It is also possible to bring raw water or dirt when drinking.
When wine is fermented normally, bubbles will come up from below, so there will be some bubbles on the liquid surface, and there will be some wine flavor and fruit fragrance. This situation generally appears after the second day of wine fermentation, which is a normal phenomenon. However, if the foam is not obvious three days before fermentation, it will be accompanied by pungent acidity. That is fermentation failure. Pour it out The key to judging is not whether there is a bubble, but what you can smell when there is a bubble.