Does the yeast in beer weaken when the beer is flat? I use the beer in making bread, and, since I don't drink, it sits in the fridge until I bake bread again. I'm curious whether the yeast weakens in flat beer.


2 Answers 2


By the time you open your beer the yeast has mostly exhausted itself by converting the sugars into alcohol.

You may be able to use it to kick start a sourdough starter, or grow it back to an active bacteria, but it will not be able to leaven a batch of bread by itself from the bottle.


I'm not a bread baker, but I believe that the yeast in beer (what little might be there) is different from yeast used for baking and isn't active in the baking process. However the carbonation in beer might impact the texture or rise of the bread. For this reason flat beer might act differently than freshly opened beer.

  • Baking typically uses slightly different strains, but the same species. Historically a lot of bakeries used to source their yeast from nearby breweries though, so brewers yeast strains can definitely be used for baking.
    – Jack
    Commented May 3, 2021 at 4:24

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