Why Is My Kimchi Not Sour?

Kimchi that refuses to sour is almost always a fermentation problem rather than a recipe problem, and there are only four realistic causes. Working through them in order will usually identify it within a day.

First, check your expectations: in a fridge, kimchi takes one to two weeks to develop noticeable sourness. If it has been three days, nothing is wrong.

1. It is too cold

By far the most common cause. Kimchi put straight into the fridge ferments very slowly.

The fix is to leave it at room temperature for one to two days first, until you see small bubbles and the brine turns slightly cloudy, then refrigerate. That initial warm phase is what establishes the culture; the fridge then slows it to a manageable pace.

2. Too much salt

Salt does not prevent fermentation, but too much of it suppresses the lactic acid bacteria you want. If the kimchi tastes aggressively salty rather than seasoned, this is likely.

It is hard to correct after the fact. Next batch, rinse the salted cabbage more thoroughly before mixing in the paste — most recipes call for rinsing two or three times and people often do it once.

3. Nothing for the bacteria to eat

Lactic acid bacteria ferment sugars. A paste with no fruit, no sugar and no starch gives them very little to work with.

This is what the grated pear, apple or the cooked rice-flour paste (pul) in many recipes is actually for — not just texture and sweetness, but fuel. If you left it out to reduce sugar, that is your answer.

4. It is too airtight, or not airtight enough

Kimchi fermentation is anaerobic, so the kimchi needs to be submerged under brine. Floating cabbage above the liquid line does not ferment properly.

At the same time the container needs somewhere for gas to go, or pressure builds and pushes brine out. Leave headspace, and burp a sealed jar every day or two in the warm phase.