You are talking with a winemaker about yeast. “I know that yeast can survive under both aerobic and anaerobic conditions,” he says, “but what I don’t understand is why they seem to need so much more sugar under anaerobic conditions. I think they gobble a hundred times as much sugar.” Can you explain to him why yeast might need more sugar under anaerobic conditions than under aerobic conditions? Is his estimation of 100 times as much sugar reasonable?