Different sources provide different answers to the question of what temperature kills yeast, depending on the medium in which the yeast is used. Here are some key points from the search results:

• In bread, yeast is known to die off entirely once it reaches a temperature of 120 degrees Fahrenheit. Using water thats above 120 degrees in yeasted doughs can negatively affect the structure and flavor of the finished bread by encouraging overproofing or overheating during mixing.
• Yeast in beer will start to die off at around 90 degrees Fahrenheit, which can significantly slow fermentation. As temperatures reach above 100 in beer, most yeast will be dead, and at 120 degrees all the yeast will be dead.
• Yeast in wine can tolerate higher temperatures than yeast in beer, but temperatures above 104 degrees Fahrenheit can kill wine yeast.
• Different strains of yeast have varying tolerance temperature, on both the high side and the low end. As a general rule, 110°F is a safe high temperature.

In summary, the temperature that kills yeast depends on the medium in which the yeast is used. For bread, the temperature should not exceed 120 degrees Fahrenheit, while for beer, the temperature should not exceed 100 degrees Fahrenheit.