That’s not beer foam in this picture:
The stuff works very well, and is easy to find… It’s just the juice left in a can of chickpeas. Weird, I know. But the smell disappears and the liquid emulates the thickness and foaminess of egg white pretty exactly.
I read about the substitute here, I’m an article from Tales Of The Cocktail.
The beer cocktail pictured above mixed SouthernTier’s Porter with Averna, Spiced Chocolate Bitters aquafaba foam and more!
The result was sort of like a milkshake with chocolate and coffee notes.