Fermentation Salt Calculator

The Fermentation Salt Calculator turns the weight of your vegetables into the one number that decides whether a jar becomes sauerkraut or compost: how much salt. Pick the vegetable, say whether you are dry salting it or covering it with brine, and it returns the salt in grams, in ounces, and in spoons of the particular salt sitting in your cupboard. More importantly, it reports the salinity your jar will actually settle at — which is almost never the percentage the recipe told you to use.

Why the Vegetable's Own Water Changes Everything

Salt does not care which side of a cell wall it started on. Put a vegetable in brine and osmosis goes to work immediately: water flows out of the cells into the salty liquid, and salt moves in the other direction. After a day or two, the liquid in the jar and the liquid inside the vegetable are at the same concentration. That shared concentration is the real fermentation environment, and it is set by the total salt divided by the total water — the water you poured in plus the water that came in with the vegetable.

The consequence runs in both directions, which is why the calculator always shows you both figures:

• Poured brines get weaker. The vegetable brings water with it, so a jar always ends up below the strength you mixed. The tighter you pack the jar, the bigger the drop.
• Dry salting gets slightly stronger. Salting cabbage at 2% of its weight puts that salt into only the cabbage's own water, which is 92% of the weight rather than 100%. The brine it makes lands near 2.2%.

The Math Behind It

Write \( S \) for the salt, \( W \) for the water you pour in, \( V \) for the vegetable weight and \( w \) for the fraction of the vegetable that is water. All the salt ends up dissolved in all the water, so the salinity the jar settles at is:

$$\text{finished salinity} = \frac{S}{S + W + V \times w}$$

That is the equation every other salt calculator leaves out, because it needs to know what vegetable you are fermenting. Turn it around and you can ask for the strength you actually want instead of guessing at a recipe percentage. For a target \( p \) expressed out of 100:

$$S = (W + V \times w) \times \frac{p}{100 - p}$$

That inversion is what the of the finished jar option does. Set it to 3.5 and you get a jar that measures 3.5, not a jar that started at 3.5 and drifted down to 1.8.

The Two Methods

Dry salting — the vegetable makes its own brine

Used for sauerkraut, kimchi, curtido and chilli mash. You shred or chop the vegetable, weigh it, add a percentage of that weight in salt, and work it with your hands until it goes wet and limp. The salt draws out enough juice to submerge the vegetable in its own liquid. Nothing is poured in, so the maths is simple — but whether it makes enough juice depends on how finely it is cut and how hard you work it, which is what the brine forecast in the results is for.

Poured brine — the vegetable sits in salt water

Used for cucumbers, beans, carrots, cauliflower and anything you want to keep whole and crunchy. Firm, low-surface-area vegetables never release enough liquid to cover themselves, so you make brine separately and pour it over. Here the dilution effect is at its strongest, and the vegetable-to-water ratio in your jar matters as much as the percentage you mixed.

Salt Strength Bands

These are graded on the finished salinity, not on the recipe percentage.

Water Content of Common Fermenting Vegetables

This is the number that decides how much a vegetable dilutes your brine. Garlic barely touches it; cucumber and celery cut it in half.

Why Temperature Changes the Right Percentage

Salt and temperature are two hands on the same lever. Warmth speeds every organism in the jar up, including the ones you do not want, so a hot kitchen needs more salt to keep the lactic acid bacteria in front. A cool cellar does the restraining for you and lets you ferment leaner and tastier.

As a rule of thumb, every 8 °C of extra warmth roughly halves the time to a sour ferment. The calculator slides the recommended percentage up by about 0.045 points for every degree above 20 °C and down by 0.03 points for every degree below, staying inside the range that suits your vegetable. If you want the timing modelled properly rather than as the rough guide shown here, use the fermentation time calculator instead.

Salt Brands Are Not Interchangeable by Volume

This is the most common practical cause of a failed ferment, and it has nothing to do with the arithmetic. A tablespoon holds about 18 g of fine table salt, 14.3 g of Morton kosher salt and only 8.5 g of Diamond Crystal kosher salt. Follow a table-salt recipe with Diamond Crystal and you deliver less than half the salt you meant to — straight into the danger band.

Any pure salt works for fermenting. Avoid iodised salt, which can darken a ferment and slow the bacteria, and avoid anything with anti-caking agents, which clouds the brine. Coarse crystals are fine but dissolve them in a little warm water first. Moist grey and Celtic salts carry roughly a tenth of their weight as trapped brine, so weigh out about 11% more of them.

How to Use This Calculator

1. Choose the method. Dry salting for sauerkraut and kimchi, a poured brine for pickles, or Fill a jar to work backwards from the jar size you own.
2. Pick the vegetable and weigh it. The vegetable sets the water content and the sensible salt range. Weigh it trimmed and cut, exactly as it goes into the jar.
3. Set the salinity you want. Leave it on Recommended for a percentage matched to the vegetable and your room temperature, or switch to I'll set it and choose your own basis.
4. Press Calculate Salt. You get the grams, the ounces, the spoons of your own brand, and the salinity the jar will settle at.
5. Check the jar diagram. Confirm the vegetables stay under the liquid, and follow the top-up recipe if the calculator says you will be short.

Practical Tips

• Weigh, do not spoon. A cheap digital scale removes the single largest source of error in the whole process.
• Keep everything submerged. Mould grows on what pokes out, never on what is under the brine. Use a glass weight, a small water-filled bag, or a cabbage leaf tucked over the top.
• Top up with brine, never plain water. Plain water dilutes the jar exactly where it is already weakest. Mix the top-up at the strength the calculator gives you.
• Use filtered or dechlorinated water. Chlorine is designed to kill the bacteria you are trying to encourage. Leaving tap water to stand overnight is usually enough.
• Add tannins for crunch. A grape, oak, horseradish or blackcurrant leaf, or a pinch of black tea, slows the enzymes that soften pickles. Trim the blossom end off cucumbers for the same reason.
• Label the jar. Write the vegetable, the percentage and the date. It is what turns a lucky batch into a recipe you can repeat.

Troubleshooting

• White film on the surface — usually kahm yeast. Harmless but musty. Skim it, and next time salt a little higher and keep the jar cooler.
• Fuzzy or coloured mould — discard the batch. It means something was above the brine, or the salinity was too low.
• Soft or mushy — too little salt, too warm, or the blossom end left on the cucumbers. Raise the salt and ferment cooler.
• Nothing seems to be happening — too much salt or too cold. Below about 12 °C a ferment can take a month to show bubbles.
• Too salty to eat — soak it in fresh water for an hour before serving, and drop the percentage next time.

Frequently Asked Questions

How much salt do I need per kg of vegetables?

For dry-salted ferments such as sauerkraut and kimchi the standard is 2% of the vegetable weight, which is 20 g of salt per kilogram of cabbage. For vegetables submerged in a poured brine you need considerably more, because the water you add has to be salted too. A kilogram of cucumbers packed into a jar with roughly 700 ml of water needs about 55 g of salt to reach a true 3.5%, not the 24 g a percentage of the water alone would suggest.

Why does my pickle brine end up weaker than the recipe says?

Because vegetables are mostly water. A cucumber is about 95% water by weight, and once it has been sitting in brine for a day that water has joined the brine and diluted it. If you mix a 3.5% brine and then pack the jar half full of cucumbers, the finished salinity settles near 1.8%, which is low enough for mould and soft spots. This calculator counts the water inside the vegetables so the number it gives you is the one the jar actually ends up at.

Is 2 percent salt enough for sauerkraut?

Yes. Two percent of the cabbage weight is the long-standing standard and it lands near 2.1% in the brine the cabbage releases, because cabbage is about 92% water rather than 100%. That is comfortably inside the safe range. Go towards 2.5% in a warm kitchen or for a ferment you intend to keep for months, and no lower than about 1.5% in any case.

What kind of salt should I use for fermenting?

Any pure salt without additives works. Pickling salt, fine sea salt and plain table salt are all fine. Avoid iodised salt, which can darken a ferment and slow the bacteria, and avoid salt with anti-caking agents, which makes the brine cloudy. What matters far more is weighing rather than spooning: a tablespoon holds about 18 g of fine table salt but only 8.5 g of Diamond Crystal kosher salt, so a volume measure can deliver less than half the salt you intended.

Do I need to add water to sauerkraut?

Usually not at first. Salted and pounded cabbage releases roughly 150 to 250 ml of its own juice per kilogram over the first day, which is normally enough to cover it once it is packed down tightly. If it is still not submerged after 24 hours, top up with brine mixed at the same strength as the ferment rather than plain water, so you do not dilute it. The calculator tells you how much extra liquid to expect and how much salt to put in the top-up.

What happens if I use too much or too little salt?

Too little, below about 1.2%, and there is not enough salt to hold back mould, yeasts and spoilage bacteria while the lactic acid bacteria establish themselves, so the ferment goes soft, slimy or mouldy. Too much, above about 5%, and the lactic acid bacteria themselves are slowed down, so the ferment barely sours and stays salty. Between roughly 1.8 and 3.5% covers almost every vegetable ferment.

Additional Resources

• Fermentation in Food Processing - Wikipedia
• Sauerkraut - Wikipedia
• Lactic Acid Fermentation - Wikipedia
• Osmosis - Wikipedia