By simmering the moto (the starter mash) in a pot, its volume increased, and undoubtedly simmering must have been performed within a very narrow temperature range because the yeast would have been killed if the temperature was too high.
酛を、釜に入れて煮ることによって酒母造りを行なうのだが、もちろん高熱で酵母が死んでしまわないように、ぎりぎりの温度で留めて行なわれたことに疑いを容れない。