Hello there. This is a very common issue that many home fermenters encounter at some point, so please do not be discouraged.
The thick, slimy, or stringy texture in your brine is typically caused by specific strains of lactic acid bacteria, most notably Leuconostoc mesenteroides. During the early stages of fermentation, these bacteria can produce complex carbohydrates called dextrans or exopolysaccharides, creating a condition often called ropiness. This phenomenon usually occurs when the ambient fermentation temperature is slightly too warm (generally above 70 to 75 degrees Fahrenheit) or if the salt concentration was slightly lower than the recommended 2 to 2.5 percent.
In terms of safety, the reassuring news is that the bacteria responsible for this slime are standard lactic acid bacteria and are not harmful pathogens. As long as your sauerkraut smells pleasantly tart, shows no signs of mold, and has reached an appropriate acidic state, it is safe to eat.
In many cases, the best course of action is simply to give it more time. As fermentation progresses, other lactic acid bacteria, such as Lactobacillus plantarum, take over and naturally break down these slimy compounds, often clearing the brine on their own within a week or two.
If the slime persists after fermentation is complete, the cabbage remains safe to consume, though the mouthfeel might not be ideal. You can rinse the kraut before eating or use it in cooked dishes like soups and braises, where heat will easily break down the texture. As always with home fermenting, if it ever smells foul or develops strange surface molds, it is best to discard it out of caution.
