1. Reason: Yogurt acidity is probably related to temperature. It may be that the machine has not reached the constant temperature of 40 to 45, and the most likely problem is the strain command. If it can reach a constant temperature, there is no problem with the strain. Five hours is enough, and the longer the fermentation time, the more sour it will be.

2. The original yogurt must be selected as the strain, and the production date should not be too long, because the longer the time, the higher the storage temperature, and the less the probiotics in the yogurt.

3. Boil the small pot and glass bottle, disinfect and dry. Mix whole milk and yogurt evenly, then add milk powder and whipped cream, and finally pour in the remaining milk. The mixture was sieved once and fermented in a yogurt machine for about 8 hours. Then let it cool and eat it directly.