Da-seul, an outstanding student both in personality and academics, is eighteen this year. However, she has an unusual quirk—she loves makgeolli (Korean rice wine) so much that she secretly sips it even at school, carrying it in empty cosmetic bottles. Her family took over a traditional makgeolli brewery when they moved to their current town during her childhood. The brewery is known for sticking to the old-fashioned method of using only yeast, rice, and water, and its flavor is highly praised among the locals. The secret to its taste lies in a mysterious yeast that had been in the brewery since they took over. One day, however, Da-seul undergoes a complete change. The lively, cheerful girl loved by everyone seems to have vanished, and instead, she falls sick, claiming that the yeast has disappeared. Her family insists that the yeast is still there and that it's all just a figment of her imagination, but Da-seul is certain she can feel the absence of the yeast. Determined, she sets out on a quest to find the missing yeast.