Yeast is a single-cell living organism that feeds on sugar and moisture to grow. It’s a leavening agent in baked goods. Yeast causes the sugar in other ingredients to ferment, creating carbon dioxide. The elastic dough traps the carbon dioxide, which makes the dough rise. Yeast also creates the desired texture and flavor in yeast-based recipes.\nActivating yeast means proving that it's still active and ready to use in baking recipes. Fresh yeast, or cake yeast, is already activated and ready to use without additional preparation. Active dry yeast is a dehydrated version of fresh yeast that doesn't start working until you rehydrate it. Activating, or proofing, active dry yeast is a way to test it to ensure it's still alive and active. When baking bread, proofing the yeast ensures fermentation will happen to make the bread rise properly.\nIt's not always necessary to activate yeast depending on the kinds of yeast used. Before learning how to activate dry yeast, determine the type of yeast the recipe calls for. Don't activate [instant yeast](https://www.masterclass.com/articles/instant-yeast-vs-active-dry-yeast-comparison), rapid rise yeast, or bread machine yeast. They need to stay dry to retain the quick-rise action that speeds up the dough leavening process.\n\nYou don't have to activate dry active yeast, but doing so ensures it's active and will work in your bread. If your dry active yeast is near its expiration date or you opened it more than a few months ago, it may no longer be alive. Activating it before using it protects the dough if the yeast is no longer active.\nTo activate yeast, you need water and a touch of granulated sugar. Follow these steps to activate yeast:\n\n- __Adjust your tap water until it feels lukewarm__. The ideal water temperature to proof yeast is 100–110 degrees Fahrenheit. Hot water above 140 degrees Fahrenheit kills the yeast and won't let the bread dough rise. \n- __Pour water into a small bowl or measuring cup__. Measure ¼–½ cup of warm water, or the amount of water the recipe calls for, in a container.\n- __Add the yeast__. Sprinkle the packet of yeast or the amount of yeast granules that the recipe calls for and a pinch of sugar into the warm water. \n- __Let it sit for five to ten minutes__. If it’s still active, it should turn foamy.\n- __Combine with dry ingredients__. Add the yeast to the dry ingredients as indicated by the recipe. Take note that you might need to subtract the amount of water and sugar added to activate the yeast from the recipe so it doesn’t change the flavor or consistency.\n\nIf the yeast doesn't get foamy or bubbly, either the water is too hot and killed the yeast or the yeast is no longer active. Toss old yeast that doesn't activate and use new yeast for your recipe. The shelf life for unopened dry active yeast is usually about twelve months. It lasts longer if you store it in the refrigerator or freezer after opening it. Once opened, it typically lasts about four months in the refrigerator or six months in the freezer.\nWe’ve got you covered. All you knead (see what we did there?) is The [MasterClass Annual Membership](https://www.masterclass.com), some water, flour, salt, and yeast, and our exclusive lessons from Apollonia Poilâne—Paris’s premiere bread maker and one of the earliest architects of the artisanal bread movement. Roll up your sleeves and get baking. \nMany recipes—such as [pizza dough](https://www.masterclass.com/articles/the-best-homemade-pizza-dough-recipe-plus-12-homemade-pizza-recipe-ideas), cinnamon rolls, dinner rolls, and [bread recipes](https://www.masterclass.com/articles/easy-homemade-bread-recipes)—call for active yeast. Read on to learn how to activate yeast.