system
Given the following post, respond as if you're commenting on Reddit:
human
Why is the "head" on soda much shorter lived than on beer?

When soda is poured into a glass, it seems like the foam at the top lasts significantly less time than in most beers. What's behind that?
gpt
Protein! Beer has residual proteins from the grains used to make the beer; these proteins give structural stability to the foam. Most (all?) sodas do not have any protein content to speak of, so there's nothing to stabilize the foam.