If it's a thin surface layer (scum) on the top then it's likely yeast not mold and can be skimmed off. If it's mold it's probably more fuzzy and like lily pads floating in the brine.

In either case, if it's on the surface only and the kraut hasn't turned pink or gray or become slimy, mushy, and/or bad-smelling, then in all likelihood the kraut is still fine.

Your call.

It's critical to make sure you maintain adequate brine strength (enough salt) and keep out the oxygen these organisms feed on. Skim frequently if you see scum and if you have a recurring problem with mold it does no harm to add a bit of vinegar to increase acidity until the lactic acid is sufficient on its own.

Stirring occasionally is also a good idea as it submerges any stray yeast into the brine and deprives the spores of oxygen.

Carol

Thanks Carol! It's not a fuzzy growth, so when you mentioned yeast I realized that's what it is. It even had a yeasty smell. I added a little vinegar to the jars and stirred them. I think they will be fine.

I got my recipe from internet.
It called for just adding salt to it until it has enough water(leached from cabbage) to cover the cabbage ....NO BRINE or water added.
It It is fine. I refrigerated after about 10 days, didn't seed any yeast or mold on it.

The brine forms naturally from the cabbage juices and salt (2.25-2.5% salt by weight).

Carol