Pasteur realized that yeast was responsible for the conversion of glucose to alcohol. By adding yeast to a simple sugar solution, he showed that alcohol could be formed. He also revealed that the metabolism of yeast was pH -dependent; the acid-level played a role in determining wine's properties. One of grapes' two principal acids, tartaric acid (malic acid is the other), led to Pasteur's discovery of enantiomers, molecules that are mirror images of one another.