Dear Mr. Wizard:

I went out to have a drink last Saturday and had a quarrel with one of my friends about the usefulness of foam. I said that the foam helps to retain the cool temperature of the beer, but no one believed me. I felt like an idiot. Can you tell me the usefulness of foam? Please reply as soon as possible, or I will never go out drinking with my friends again.

Eddie Chan
via e-mail

Mr. Wizard replies:

I really like beer foam — in fact, I’m kind of obsessive when it comes to beer foam. Any argument about foam is positive in my book, so you shouldn’t feel like an idiot. In a controlled environment, you could probably demonstrate an insulating effect at the surface of beer. But in the hand of the consumer, the beer will be warmed by the temperature of the drinker’s hand.

The drinking vessel itself has more to do with insulation than foam. Aluminum cans conduct heat very well and are good for rapidly chilling beer as well as rapidly warming it. Heavy glass or clay mugs are good insulators, as is the wonderfully American “cup cozy.”

Beer foam affects the mouthfeel of beer and increases the creamy sensation of beer when consumed. It also has a very appealing appearance on a freshly poured beer. If it leaves a nice lacy pattern on the glass, it’s considered truly superior foam. Most brewers like foam for these reasons; they want to produce a beer that has a nice foam volume with good stability and lacing. To many consumers, however, foam occupies space in their glass that could be filled with beer. This is where the brewer and the beer consumer often run into arguments. I explain to people who drink my beer that the foam is a gift from me. It makes the beer visually appealing and improves the mouthfeel. I like to use beer glasses with a fill line to establish the volume where the beer stops and the foam begins. And the next time I’m in a debate about the usefulness of foam, I’ll add the bit about preventing heat loss from the top of the beer. If nothing else, it makes for a nice story!

Mr. Wizard, BYO's resident expert, is a leading authority in homebrewing whose identity, like the identity of all superheroes, must be kept confidential. To see more of Mr. Wizard, check out the latest issue of Brew Your Own at better homebrew stores and newsstand locations.