Sauerkraut/sourkraut - ratio of grams of salt to grams of raw cabbage?
2% (20g per 1000g) would be my default recommendation based on sources local to me, but with care less salt may work if sanitation is extremely good (to minimize introduction of undesirable bacteria which the salt helps to supress.)

On the high end, I can say that 4% seems to slow things down, but work, and 8% seems to be simply too much. The pictured jars are 2%, 4% and 8% salt, using red cabbage, which acts as a pH indicator. The 8% jar (rightmost) has not turned pink (and is growing mold on the surface) while the other two are successfully acidifying (the 2% somewhat faster than the 4%) and mold-free. The lids are put on "fingertip-tight" as in canning, so they form a crude but effective airlock seal (they "burp" themselves as needed, just as in canning - they are not loosened manually to relieve pressure.)





Actually 75% red cabbage and 25% apples for these. And the stuff on top is some ceramic tile as improvised weights. Other than for pictures, they are kept in the dark.