If your kimchi does not taste tangy yet, the answer is almost always the same: give it more time. Fermentation speed depends on temperature, on salt and on the cabbage itself, and the flavour keeps developing right across the 5 to 7 days it spends in the fridge, so a batch that tastes flat on day two is usually behaving exactly as it should. This article explains how to tell whether a ferment is genuinely running, what each of those three variables does, and the handful of things that can actually stall a batch.
Worth saying at the outset: a stalled kimchi is rare. An impatient kimchi maker is not.
How do you know if kimchi is fermenting?
You are looking for gas, smell and taste, in roughly that order.
Gas is the clearest sign. If the fermentation bag is puffing up, that is fermentation producing carbon dioxide, and it is completely normal. Check the bag daily and release the pressure whenever it builds. A bag that has inflated overnight is a bag doing its job.
Smell comes next. Fermenting kimchi develops a proper pong, sour and garlicky and unmistakable. That is the sign of a healthy ferment rather than a problem, though it is also a good argument for the bag being well sealed.
Taste is the decider. Open it every few days and try a piece. What you are waiting for is tang, a clean sourness developing behind the chilli and the garlic. Underneath all of this, what is happening is straightforward: Lactobacillus bacteria are converting the natural sugars in the cabbage into lactic acid, and that acid is what preserves the kimchi and gives it its distinctive flavour.
If you have gas and smell but not much sourness yet, nothing is wrong. You are early.
Why does temperature matter so much?
Because the bacteria doing the work slow down as it gets colder, and our Kimchi Making Kit ferments in the fridge on purpose. A fridge ferment is a deliberately gentle one. It takes days rather than hours, and it gives you a longer window in which the kimchi tastes good rather than racing past the point you wanted.
The practical consequences are worth knowing. A fridge running colder than average will simply take longer, and the difference between the back of a very cold fridge and the door can be a day or two of progress. If your kimchi seems slow, the fridge is the first place to look, and nudging the container to a slightly less arctic shelf is often all it takes.
What we would not suggest is trying to speed things up by leaving it out on the worktop. The recipe, the salt level and the timings are built around a fridge ferment, so follow the booklet rather than improvising with the one variable that also governs food safety.
Could it be a salt problem?
Salt is the second lever, and it is the one most likely to have gone astray on a first batch. It does two jobs: it draws water out of the cabbage so the texture stays crisp rather than soggy, and it holds back the organisms you do not want while the lactic acid bacteria get established.
The brining stage is where this is won or lost. Rinse the cabbage, quarter it from the base, cut it into bite-size pieces and soak it in salted water for about an hour and a half, stirring every half hour, then rinse three times. Two things commonly go wrong here:
- The cabbage never softened properly. The 1.5 hours is a guide, not a rule. Some cabbages want longer. Keep stirring every half hour and wait until it has genuinely softened before you rinse, because under-brined cabbage gives you a watery, oddly crunchy kimchi that ferments unevenly.
- It was rinsed too enthusiastically or not enough. Three rinses is the balance the recipe is built on. Wash out too much salt and the ferment loses its guard rails; leave too much and it turns out punishingly salty.
Weigh the salt rather than eyeballing it. Fifty grams sounds like a lot on a spoon and is entirely correct for a whole Chinese leaf cabbage.
What else can slow a batch down?
A few smaller things, all easily fixed.
Air in the bag. The bacteria doing the good work thrive without oxygen, and less air also means less risk of anything unwanted growing. Press the cabbage right down and squeeze out as much air as you can every time you close the bag, not just the first time.
A thin or lumpy porridge. The cooked sweet rice flour is the glue of the recipe, binding the chilli paste and helping it cling to every leaf. Stir it continuously over a medium heat until it is thick, smooth and shiny, roughly the consistency of natural yoghurt, then cool it before the aromatics go in. Sitting the pan in a bowl of cold water is the quick way. If it goes lumpy, keep stirring on the heat and the lumps work themselves out.
Coarsely chopped aromatics. The finer the garlic, ginger and onion are minced, the better the paste, and the more evenly it distributes through the cabbage. A mortar and pestle or a spice grinder is ideal, but a knife and patience get there.
Simple impatience. This is the real culprit far more often than any of the above. The kit makes two big batches, which means you can afford to leave the first one alone and let it teach you what a week actually tastes like.
How sour should it get?
As sour as you like, and it is entirely your call. Kimchi carries on slowly souring after the initial ferment, so it is mild and fresh in week one and pleasingly punchy by week three. Finished kimchi keeps around two to three weeks in the fridge once fermentation is done.
That gradual slide is a feature rather than a countdown. Young kimchi is bright and crunchy and best eaten as a side dish straight from the jar. Older, deeply sour kimchi is what you want for cooking, where the acidity has somewhere to go. If a batch has gone further than you meant, it has not failed, it has simply become a different ingredient.
And if the heat rather than the sourness is the issue, the fix is easy on the next batch: just add less of the dried red pepper to the paste. Since a single kit makes two batches, you get a second run at it with everything you learned the first time.
Kimchi fermentation FAQs
How long should kimchi take to ferment?
Around 5 to 7 days in the fridge, with the flavour developing throughout. Taste it every few days rather than waiting for a fixed date.
Why is my kimchi not sour?
It most likely needs longer. Fermentation speed depends on temperature, salt and the cabbage itself, so leave it a few more days and taste again.
Is it normal for the fermentation bag to puff up?
Yes, entirely. That is gas from the fermentation. Check the bag daily and release the pressure whenever it builds up.
Why does my kimchi smell so strong?
Because it is fermenting properly. A strong, sour, garlicky smell is the sign of a healthy ferment, not a spoiled one.
How long does finished kimchi keep?
Around two to three weeks in the fridge, souring gently as it goes, so it is mild in week one and considerably punchier by week three.
Make two big batches of your own: see our kimchi making kits, hand-packed in Britain.
