How does food concentration affect yeast activity

Yeast food is sugar and its concentration affect yeast's growth and activity. The process by which yeast metabolize sugar is called fermentation. A sugar concentration that is not very high (up to 3%), increase the fermentation rate. But, with over 3% sugar, the fermentation rate no longer increases. Above 6%, sugar actually decreases the rate because it begins to dehydrate the yeast cells. This effect is called crenation.