What water temperature is best for yeast?

The answer

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.