Generally, sour tofu may be due to the addition of brine to the tofu itself, or the fermentation process during production, resulting in some sour taste or smell. If there is brine in the ingredients, or if the tofu is fresh and unopened and still within the shelf life, it is generally still edible. However, if the sour taste is obvious and there is a performance such as becoming sticky, it is generally due to the deterioration of tofu after the shelf life has expired after purchase, or it has been placed for too long, etc. It is not recommended to eat it again. Tofu is rich in protein, so it does not have a long shelf life. When it expires or is placed for a long time, the protein it contains is prone to corruption and deterioration, and it is also susceptible to attack by external corruption bacteria. Although the appearance of some tofu may not change significantly with the naked eye, spoilage cannot be ruled out. After consuming the acidic tofu, the lighter person may have diarrhea, stomach pain and other symptoms, and the serious person may have food poisoning, mainly manifested as nausea, vomiting, loss of appetite, severe diarrhea, and even general chills and other uncomfortable symptoms. Also, some people think that heating the sour tofu can remove the mold, bacteria and other harmful substances in the tofu, but it is actually a misconception that it is difficult to remove these harmful substances even at high temperatures. It is recommended to stop eating it immediately, and if you already have obvious discomfort and cannot relieve it, you should go to the hospital for corresponding examination in time to avoid delaying the treatment. In addition, it is recommended to buy tofu as it is, or boil it in salted water and keep it fresh with water after it cools. Fresh tofu can also be frozen, which gives it a yellowish color and better taste, but it should be thawed naturally before cooking to make it easier to match with other ingredients.