Quarter cabbages and remove cores; slice 1/8 in. thick. In an extra-large bowl, combine salt and cabbage. With clean hands, squeeze cabbage until it wilts and releases liquid, about 10 minutes. If desired, add optional ingredients.
Firmly pack cabbage mixture into 4-quart fermenting crock or large glass container, removing as many air bubbles as possible. If cabbage mixture is not covered by 1-2 inches of liquid, make enough brine to cover by 1-2 inches. To make brine, combine 4-1/2 teaspoons canning salt per 1 quart of water in a saucepan; bring to a boil until salt is dissolved. Cool brine before adding to crock.
Place crock weight over cabbage; the weight should be submerged in the brine. Or, place an inverted dinner plate or glass pie plate over cabbage. The plate should be slightly smaller than the container opening, but large enough to cover most of the shredded cabbage mixture. Weigh down the plate with 2 or 3 sealed quart jars filled with water. If using a glass container with a lid, cover the opening loosely so any gas produced by the fermenting cabbage can escape. Alternately, you can cover the opening with a clean, heavy towel. If using a crock, seal according to manufacturer's instructions.
Store crock, undisturbed, at 70°-75° for 3-4 weeks (bubbles will form and aroma will change). Cabbage must be kept submerged below surface of the fermenting liquid throughout fermentation. Check crock 2-3 times each week; skim and remove any scum that may form on top of liquid. Fermentation is complete when bubbling stops. Transfer to individual containers. Cover and store in the refrigerator for up to 3 months.