There is something special about the appearance of a creamy head on a homemade stout or the lacing on a glass after finishing a Belgian ale. But beer foam is not just about looks. The bubbles in your beer affect carbonation level, aroma, flavor, and body.
Beer foam is a complex and not fully understood phenomenon. So, what exactly is foam? In simple terms, foam is a dispersion of a relatively large amount of gas in a relatively small amount of liquid. It doesn’t occur spontaneously; it requires some form of energy, either by agitating the beer (e.g., shaking or stirring) or creating a nucleation site (e.g., a scratch on a glass or an engineered device) that allows bubbles to form and rise in the beer, often referred to as “beading.”
So, how can homebrewers improve the foam in their beer?
Choose the Right Malt
Malts high in proteins and dextrin enhance the body and head retention of beer because the proteins act as a structural component in the foam.
The proteins derived from malt are usually hydrophobic (water-repelling), causing them to rise towards the foam where they interact with other foam stabilizing substances, such as those from hops.
However, high levels of proteins and dextrins can interact with tannins, compromise clarity, provide more nutrients for spoilage microorganisms, and result in less fermentable extract per pound of grain (meaning more expenses!). Finding the right balance is the challenge.
There is also a belief that dark malts (e.g., Chocolate) help improve foam stability due to their high levels of Melanoidin, a protein polymer formed when sugars and amino acids combine.
Adjust Your Mash Schedule
Head retention depends on the level of proteins in your wort. Therefore, any step in the mash that breaks down these proteins will negatively affect the foam stability of your beer. For example, the typical protein rest at 120 – 130°F (49° to 54°C) is used to break up proteins that may cause chill haze and improve head retention. However, this rest should only be used when using moderately-modified malts or fully modified malts with over 25% unmalted grain (e.g., flaked barley, wheat, rye, oatmeal) because it breaks down larger proteins into smaller ones and amino acids, reducing foam stability.
In contrast, fully-modified malts (most of what you’ll buy at a homebrew shop) have already utilized these enzymes, and adding a protein rest will reduce body and head retention. To improve head retention, it is preferable to have a full-bodied, higher temperature mash, with a main conversion in the 155 – 160°F (68 – 71°C) range, and avoid intermediate protein rests.
For all you hop enthusiasts out there, here’s more good news—hops contribute to foam stability. As mentioned earlier, the bitter substances from hops, known as isohumulones (a type of alpha acid), help hold the bubbles together. These hydrophobic substances provide a framework for head formation.
However, this interaction doesn’t happen immediately. When you pour a beer, you’ll notice that the foam is wet and loose, but it gradually becomes more solid over a few minutes, adhering to the glass surface, which is called “lacing.”
In other words, the longer you wait to enjoy your beer, the better the foam and lacing on the glass. Overall, highly-hopped beers tend to have better head retention, but it’s essential to maintain a balance between malt and bitterness.
As you may know, some beers are carbonated and poured with a mix of nitrogen and carbon dioxide (CO2). CO2 is relatively soluble in beer and therefore doesn’t promote bubble formation as well as non-soluble gases (e.g., Nitrogen). Nitrogen is less soluble, so it tends to leave the beer and go directly to the foam, reducing gas permeability through the bubbles and causing slower foam coarsening.
However, nitrogen alters the character of the beer, giving it a creamy, thick mouthfeel, and can also reduce the beer’s bitterness. Additionally, the ratio of each gas will depend on the beer style being served, so it’s important to determine the best percentages for a particular style.
The choice of glassware can influence head formation and retention. A tall, narrow glass is a good choice because it minimizes exposure to the surrounding air and reduces the escape of CO2.
Conversely, a glass with a wide opening allows more exposure to air, making it easier for CO2 to escape.
Tips for Better Beer Foam
Ensure proper carbonation.
Choose malts with high protein levels (e.g., crystal malts, dark malts).
Avoid low-protein adjuncts (e.g., corn, rice, sugar).
Wheat malts and flaked barley will increase head retention.
Bittering hops aid in head formation.
Thoroughly sanitize and rinse your equipment.
Adjust mash temperature depending on the grain.
A nitrogen-CO2 gas mix can improve foam stability.
Avoid fats and oils.
Ensure glassware is clean and free of residue.
Measure priming sugar accurately.
Serve beer chilled.
In conclusion, by incorporating various factors that enhance foam, you can achieve a delicious and visually appealing beer.