Kimchi needs about five to seven days in the fridge to ferment into something you would recognise as kimchi, and then it carries on souring slowly for weeks afterwards. That is the whole answer, and it is also why no single number is really correct: kimchi is not a dish that finishes, it is a dish that keeps moving, mild and crunchy in week one and pleasingly punchy by week three.
What follows is what happens during those days, how the taste changes as they pass, how to tell whether your jar has stalled, and how to steer it towards the sourness you actually want.
How long does kimchi take to ferment?
From a standing start, plan for about a week. The hands-on part takes an afternoon: roughly an hour and a half of brining the cabbage, plus making the porridge and the chilli paste and mixing everything together. After that the kimchi goes into the fermentation bag with the air squeezed out and into the fridge for five to seven days.
Taste it every few days as it goes. That is not just quality control, it is the only way to learn where your own preference sits, and it is the reason our Kimchi Making Kit makes two big batches rather than one. The first batch teaches you what you like, the second one delivers it.
What is actually happening during those days?
Lactobacillus bacteria, which are already living on the cabbage, convert the natural sugars in the vegetables into lactic acid. That acid is doing two jobs at once: preserving the kimchi, and creating the distinctive tangy, sour flavour that grows stronger the longer fermentation runs.
Two side effects tell you it is working. The first is gas. If the fermentation bag starts puffing up, that is completely normal, and the fix is simply to check the bag daily and release the pressure whenever it builds. The second is the smell, which is a proper pong and absolutely nothing to worry about. A silent, odourless bag is the one that would concern us.
Squeezing the air out matters for the same reason. The bacteria doing the good work thrive without air, and less air in the bag also means less risk of anything unwanted growing, so press the cabbage right down and squeeze out as much air as you can whenever you close it.
What does kimchi taste like at each stage?
Here is the arc, in rough terms. Fermentation speed depends on temperature, salt and the cabbage itself, so treat these as landmarks rather than a timetable.
- Days one and two: fresh kimchi. Barely fermented, crunchy, salty and chilli-forward, tasting more like a spicy salad than a ferment. Korean cooks eat it happily at this stage and call it fresh kimchi. Lovely alongside rice, but it has no depth yet.
- Days three and four: the turn. The first proper tang arrives and the raw edge of the garlic and onion softens. The flavours stop being separate ingredients and start being one thing.
- Days five to seven: ready. Clearly sour, still crunchy, complex and savoury. This is where our recipe calls it done and where most people are happiest eating it straight from the bag.
- Week two: settled. Sourness deepens, texture softens a little, and the kimchi becomes noticeably more savoury. Excellent in cooking as well as on the side.
- Week three: punchy. Properly sour, softer, and at its very best fried, stewed or stirred into rice, where its acidity does something no fresh ingredient can.
Finished kimchi keeps around two to three weeks in the fridge once fermentation is done. It carries on slowly souring across that time, which is a feature rather than a fault: a jar that has gone too sour to eat raw is a jar that is about to make an outstanding fried rice.
Why is my kimchi not fermenting?
Nine times out of ten, the answer is patience. If it does not taste tangy yet, leave it a few more days, because the flavour keeps developing across the whole five to seven day window and speed varies from batch to batch.
Three things move that speed. Temperature is the biggest: a cold fridge ferments slowly and deliberately, which is exactly what our recipe intends, but it does mean nothing dramatic happens overnight. Salt is next, since it holds the process in check as well as seasoning the cabbage, which is why the brining stage follows measured quantities rather than a generous hand. And the cabbage itself plays a part, as every head is slightly different.
One earlier stage is worth checking too. If your cabbage never softened properly in the brine, give it longer next time. The hour and a half is a guide, and some cabbages want more, so keep mixing every half hour and wait until it is properly softened before rinsing.
Can you ferment kimchi faster?
Warmth speeds fermentation up, which is why traditional recipes often start a batch at room temperature before it goes cold. Our method keeps the kimchi in the fridge throughout, and we would stick with it, because a slow, cold ferment is the most predictable and the easiest to taste your way through. It is also considerably harder to overshoot.
If you want a punchier result, the reliable route is not more heat but more time. Leave the bag in the fridge for longer and taste every few days until it is where you want it. If you want a milder one, eat it earlier, or use less of the dried red pepper in the paste next time, which changes the heat without changing the ferment.
Whichever way you go, the ingredients that make it work are the specialist ones: sweet rice flour for the porridge that binds the paste, dried seaweed powder, and Korean dried red pepper, plus gloves and the fermentation bag itself. You bring a Chinese leaf cabbage, salt, sugar, garlic, ginger, onion and spring onions. The kit is vegan, gluten free and lactose free, and like everything we make, the kimchi kit is hand-packed in Britain.
Kimchi fermentation FAQs
How do you know when kimchi is ready?
Taste it. When it is clearly tangy and sour rather than simply salty and spicy, it is ready, and that is usually five to seven days in the fridge. Bubbling and a strong smell are both good signs along the way.
Can you ferment kimchi for too long?
Not really, though it does get very sour. Older kimchi softens and sharpens, which makes it less appealing as a fresh side dish and considerably better in fried rice, stews and pancakes.
Why is my fermentation bag puffing up?
That is the fermentation producing gas, and it is exactly what should happen. Check the bag daily and release the pressure whenever it builds up.
Does kimchi have to ferment in the fridge?
Ours does, which keeps the pace slow and predictable and makes it easy to taste your way to the flavour you want. Follow the booklet rather than improvising with warmth.
How long does finished kimchi keep?
Around two to three weeks in the fridge once fermentation is done, souring gently the whole time, so it is mild in week one and punchy by week three.
Ready to start a batch? Take a look at our kimchi making kits.
