Kimchi Explained: Smell, Facts, Gluten & Probiotics

Kimchi is Korea’s national dish — vegetables salted, coated in a spicy paste, and left to ferment until they turn sour, funky, and alive with probiotics. Almost everything people wonder about it, from the smell to the gluten question, traces back to that one process: lacto-fermentation.

What kimchi actually is

Kimchi is most often napa cabbage and Korean radish, salted and then coated in a paste of chilli (gochugaru), garlic, ginger, and fish sauce. Like sauerkraut, it’s a lacto-fermented food: naturally present lactic-acid bacteria convert the vegetables’ sugars into lactic acid. That acid is what gives kimchi its signature sour tang, preserves it for months, and produces the live probiotics it’s famous for.

There are hundreds of regional and seasonal varieties, but the science behind all of them is the same — and it all starts with salt. Cabbage is usually brined at around 2–3% before the paste goes on. Get the ratio right with the salt brine calculator or the fermentation brine calculator so the batch stays crisp and safely sour.

Why kimchi smells the way it does

The smell is the fermentation working. As lactic-acid bacteria consume the cabbage’s sugars they release sour and funky aromatic compounds; the garlic, ginger, and fish sauce add their own sulphurous, savoury notes on top. The result is sour, pungent, and a little funky — sharper the longer and warmer the kimchi ferments. A strong smell is normal and healthy. Here’s how to read what your nose is telling you:

Sour, tangy, a little funky healthy, active lacto-fermentation — exactly what you want.

Sharp and very pungent a mature, well-aged batch; great for cooking, still perfectly good.

Rotten, putrid, or heavily yeasty spoiled — usually alongside fuzzy surface mould. Discard it.

Keeping the vegetables pressed under the brine and the jar cold in the fridge holds the smell in the pleasant-sour range.

Is kimchi gluten-free?

Traditional kimchi is naturally gluten-free. The core ingredients — cabbage, radish, salt, gochugaru, garlic, ginger, and spring onion — contain no gluten. The risk sits entirely in the seasonings:

Fish sauce Most are gluten-free, but some contain wheat-based additives — check the label.

Soy sauce If a recipe uses it, standard soy sauce contains wheat. Use tamari instead.

Thickening paste The porridge that binds the seasoning should be rice or glutinous-rice flour (which, despite the name, is gluten-free) — not a wheat starch.

Malt & barley flavourings These occasionally appear in commercial blends and do contain gluten.

If you’re coeliac or gluten-sensitive, the safest route is homemade kimchi with certified gluten-free fish sauce and a rice-flour paste, or a commercial brand explicitly labelled gluten-free.

How many probiotics are in kimchi?

Raw, unpasteurised kimchi is one of the richest food sources of probiotics. As it ferments, populations of Lactobacillus and related lactic-acid bacteria bloom, with Leuconostoc species early on giving way to Lactobacillus as it matures.

10M–1B+ CFU per gram (raw)

46°C heat that kills the cultures

0 live CFU once pasteurised

Two things quietly kill those probiotics. Heat: cooking kimchi above roughly 46°C / 115°F destroys the live cultures — it still tastes great and keeps its fibre, but the probiotic benefit is gone. Pasteurisation: shelf-stable kimchi sold outside the fridge has usually been heat-treated, so look for chilled, “raw,” or “unpasteurised” on the label if live bacteria are what you’re after.

Quick kimchi facts

Nutritious by nature Low in calories, high in fibre, and a good source of vitamins A and C.

Salty by design Watch the sodium — treat it as a side of a few tablespoons rather than a big serving.

It keeps evolving Kimchi keeps souring in the fridge for weeks and months; older kimchi is prized for cooking.

Vegetarian works too Swap the fish sauce for a seaweed or miso-based umami source. Bubbles and rising liquid are normal, not spoilage.

Make your own kimchi

Kimchi is one of the most rewarding ferments to make at home, and it lives or dies on the salt ratio. Brine the cabbage right, pack it under the paste, and let time do the rest. Loosen the lid daily during the first active week, or fit an airlock — see our guide on burping fermentation jars for the full schedule.

Try the calculator

Fermentation Brine Calculator

Lock in the 2.5% salt kimchi wants for a crisp, safely sour batch.

Open calculator →

Frequently asked questions

Why does kimchi smell so strong?+

Kimchi's smell comes from lacto-fermentation. As lactic-acid bacteria break down the sugars in cabbage they release sour, funky, and sometimes sulphurous aromas — sharpened by the garlic, ginger, fish sauce, and chilli in the paste. A strong, sour, slightly pungent smell is a sign of healthy, active fermentation, not spoilage.

Is kimchi gluten-free?+

Traditional kimchi made from cabbage, radish, salt, garlic, ginger, chilli, and fish sauce is naturally gluten-free. The catch is the seasonings: some commercial fish sauces, soy sauces, and thickeners (like malt or barley-based ingredients) contain gluten. If you're coeliac, check the label or make your own with certified gluten-free fish sauce and a rice-flour paste.

How many probiotics does kimchi have?+

Raw, unpasteurised kimchi is rich in live lactic-acid bacteria — studies have measured anywhere from 10 million to over 1 billion colony-forming units (CFU) per gram, dominated by Lactobacillus and related species. The exact count depends on how long and how warm it was fermented. Pasteurised, shelf-stable kimchi has had most of these bacteria killed off by heat.

Does kimchi go bad?+

Kimchi keeps fermenting slowly in the fridge and gets more sour over months, but it rarely 'goes bad' in the unsafe sense as long as the vegetables stay submerged in brine and you use a clean utensil. Throw it out only if you see fuzzy mould on the surface, or if it smells rotten or yeasty rather than sour and tangy.

Is kimchi good for you?+

Kimchi is low in calories and high in fibre, vitamins A and C, and — when raw — live probiotic bacteria that support gut health. The main thing to watch is sodium: kimchi is salty by design, so treat it as a flavourful side of a few tablespoons rather than a large serving if you're limiting salt.