Foam: Beer’s Crowning Glory

One of the most beautiful things about beer is the product of sound brewing, proper service, and an unlikely convergence of chemical phenomena. But how much do you really know about what makes great foam? Let’s feed your head.

Randy Mosher May 28, 2024 - 12 min read

Foam: Beer’s Crowning Glory Primary Image

Photo: Matt Graves/

Of all alcoholic drinks, beer alone can boast of a dense and lingering mousse topping its liquid depths. Beer’s lively texture and fluffy foam have been admired since ancient times. All the more amazing is the collection of chemical miracles that make that foam happen.

Sure, many drinks have bubbles. In champagne and other sparkling wines, these can be enchanting—glittering, lazily drifting their way up to the surface—and then they simply self-destruct. Wine, wonderful as it can be, lacks the unique mix of components needed for bubbles to form sustainable foam. In cocktails, meanwhile, you must delve into the egg-whites niche—think gin fizz or pisco sour—to find a simulacrum of the impressive head on a well-poured beer.

Carbonation strongly contributes to aroma. Bubbly beverages contain a rich mix of compounds that give off twice as much aroma as still drinks, and this is true for beers as well. It’s also why most wine needs an in-curved glass with a lot of headspace to capture its volatiles.

Beer isn’t so fussy. It’s happily aromatic in a variety of shapes—even the plastic “airline” cups used in competitions. Foam plays a key role in that property, and the mechanisms are as complex as they are fascinating, providing a wide range of possibilities for brewers who want to tinker and for bar staff who want to dial in the most beautiful pint in town.


The Chemistry of Foam

Beer’s long-lasting foam depends upon a very particular mix of components.

The first and most important is a particular type of protein known as lipid transfer proteins (LTP), present in barley and malt. Because much of the biological matrix of life is water-based, it’s challenging for living things to shuttle crucial fatty acids and other water-insoluble compounds through their aqueous environment. With a barrel-shaped cavity enhanced by molecular components that are attractive to fats, LTPs make this possible by encouraging fatty molecules to snuggle inside and safely enjoy the ride to their destination.

An LTP’s cavity is a perfect fit for the waxy hop-bittering compound isohumulone, beer foam’s second essential component. Its presence explains why the foam always tastes much more bitter than the beer itself.

Isohumulone interacts with a third type of component called glycoproteins, which are proteins cross-linked with a carbohydrate. One of the more crucial is the glycosylated form of a barley protein ominously called “protein Z.” Because glycoproteins are produced during malt kilning, amber and dark beers often have better, more persistent foam than pale ones. The isohumulone and glycoproteins are attracted to one another, and they form elastic bonds that help stabilize the foam.


Beer also has a unique body, quite different from wine or any other beverage we know. Its slightly viscous texture results from many things, but especially from a network of interconnected proteins, phenols, and carbohydrates that also help support the persistence of beer’s foam. Called a colloidal state after the Greek word for “glue,” this body builder in beer has the same structure as gelatin, in which participating molecules form a network robust enough to entrap water. It’s a Goldilocks situation: The protein fragments here must be of intermediate length—too small and they can’t form a network; too large and they clump together and fall out as inappropriate haze.

Hops also contribute polyphenols to beer, which can enhance its body as they do in wine. At modest levels—about 200 milligrams per liter—they can also increase the intensity and longevity of bitterness while providing a greater fullness of palate.

Pouring, Serving, and Foam

The method of serving makes a big difference in how a beer’s head presents itself.

In the United States, we have long been relatively indifferent to foam—just a time-consuming nuisance to impatient drinkers. In lager-centric regions of Europe, however, drinkers have learned to be suspicious of a pils that arrives too soon after ordering. Many German drinkers expect it to take three full agonizing minutes to achieve the proper result. If the Czechs pour more rapidly, they do so deftly with their side-pull taps, designed specifically to promote a long-lasting “wet” foam.


Notably, these foam-supporting pours also depend on well-brewed beer, with plenty of available foam components for their fluffiness.

Under carbonated beer obviously presents a challenge, often resulting in a lifeless experience. The exception to this is cask-conditioned ale, which turns gentle carbonation into an asset. British drinkers debate with hammer and tongs the value—and quantity—of foam on their draft beer. Traditionally, there is a preference for foam in the North, where taps may be fitted with restricting “sparkler” devices; pumping the lightly carbonated beer through this sparkler creates a dense, crema-like foam.

Breweries developed “nitro” ales and stouts—Guinness, most famously—to emulate the soft texture of real ale. In beer, nitrogen behaves quite differently from carbon dioxide. Unlike CO2, it barely dissolves. When you release the pressure within a nitrogenated can, the gas rushes out to form the lovely cascade of foam so appealing to Irish-stout drinkers. Despite its insolubility, nitrogen is foam-positive—another reason this trick works.

With packaged beer, an earlier generation of Wisconsin drinkers taught me to pour it “straight down the middle” of the glass. This results in half a glass of foam, so you need to wait, let it settle, and repeat until you have a nice, dense foam on top. This also releases some carbonation, for a creamier and less bloat-inducing pint. Also, rather than popping, many of the bubbles gradually bleed off some of their gas, producing abundant tiny bubbles with robust skins, making for a creamy, long-lasting foam.


In Brazil, the chope (meaning “draft”) is a common form of beer service. Very small (about 10-ounce/296 ml) tapered pilsner glasses are filled with lager, often chilled a bit below freezing, then topped off separately with foam that resembles whipped cream. With the exceedingly light-bodied industrial beers involved, this trick depends on two things: a “creamer” faucet capable of dispensing pure foam, and foam-boosting additives called alginates, derived from marine algae. Otherwise, these beers would not be up to the task. It’s fun to experiment with the creamer faucets; some pour normally when pulled forward but dispense rich foam when pushed backward. Others simply dispense foam for topping.

Fats are the enemy of foam, as many of us who have brewed with fatty ingredients know firsthand. It’s not exactly clear which ingredients, addition points, and methods cause the most trouble, but the usual suspects are nuts, chocolate, coffee, and dairy. It does seem that fats such as butterfat, with a high melting point, are less problematic.

In bar service, grease or lipstick on imperfectly clean glasses is often the culprit. However, detergents also have a fat-friendly side to them, reducing beer’s surface tension and collapsing foam. So, a fat-free but improperly rinsed glass is also a problem.

Bubbles won’t form on a molecularly smooth surface; they require rough nucleation sites. You can often see streams of bubbles emanating from tiny scratches in a glass or—horrors!—from residual crud stuck on its walls. Although it’s not always done, it’s good practice to wipe dry the inside of each washed glass, which will help remove this detritus.


Sometimes, especially for sparkling wines, glasses have bubble-promoting nucleation sites in the bottom. Glassmakers would traditionally etch these using a diamond stylus or, nowadays, laser engraving. In the bottom of Belgium’s iconic Duvel tulip, the etching is in the shape of a “D.” Boston Beer’s Sam Adams lager glass has a small lasered circle; within a few minutes, you can see a perfect donut of foam telegraphed up to the surface.

Brewing for Foam

This important aspect of beer is affected by many factors in both the recipe and the brewing process, which is why good brewers take care to manage them. Certain ingredients and specific processes are considered either foam-positive or foam-negative. Malts are foam-positive, while adjuncts such as rice or corn are not. Hops are foam-positive. Tetra hop, a processed hop product with the “skunkiness” precursor removed, is highly foam-positive and used for that effect. Certain metals may be highly foam-positive but are otherwise not good for beer. Some, such as the cobalt salt that was used briefly in the 1960s as a foam enhancer, are stunningly potent but injurious to health.

How you compose your grain bill and conduct your mash also make a difference. Traditional mashes often included a protein rest—a necessary step with lightly modified malt that has a good portion of high-molecular-weight proteins. With more highly modified modern malts, this rest can degrade the mid-length proteins necessary for body and helpful for head formation.

High heat intensity also can damage a beer’s protein structure. Advanced modern brewing systems are designed to limit heat input to wort, sometimes skipping a proper boil. Gentler means such as sub-boiling temperatures and thin-film evaporation can still achieve pasteurization, protein coagulation, and stripping of DMS and other unwanted volatiles.


Don’t Waste the Foam

One key point about many of beer’s head-forming components is that they may be used only once—after that, they’re useless. Foam that forms in the tank will not form again in the glass.

It’s important to carbonate gradually in the tank. Traditional methods employ a technique called spunding, in which the tank is capped with a pressure-relief valve toward the end of fermentation. This allows natural carbonation to build gradually, thus avoiding in-tank foaming.

Once again, something we all take for granted in beer turns out to be another vast and fascinating rabbit hole of wonder. I, for one, will never look at beer’s foamy finial the same way, and I hope you won’t either.

Further Reading

Want to dig deeper into the science of beer foam? Here are a couple of scientific articles to help feed your fine head:

The Influence of Biomolecule Composition on Colloidal Beer Structure, in Biomolecules, 12 (1), December 2021, by Irina Nikolaevna Gribkova et al.

The Multisensory Perception of Hop Essential Oil: A Review, in the Journal of the Institute of Brewing, 126 (4), September 2020, by Christina Dietz et al.