What am I looking at?
Four things turn up on the surface of a jar. Only one of them means you have to throw anything away.
White film, thin and flat
Kahm yeast. Harmless.
A skin of white paint on the surface, sometimes wrinkled or crazed. It lies flat. No fuzz, no height.
It turns up when something sat above the brine, or the jar got warm, or it has simply been a while. Leave it long enough and things taste a little dull. It will not hurt you.
What to do: skim it off with a clean spoon, press everything back under the liquid, carry on.
This is the single most common reason people throw away perfectly good food.
Fuzzy spots, raised, any colour
Mould. The jar goes out.
Mould has texture. It stands up off the surface, looks furry or powdery, and usually arrives in defined circular patches. Green, black, blue, grey, pink, white and fuzzy. Colour does not matter. Texture does.
What to do: throw the whole jar away. Do not scoop around it. Mould sends threads down through the liquid that you cannot see, and the brine carries what it makes. Wash the jar hot and start again.
This feels wasteful. It is one jar, and you will not make the same mistake twice.
Slimy, stringy, ropey liquid
Something went wrong with the salt.
The brine turns thick and pulls into strings when you stir it, like egg white, usually with a smell that is off rather than sour. Not enough salt, or it got warm early on. Rarely dangerous, never good, and it will not recover.
What to do: bin it, and weigh your salt next time.
It smells wrong
Rot, ammonia, solvent.
This is not a texture question and you do not need a chart. If it smells like something died, it did. Out.
Flat and white, skim it. Fuzzy and raised, bin it. Sour is good, rotten is not.
The first week
A new jar lives on the counter, out of direct sun, at normal room temperature. This is when everything happens.
Open it once a day. Over the sink, lid off, let the gas out, lid back on. It will hiss. That is applause.
Press everything under the liquid. Clean spoon, push down. This is the whole job. Anything sticking up above the brine is where mould starts, and nothing below it can go wrong.
Taste it from day two. Clean spoon, never the one that was in your mouth. It goes salty, then sour-ish, then actually good. You are waiting for a clear, pleasant sourness.
When it tastes right to you, move it to the fridge. Usually somewhere between day two and day seven.
A warm kitchen is faster. In August it might be done in a day. In January it might take four. Taste it, do not count days. The clock on your wall knows nothing about your kitchen.
Put a plate under the jar. Brine escapes. Learn from us.
The long life of a jar
Cold slows fermentation down. It never stops it. Your jar keeps changing for months, and every stage is edible. They are just different foods.
- Week 1 to 3
- Crunchy, bright, gently sour. The raw stage. Straight from the jar, on rice, on toast with butter, alongside anything rich.
- Month 1 to 3
- Properly sour, softer, deeper. Most people's favourite window. Still good raw, and it starts making sense in cooked dishes.
- Month 3 on
- Very sour, very funky, soft. Not a failure, cooking material. Stews, fried rice, pancakes, braises, anything with fat and heat to meet it.
If it is too sour to eat straight, it is not dead. It has become an ingredient.
Keeping it alive in the fridge
- Everything stays under the brine, always. Same rule as week one.
- Clean utensil every time. Never fingers, never a used spoon. Almost every ruined jar was ruined by a spoon.
- Label the jar with the date you made it. You will want to know, and you will not remember.
A note on eating it
Raw ferments are genuinely alive, and a spoonful carries a great deal of bacteria. Cooking kills them, so a stew made with your kimchi is delicious and is not a probiotic. Little and often does more than a big serving once a week.
What we will not tell you is that it will fix anything specific. The research is promising and thin. Everyone in this world overclaims. We would rather you just enjoyed the food.
When it does not go to plan
Gone mushy after a week. Not enough salt, too warm, or left on the counter too long. Into the fridge sooner next time, and weigh the salt.
Too salty. Under-rinsed, if it was a cabbage ferment. It mellows as it sours, so give it time before you judge it.
Nothing is happening. No bubbles, no sourness. Three usual suspects: the kitchen is too cold, the salt was iodized, or the water was chlorinated. Move it somewhere warmer and check the salt packet.
The brine does not cover the vegetables. You did not pack it hard enough. Press down with a fist. If it still will not cover, top it up with a 2% salt solution, which is 20g of salt per litre of water.
It tastes of nothing. Under-fermented, or the seasoning was too polite to begin with. Give it more time on the counter, and be bolder next time.
The salt rule, if you only keep one number. Weigh your vegetables, use 2% of that weight in salt. Everything else is preference.
Properly salted vegetables kept under their brine almost never become dangerous. They go bad in ways you can see and smell long before they could ever hurt you. That is the whole reason humans have been doing this for thousands of years without refrigeration or a thermometer. You are allowed to trust it.