Yogurt machine mainly provides a stable fermentation temperature for fermentation, so if you don't use yogurt machine, you'd better put the milk with strains in a relatively high temperature place (the optimum temperature of lactic acid bacteria is 45 degrees), such as a heat preservation barrel, pay attention to sealing (because lactic acid bacteria are facultative anaerobic bacteria) and extend the fermentation time appropriately. It will taste better with some sugar.