In this process, once there is enough alcohol and carbon dioxide around in the media the yeast start to die due to the environment becoming toxic to them. There are many strains of yeast and bacteria that can tolerate different amounts of alcohol around in their environment before it becoming toxic, thus one can obtain different alcohol levels in beer and wine, just by selecting a different microbial strain. Most yeast can tolerate between 10 and 15 percent alcohol, but there are some strains that can tolerate up to 21 percent alcohol.