In addition to taking her two younger sisters out for fun, Lin Yuan also had some important business in town. The ten pounds of beans she had purchased were already soaked, and all that was left was to grind them into soy milk and then coagulate them into tofu. To do this, gypsum was needed, but since she didn't have it, she could only use the most traditional method to make a batch, and then collect the gypsum later. Therefore, white vinegar became essential.