One consequence of alcohol’s chemical versatility is that it readily penetrates the membranes of living cells, which are made in part of fatlike molecules. When it does so, it disturbs the action of the membrane proteins. A high enough concentration of alcohol will cause such a disturbance that this critical boundary between cell and environment fails, and the cell dies. The yeasts that produce alcohol can tolerate a concentration of about 20%, and most other microbes are killed by much less. When the solution also contains acid or sugar, as in wines, alcohol is an even more effective microbial poison. This is why, unlike beer and wine, distilled spirits and such alcohol-fortified wines as sherry and port don’t spoil after they’re opened.