kimchi and other fermented vegetables, vegetable brine drinks and kombucha. The other raised fibre from 22 to 45 g a day.

The results were asymmetric, which is what makes them interesting. In the fermented group, microbiota diversity rose steadily and blood levels of 19 inflammatory proteins fell, including interleukin 6, which has been linked to rheumatoid arthritis, type 2 diabetes and chronic stress. In the fibre group, diversity stayed stable on average and none of those 19 proteins fell, although the bacterial enzymes that digest fibre did increase.

Read it with a cool head: 36 people, 10 weeks. It does not prove that fermented foods cure anything. What it does show is a consistent signal across two separate measures — gut ecology and inflammation — from a dietary change anyone can make. And it unpicks a comfortable idea: that fibre alone is enough. In that trial, fibre on its own did not move the needle in 10 weeks.

The fermented foods we stock and what each one is for

1. Sauerkraut: cabbage, salt and time

Cabbage fermented by the lactic bacteria already living on the leaf. If it sits in the chilled aisle and has not been through an autoclave, it carries live bacteria. We stock Kramer's fresh sauerkraut, SantaPaciencia's red cabbage version and the Mediterranean one from Enso Ferments. Start with a spoonful, not a plateful: the change in gut gas over the first few days is real.

2. Kimchi and lacto-fermented vegetables

Kimchi adds chilli, garlic and ginger to the cabbage, and comes out of the same lacto-fermentation. There is spicy red kimchi and mild kimchi from Sants Ferments, plus Bionsan's lacto-fermented kimchi. And if heat is not your thing, the lacto-fermented carrot with turmeric does the same job without the burn. All of it lives in precooked and canned.

3. Kefir: the easiest one to slot into a routine

It is the most varied fermented food in the whole catalogue, and the easiest to adopt because you drink it. There is milk kefir — goat from Cantero de Letur, sheep, cow — and water kefir, which contains no dairy: the lemon one from KéfirFoods is the mildest place to start. The milk ones sit in the chilled aisle; the water ones in drinks.

4. Yoghurt: the only one with a sentence the EU allows

Of all fermented foods, yoghurt is the only one with an authorised health claim in the European Union. The official English wording is this: "Live cultures in yoghurt or fermented milk improve lactose digestion of the product in individuals who have difficulty digesting lactose". The condition: at least 10⁸ colony forming units of live starter micro-organisms per gram (Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus). Anything else you read on a yoghurt pot — defences, transit, wellbeing — is not authorised in those terms.

5. Miso and natto: the ones that need "unpasteurised" on the label

Miso is soy fermented with koji over months; natto is soy fermented by Bacillus subtilis, with that sticky thread that makes it unmistakable. Here the key word is printed on the jar: Kensho's genmai miso and Terrasana's mugi miso say "unpasteurised" precisely because that is what sets them apart. Somenoya's natto is in the freezer for the same reason. Practical rule for miso: add it off the heat, at the end; boil it and you destroy what you came for.

6. Tempeh: fermented, and protein too

Soy or chickpea fermented by Rhizopus into a solid block. Vegetalia's soy tempeh gets cooked, so the bacteria do not arrive alive, but fermentation has already done part of the work: it pre-digests proteins and cuts the antinutrients in the pulse. It is in the chilled aisle.

Table 1. Which ones carry live bacteria and which do not

How to read the label in ten seconds

You do not have to trust the front of the pack. Three checks settle it:

1. Look for "pasteurised". If it is there, there are no live bacteria. If it says "unpasteurised", there are. Producers who really ferment tend to boast about it.
2. Look at where the jar was sitting. A live ferment needs cold or freezing; if it was on an ambient shelf with no warning, it was probably heat-stabilised.
3. Read the ingredients. Cabbage, salt and water is sauerkraut. If vinegar shows up on the list, it is a pickle: the acid came out of a bottle, not from bacteria.

Three myths worth dropping

"Anything in vinegar is fermented"

No. Pickling means submerging in acetic acid; fermenting means letting bacteria produce that acid themselves by eating the vegetable's sugars. The result tastes similar and is nothing alike on the inside. Our Alélor cucumber in vinegar is an excellent pickle for a sandwich and delivers no live bacteria. We say so even though we sell it.

"Fermented is the same as probiotic"

Also no. The ISAPP consensus is explicit: the terms are not interchangeable, and most commercial fermented foods do not meet the definition of a probiotic because nobody has demonstrated the benefit of their particular strains at a particular dose. If what you want is a strain studied for a defined problem, that lives in digestive and probiotic enzymes, not in the cabbage jar.

"The more fermented food, the better"

This is the one that works against our own sales. Fermented foods are the main dietary source of biogenic amines, and EFSA reviewed this in 2011: histamine and tyramine are the two that matter for food safety. The thresholds it set speak for themselves. For tyramine: 600 mg in healthy people not taking MAOIs, 50 mg with third-generation MAOIs and 6 mg with classic MAOIs. For histamine in people with intolerance: below the limit of detection, which in practice means almost none.

Translated: if you take MAOIs, if you have been diagnosed with histamine intolerance, or if every time you eat fermented foods you end up with a headache or flushed skin, this is not for you and it is not a matter of getting used to it. And for everyone else, sauerkraut and kimchi carry salt: check the grams per 100 g, especially with high blood pressure.

How to start without ruining your week

Table 2. Four weeks to reach the trial's servings

Two practical warnings: miso goes in off the heat, and sauerkraut comes out of the jar with a clean spoon and goes straight back to the fridge. A dirty spoon ruins a whole jar.

The shopping list

Live ferments: sauerkraut, kimchi and lacto-fermented vegetables, yoghurts and kefirs from the chilled aisle, water kefir, cheeses and the natto in the freezer. Pantry ferments: miso and condiments, apple vinegar and the rest of the vinegars.

To go with them, which is where the other half of the work happens: vegetables, pulses, wholegrain cereals and seeds from the pantry. Fibre is the food of the bacteria you have just sown; without it, sauerkraut is an expensive condiment. If you would rather the vegetables arrived on their own every week, there are the organic baskets.

And if your case calls for a capsule rather than a jar: digestive and probiotic enzymes and digestive system. Discounted items are in offers.

Do you need probiotics in capsules?

It depends what for. If you are coming off antibiotics, have a specific digestive diagnosis or have been recommended a particular strain, the capsule makes sense: it is the only way to take an identified strain at a known dose. If the aim is to "look after your microbiota" in general, the Stanford trial suggests food does the job, and it is a good deal cheaper.

We are a shop that sells probiotic capsules and also jars of sauerkraut, and for most of the people who ask us the answer is the jar. If you come in with the question, tell us what you have for breakfast first.

Where to buy fermented foods in Barcelona and Sant Cugat

Live ferments are fridge products, and that is where a physical shop wins: you can check the date, see whether it says "pasteurised" and take it home without it spending two days in an ambient warehouse. We are at:

• Provença 242, 08008 Barcelona — Eixample, between Balmes and Enric Granados.
• Còrsega 78, 08029 Barcelona — Eixample, near Sants station.
• Antoni Bell 2, 08174 Sant Cugat del Vallès — Volpelleres neighbourhood, next to the station.

Call us on +34 683 118 961 to ask which sauerkraut came in this week, or write to linverd@linverd.com. What a marketplace cannot give you: someone who turns the jar around, shows you where it says "pasteurised" and tells you that one is not what you want.

Frequently asked questions

How many fermented foods should you eat a day?

In the 2021 Cell trial the group that improved reached six servings a day, starting from almost zero. There is no official recommended dose. One or two servings a day is already a real change from what most people eat, and it is far more sustainable than six.

Does jarred sauerkraut contain live bacteria?

Only if it is unpasteurised. Most tinned sauerkraut sold at room temperature is heat-stabilised, and heat kills the bacteria. Look for "unpasteurised" on the label and check whether the jar was refrigerated: those are the two reliable signals.

Is a fermented food the same as a probiotic?

No. Under the 2021 ISAPP consensus, a probiotic is a specific live micro-organism with its own evidence of benefit at a given dose. Fermented foods carry undefined microbial mixtures and almost none meet that definition. Both can be useful, but they are not the same thing.

Can fermented foods disagree with you?

Yes. They are the main dietary source of histamine and tyramine, and in 2011 EFSA set very low thresholds for people on MAOIs — 6 mg of tyramine with the classic ones — or with histamine intolerance. If they give you headaches, flushing or discomfort, do not push through it; get it checked.

Can I drink kefir if I am lactose intolerant?

Water kefir contains no dairy, so no lactose. Milk kefir and yoghurt do contain it, although their live cultures help digest it: that is what the only EU-authorised health claim for yoghurt says, with a minimum of 10⁸ colony forming units per gram.

Should miso be boiled?

Quite the opposite. If the miso is unpasteurised and you boil it, the micro-organisms you came for die. Dissolve it in a little warm broth and add it to the soup with the heat already off.

Where can I buy fresh sauerkraut and kimchi in Barcelona or Sant Cugat?

In our shops at Provença 242 (08008 Barcelona), Còrsega 78 (08029 Barcelona) and Antoni Bell 2 (08174 Sant Cugat del Vallès), in the chilled cabinet, or in the online shop with chilled delivery. Phone +34 683 118 961. We stock sauerkraut from three producers, mild and spicy kimchi, lacto-fermented vegetables, kefirs and unpasteurised miso.

To keep reading

Everything live is in the chilled aisle and the rest in the pantry; you can order online with delivery in Barcelona and Sant Cugat, or drop into any of the three shops. If this article helped, the blog has its natural companion: the gut reset, how much fibre per day you need — which is exactly what the bacteria in this article eat — and which magnesium to take. And if what is failing is sleep or stress, melatonin for sleep and chronic stress. All of it on the health blog.

This article is general information and does not replace advice from a healthcare professional. If you are immunosuppressed, pregnant, taking MAOIs or other antidepressants, histamine intolerant, hypertensive or have a diagnosed digestive condition, consult your doctor or a registered dietitian before introducing fermented foods regularly.