Active Dry Yeast

Active dry yeast is baker's yeast, Saccharomyces cerevisiae, dried into small granules that keep for months before use. The cells are alive but dormant, and they wake up when they absorb lukewarm water, then feed on sugars and release carbon dioxide gas that makes dough rise. A 7 g (0.25 oz) packet holds about 2¼ teaspoons, according to Red Star Yeast. It differs from instant yeast mainly in its coarser granules, and from fresh yeast in being dry and shelf-stable.

Dissolve it if your recipe says to, because the traditional method softens the protective outer layer of the granules and shows you the yeast is alive. Mix it into lukewarm water of about 110°F (43°C) and wait roughly 5 to 10 minutes for foam. Some modern bakers, including King Arthur, note that today's active dry yeast can be mixed straight into the dry ingredients. The recipe's water amount and timing were planned around one method, so following it is the safest choice.

Use water at about 110°F (43°C) to dissolve active dry yeast. Red Star Yeast gives 110 to 115°F (43 to 46°C), and America's Test Kitchen kept its test water at or below 110°F. That feels pleasantly warm on the inside of your wrist but never hot. Water above 120°F (49°C) risks harming the yeast, and around 130 to 140°F (54 to 60°C) yeast dies quickly. Cooler water only slows the yeast, so if you are unsure, go slightly cooler.

The most common cause of dough that will not rise is yeast that is old or dead, followed by water that was too hot, a cold room, or too much salt. Test the yeast in lukewarm water of about 110°F (43°C) with a pinch of sugar and look for foam within 5 to 10 minutes. Then check that the water was not above 120°F (49°C), move the dough somewhere gently warm, and confirm the salt was measured correctly. Work through the causes in that order.

There is no single time, but a first rise at normal room temperature often takes around one to two hours, and rich or cold doughs take longer. Judge readiness by the dough rather than the clock: it should look puffy with visible bubbles, grow noticeably in volume, often about double, and feel light and airy. Warmth, the amount of yeast, and ingredients such as sugar and fat all change the pace. A refrigerated rise can take many hours or overnight.

Yes, dough can rise in the refrigerator, and many bakers use an overnight chilled rise. Cold slows the yeast sharply but does not kill it, while flavor compounds keep developing, so the bread often tastes better. Expect many hours rather than the one to two hours of a room-temperature rise. Cover the dough well so it does not dry out, and follow your recipe on whether to bake straight from the fridge or let the dough warm up first.

Keep opened active dry yeast in an airtight container in the refrigerator or freezer, and use it within about 4 months. Red Star Yeast says opened jars must go in the refrigerator or freezer, with the freezer preferred, and be used within 4 months of opening. Unopened jars keep at room temperature away from heat. Write the opening date on the container, and open it briefly to limit moisture and condensation. If you are unsure, test the yeast in lukewarm water with a pinch of sugar.

Yes, yeast gradually loses strength, and the best-by date on the package is the producer's guide to how long it should stay at full strength. Red Star Yeast gives that date as 2 years from packaging for its dry yeast, and recommends using opened jars within 4 months. Yeast kept cool and dry may still work somewhat past the date, while heat and humidity weaken it sooner. Test older yeast in lukewarm water with a pinch of sugar and replace it if it barely foams.