Baking yeast is made of single celled microorganisms that need to be alive (u0022activeu0022) to work in bread recipes. u003cbr/u003eThe act of u0022proofingu0022 the dough can tell you whether or not your yeast is active. u003cbr/u003eIn this sticky bun recipe, you will proof the dough by dissolving it in warm milk with sugar. After 5 minutes, the mixture should become bubbly and foamy as the live yeast releases carbon dioxide bubbles.u003cbr/u003eIf there's no hint of foaminess in your yeast mixture after 10 minutes, your yeast is probably dead. Grab a fresh packet and try again!