If homemade yogurt doesn't set during fermentation, it may be due to insufficient fermentation conditions or other issues. Here are some remedies and suggestions to hopefully help you solve the problem of yogurt not curdling.
If the yogurt does not reach the expected set state, consider continuing fermentation. Keep the yogurt container at the right temperature and let it sit for a while, usually 4 to 8 hours. Sometimes, yogurt takes longer to set completely.
Make sure the yogurt is in a proper fermentation environment. Temperature is a key factor in yogurt fermentation, so try placing your yogurt in a warm place, such as near a water heater or under a heating blanket, to increase the temperature. At the same time, the fermentation time is extended, so that the flora in the pot has enough time to ferment.
If the yogurt doesn't set successfully, try adding new yogurt bacteria to the yogurt that has already risen. You can buy some high-quality live yoghurt or yoghurt powder, mix it with existing yogurt, and then re-ferment it.
If you don't have a suitable warm environment in your home, consider using an insulated device, such as a yogurt maker or thermos flask, to provide a constant and suitable temperature for fermentation.
Sometimes, factors such as the fat content of milk or yogurt, the type of milk, etc., can also affect the coagulation of yogurt. Trying to change a different type or brand of milk, or adjusting the fat content of the milk, can sometimes improve the coagulation of the yogurt.
If none of the above solves the problem, consider using a thickener such as agar, pectin or oatmeal, which can be mixed into the yogurt for reprocessing, which will make the yogurt denser.
When making homemade yogurt, paying attention to hygiene, temperature, and fermentation time are very important factors. In addition, different yogurt production methods will also produce different effects, so you can try a variety of methods to find the right way to make it. If you still don't succeed after many attempts, you can also consult a professional or other experienced yogurt maker for help and advice.