why does beer foam stay long in a layer on top of glass, and sodas or other bubbly drinks don’t have this kinda thing?
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The foam/head on a beer is protein, yeast and hops as well as the carbon dioxide gas bubbles.
Sodas only have the latter, and the bubbles dissapear as they pop and the gas is diluted by the air.
When brewing beer you do get some of the protein from the grain, hops and yeast in the beer. It is not much from a nutritional standpoint. But especially the gluten from the grain will form into long chains that can form membranes. This means that the foam gets reinforced by the protein and behave quite differently from other drinks.
Because beer contains a not-insignificant amount of protein which increases surface tension and allows the creation of the foamy head. Other carbonated drinks don’t have the protein so they don’t form the same kind of head.
It’s the same sort of reason why you can whip up egg whites and they get super foamy.
As a related aside, some beers aren’t carbonated they are *nitrogenated.* Since the ability of a gas to escape a liquid and enter the air is regulated by the amount of that gas already in the air, CO2 escapes readily (because there is only a small fraction of CO2 in air). Since the air is around 60% nitrogen it’s much harder for the gas to escape so the bubbles remain in the drink. This gives beers like Guinness their classic creaminess and allows them to stay bubbly, longer.
Foam is just little bubbles that haven’t popped yet. Adding something to the liquid that strengthens the bubbles (like protein, starch, or soap) will let the foam stay longer, often enough to pile on top of each other instead of popping the moment they aren’t surrounded by liquid.
Soda is more or less sugar in carbonated water; neither of those ingredients strengthen the bubbles. Other bubbly drinks might have even less ingredients. However, put some dairy in (like ice cream or milk), and suddenly the bubbles from the soda can last longer than the drink does.
Beer has proteins and starches from the plants used in its brewing, both of which strengthen the bubbles.
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