How does sugar concentration affect yeast activity in dough?

• A. Sugar has no effect on yeast activity.
• B. Higher sugar concentration always speeds up fermentation.
• C. Moderate sugar aids fermentation; excessive sugar inhibits by osmotically depressing yeast.
• D. Sugar slows down fermentation regardless of amount.

Answer: (C)

Yeast activity in dough is influenced by sugar concentration through two main factors: providing fuel for metabolism and creating osmotic pressure. Yeast can use small to moderate amounts of sugar efficiently, fueling glycolysis and gas production that leavens the dough. But when sugar is excessive, the surrounding sugary environment pulls water out of the yeast cells via osmosis, dehydrating them and slowing or stopping their metabolism. So, a moderate amount of sugar helps fermentation, while too much sugar inhibits by osmotically depressing the yeast. The other statements miss this balance: sugar does have an effect, high sugar won’t always speed fermentation, and sugar doesn’t slow it down in all cases regardless of amount.