мн. уст. yeast sg.
пивные ~ brewerś yeast, barm
Большой русско-английский словарь
ДРОЖЖИ
только мн. yeast, barm, leaven ед. пивные дрожжи – barm, brewer's yeast ставить на дрожжах – to make with yeast, to leaven тесто на дрожжах – yeast dough, baker's dough как на дрожжах – (to grow) by leaps and bounds