This paper examines Georg Ernst Stahl's first book, the Zymotechnia Fundamentalis, in the context of contemporary natural philosophy and the author's career. I argue that the Zymotechnia was a mechanical theory of fermentation written consciously against the influential "fermentational program" of Joan Baptista van Helmont and especially Thomas Willis. Stahl's theory of fermentation introduced his first conception of phlogiston, which was in part a corpuscular transformation of the Paracelsian sulphur principle. Meanwhile some assumptions underlying this theory, such as the composition of matter, the absolute passivity of matter and the "passions" of sulphur, reveal the combined scholastic and mechanistic character of Stahl's natural philosophy. In the conclusion I show that Stahl's theory of fermentation undermined the old fermentational program and paved the way for his dualist vitalism.