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October 04, 2016

Why Is Beer Foam White?


Have you ever stared at our delicious brews and wondered why beer the foam is white? It’s not an age-old brewer’s secret, but simple science. We didn’t ace this subject in school either, but trust us, it really is pretty easy.


Carbonation is a vital aspect. It can occur naturally through fermentation, as it does in Hofbräu beers, or it can be added to beer. When beer is in a keg its carbonation is stable throughout. When the sealed container is opened the carbonation, which is created by dissolved carbon dioxide gas, loses its equilibrium. The average amount of carbon dioxide gas in the atmosphere is 0.2%, while the average carbonation in beer is 98%. To re-establish equilibrium between the air and the beer, carbonation must leave the beer. This process produces the signature foam found on the surface of beers.


Frothy foam is the key to the signature taste and look of Hofbräu beers. The foam’s color is the product of reflected light and the beer’s color. The bubbles that make up foam are so numerous and small that they reflect and scatter light rather than absorb it. Even though an individual foam bubble is transparent, this reflecting and scattering of light gives the foam a white appearance. Approximately 20% of foam layer is made up of beer trapped between individual bubbles. This captive beer, if light in color, will not affect the appearance of white foam. However, if the trapped beer is a dark beer, then the foam may take on a cream to tan coloration.


What are you waiting for? Come save the trapped beer!