In summary the amount of salt or brine strength is a balancing act between stopping the growth of the bad bacteria, encouraging the growth of the beneficial microbes and the flavour.
Too much salt in some fermentations/condiments doesn’t taste great, but sometimes it does because you only use very small amounts!
Low Salt Fermentation
✔ Do not stop bacterial action as effectively as a higher salt level (but faster fermentation (this can be useful when the temperature is very low (in other words below the goldilocks temperature of 21 degrees centigrade))
✔ In normal weather may have greater chance of spoilage because the bad bacterian are not suppressed.
✔ May make the vegetables go soft. Salt preserves the cruchiness of vegetables. Less salt is less preserving of cell wall strength, so ferments can end up with a softer texture especially if the temperature is also high
Higher Salt Fermentation
✔ Lower risk of a failed ferment because the bad bacteria are surpressed (the good bacteria are tolerant of high salt concentrations)
✔ Slows down fermentation which can be useful in warm weather. A slower fermenation may have more complex flavours.
✔ Too much salt can kill off everything including the good bacteria – leading to a failed ferment.
✔ More salt makes veggies crisper because it helps maintain the strength of cell walls, so vegetables in a stronger brine tend to stay more firm and crisp.
So advanced fermenters play around with the amount of salt depending on different factors and what outcome you are looking to achieve – in hot climates for example you may need more salt than in the goldilocks fermenation zone of 21 degrees centigrade to stop the bad bacteria in its tracks.
The sweet spot for most ferments is a 2% – 3% brine solution, with a few vegetables benefiting from stronger brine, up to 5% salinity.
Firmer vegetables like carrots, beets, turnips, onions, garlic, asparagus, and green beans, cabbage can all be fermented successfully with a 2 to 3% brine. That’s 20 to 30 grams of salt for each liter of water.
Softer vegetables like cucumber pickles are very perishable and very full of water (which eventually dilutes the brine), and so need a bit more salt to ferment reliably. While different varieties have different characteristics, thin skinned supermarket/English cucumbers will not work.
A 5% brine, or 50 grams of salt per liter of water, is good for cucumber pickles if you want to keep them in brine for many, many weeks (3% may work if you ferment for a shorter period)
Peppers are more prone to mold than many other vegetables, so they are typically fermented in a slightly stronger brine, too. A 3% to 5% brine usually works well for whole or large-chunk peppers.
Preserving Food Versus Fermenting Food
Very high levels of salt are used to ‘preserve’ rather than ferment food. A very high level of salt kills everything.
Interestingly things like feta cheese for example are preserved for a very long time in a 15-20% salt brine which kills everything good and bad bacteria. Fish sauce also for examplealso doesn’t go off but fish is extremely perishable because it has a salt concentration >10%.