1. Normal fermentation: Some pickled foods (such as pickled cucumbers and pickles) are made by fermentation. In the normal fermentation process, bacteria will convert the sugar in the ingredients into acid and gas. Sometimes, this process will lead to the formation of some white deposits or films on the surface of food. This is usually normal and will not cause problems to food safety. Pickled sauerkraut is usually safe to eat as long as there is no obvious abnormal change in appearance, smell and taste.
2. Poor fermentation: If the fermentation process of pickled sauerkraut is disturbed, it may lead to abnormal fermentation and produce bad bacteria or harmful substances. In this case, pickled sauerkraut may have abnormal smell, taste, color or texture. If you suspect that pickled sauerkraut is not fermented well, you'd better not eat it to avoid food poisoning.
3. Mold: White film may also be a sign of mold. Mold is usually unsafe, so it is not recommended to eat pickled sauerkraut if there is obvious mold on it. Mold usually has a strong smell and color, which is easy to identify.
Most importantly, if you feel uneasy about the state of pickled sauerkraut or doubt whether it is safe, you'd better follow the principle of caution and don't eat it to avoid causing health problems. If you are not sure, it is best to consult a food expert or food safety agency. In addition, proper storage and treatment of pickled Chinese sauerkraut will help to prolong its shelf life and reduce risks.