I am in the process of making babka and need to use yeast. I followed directions, 1/2 cup warm milk, pinch of sugar, 2 1/4 tsp of yeast. I warmed the milk, add a pinch of sugar, added the yeast. It is taking so long for the yeast to get foamy.. I dont know what I did wrong? Directions and video did not say to stir it.. Please advise. Thank you!