The temperature that kills yeast depends on the type of yeast and the stage of the baking process. In general, yeast will start to die off at around 90°F (32°C) in beer, which can significantly slow fermentation. In bread, yeast is known to die off entirely once it reaches a temperature of 120°F (49°C) . If water temperatures reach above 100°F (38°C) in beer, most yeast will be dead, and at 120°F (49°C), all the yeast will be dead. Regardless of the type of yeast used, if the water temperature reaches 120°F (49°C) or more, the yeast will begin to die off. Once water temperatures reach 140°F (60°C) or higher, that is the point where the yeast will be completely killed off.
Here are some other temperature ranges that are relevant to yeast:
- Water at 68°F to 81°F (20°C to 27°C) are probably the most favorable range for the yeast to grow and multiply in.
- Water at 79°F (26°C) is considered the optimum temperature for achieving yeast multiplication.
- Water at 81°F to 100°F (27°C to 38°C) is the optimum temperature range for the fermentation process.
- Water at 95°F (35°C) is the fermentation temperature for liquids used to dissolve compressed yeasts.
Its important to note that if the water is too cold, then the yeast will simply remain dormant. If yeast is mixed with water at too low a temperature, it can also make doughs sticky and hard to handle.
