Fermentation
Brine Calculator

What salt percentage should I use?

Salt percentages for fermentation are simpler than they sound, but they vary by vegetable for reasons that matter. Sauerkraut wants about 2% by cabbage weight because the cabbage releases its own water and the salt has to pull the brine out of it. Cucumbers want closer to 3.5% in a water brine because they sit submerged in already-watery surroundings and need enough salt to control the fermentation while keeping the crunch.

The numbers most home fermenters land on are: 2% sauerkraut, 2.5% kimchi, 3% most water-brined vegetables (garlic, green beans, root veg), 3.5% cucumbers and peppers, 5% olives. Those are the targets the calculator above defaults to. They are not religious figures — half a percent in either direction is rarely the difference between a great batch and a failure — but they are useful anchors.

Fermentation brine vs pickling brine — what is the difference?

Fermentation brine is salt and water. Time, lactobacillus, and the vegetable do the souring. A jar of cucumbers in a 3.5% brine on the counter for two weeks ends up sour because microbes ate the sugars and produced lactic acid. The brine itself never contains any vinegar.

Traditional pickling brine starts the souring chemically by adding vinegar to the salt water. That gives you sour vegetables in a day rather than a fortnight, but at the cost of the live cultures and the slow flavour development you get from real fermentation. Both methods use this calculator for the salt portion. Pickling brine adds vinegar on top — typically a 1:1 vinegar-to-water ratio with the salt percentage shown here.

How to measure salt by weight (and why volume measurements fail)

The single most common reason a fermentation brine tastes wrong is salt-type confusion. Diamond Crystal kosher salt has about half the volume density of fine sea salt. That means a tablespoon of one is roughly half the gram weight of the other. Two recipes from two trustworthy sources can spec "1 tablespoon salt per litre water" and produce two very different brines if the salts differ.

Weighing in grams sidesteps the whole problem. The calculator weighs first and translates back to tablespoons for the salt type you have. If you switch from Diamond Crystal to fine sea mid-recipe, the gram weight is the only number that travels intact. Tablespoon counts do not.

The iodised salt warning — why iodine breaks lacto-fermentation

Iodine is a useful additive in everyday cooking and a problem in a fermenting jar. The lactobacillus that drive sauerkraut, kimchi, and brined pickles are sensitive to iodine and other antimicrobials. A jar with iodised salt will often start cloudy, develop strange off-flavours, or simply refuse to bubble at all.

The fix is to use non-iodised salt. Fine sea salt, pickling salt, and kosher salts are all safe choices. Read the label — table salt often hides iodine and anti-caking agents that interfere even at low doses.

Water brine vs dry brine — sauerkraut works differently from cucumbers

Sauerkraut and other shredded vegetable ferments use a dry brine. You weigh the salt against the cabbage itself — typically 2% — and the salt pulls water out of the cabbage to make the brine in the jar. You do not add water at all. The cabbage produces its own.

Cucumbers, peppers, garlic, and most whole vegetables go into a water brine instead. You mix the salt into water at the right percentage and pour the brine over the packed vegetables. The brine percentage is measured against the water weight, not the vegetable weight. The calculator above switches its math when you switch modes so you do not have to remember which is which.

Why is my sauerkraut mushy, too salty, or growing strange film?

Mushy sauerkraut is almost always too little salt. The cabbage softens before the lactobacillus take over. Push the next batch to 2% by weight and use a fermentation weight so the cabbage stays under the brine.

Too salty is usually salt-type confusion. If you used Diamond Crystal kosher tablespoons in a recipe written for fine sea salt, your gram weight came out roughly double the intended amount. Reweigh on the next batch.

White wrinkly film on top is usually kahm yeast, not mould. It is harmless but a sign of low salt, too much exposed air, or too long a ferment. Skim it off, taste the brine underneath, and tighten the next batch. Coloured, fuzzy growth is actual mould — toss the jar and review whether the vegetables stayed submerged.

Brine cheat sheet by vegetable

Most home fermenters land on the same percentages for the same vegetables because the math is driven by what the vegetable releases and how long it sits in the jar. Sauerkraut wants 2% by weight because cabbage releases plenty of water. Cucumber pickles want 3.5% by water because cucumbers stay rigid and the brine has to fend off softening. Olives want 5% because they ferment for weeks and need stronger salt to stay safe.

Hot sauce mash sits at about 2% by vegetable weight, similar to sauerkraut, because the chillies are macerated and release their own liquid. Garlic confit-style ferments work at about 3% in water. The reference table on the calculator page shows the full set.

How long does brined fermentation take?

Time depends on the vegetable, the salt percentage, and the room temperature. Sauerkraut and kimchi want one to three weeks at room temperature. Cucumber pickles want about a week before they hit the fridge. Olives can take six weeks or longer.

Cooler rooms slow everything down. A 16 °C kitchen drags sauerkraut out to a month. A 24 °C kitchen finishes the same batch in eight or nine days but produces softer vegetables. The calculator gives a temperature band note next to the salt result so you can plan around the kitchen you have, not the kitchen the recipe assumed.