You can ferment sauerkraut too long, at which point it will become mushy, and the taste will be too acidic, even though the sauerkraut will still be edible. Longer ferments will intensify the flavors and tangy taste of the sauerkraut. The length of your ferment is usually according to your personal taste. The traditional ferment for sauerkraut is about four weeks, but some people prefer a 3-day ferment.
Yogurt is a cultured dairy product that is supposed to taste sour or tart. A sour taste in yogurt is different from the sour taste in milk when it begins to go off. There are other indicators that will let you know if your yogurt has gone bad or whether it is still good to eat.