It is! When packaged, baker’s yeast is in an inactive state, effectively asleep but still alive. When you add inactive yeast to flour and room-temperature water, the yeast wakes up and starts doing the two things it does best: eating and farting. The yeast keeps doing this, producing the carbon dioxide that makes baked goods rise, until heated past a certain temperature. Heat kills yeast. So keep your baker’s yeast away from heat until it’s time to use it.