Will brewed coffee kill bread yeast?

Here's why:

* Acidity: Coffee is acidic, with a pH typically around 4.5-5.5. Yeast prefers a more neutral pH (around 5-6). The acidity of coffee inhibits the growth and activity of yeast.

* Caffeine: While caffeine is not the primary killer, it can also have a slight inhibitory effect on yeast growth.

Important Note: The strength of the coffee and the amount of yeast used will influence the outcome. A small amount of weak coffee might not be enough to completely kill all the yeast, but it will likely slow down its activity.

In summary: If you're planning to use coffee in a bread recipe, be aware that it might affect the yeast's performance. You might need to adjust the amount of yeast or adjust the recipe's fermentation time.