If mixture does not foam, start over with new yeast. (bakinandeggs.com)
Verstrepen's team is continuing research to breed new yeast strains with characteristics useful to industry, and will soon be adding a brewery to the lab to conduct further experiments. (sciencedaily.com)
Sprinkle yeast over and let stand until yeast is beginning to foam and smells bready (if it doesn't foam after 10 minutes, get new yeast). (bonappetit.com)