EnglishViews: 24 Author: Site Editor Publish Time: 2025-05-22 Origin: Site
Beer foam is a complex and far from well understood phenomenon. So, what is foam? In short, foam is a relatively large amount of gas dispersed in a relatively small amount of liquid. It doesn't happen spontaneously - it requires some energy, such as agitating the beer (e.g. shaking or stirring) or creating a nucleation site (e.g. scratching a glass or engineering device) to allow bubbles, sometimes called "bubbles", to form and rise in the beer.
So how can homebrewers improve the foam in their beer?
Malts rich in protein and dextrins enhance the body and head retention of beer, as proteins are the structural components of the head.
Malt-derived proteins are generally hydrophobic (insoluble in water), which causes them to migrate upward into the head where they encounter other effective head-stabilizing substances, such as those from hops.
However, high levels of protein and dextrins can interact with tannins, reduce clarity, provide more nutrients for spoilage microorganisms, and result in less fermentable extract per pound of grain (which means more loss for your wallet!). Finding the right balance is a challenge.
Malts that help enhance foam include crystal malt and wheat malt. It is also believed that dark malts, such as chocolate malt, help improve foam stability because they are rich in melanoidins, a protein polymer formed by the combination of sugars and amino acids.
The persistence of head depends on the amount of protein in the wort. Therefore, any step in the wort curing process that breaks down these proteins will negatively affect the head stability of the beer. For example, a protein rest, typically performed at 49 to 54 degrees Celsius (120 to 130 degrees Fahrenheit), can break down proteins that can cause cold haze and improve head persistence. However, this rest is only appropriate for moderately modified malts, or fully modified malts with more than 25% unmalted grains (e.g., flaked barley, wheat, rye, oats), because it breaks down larger proteins into smaller proteins and amino acids, which can reduce head stability.
In contrast, fully modified malts (most of what you buy at a homebrew shop) already have these enzymes utilized, and adding a protein rest will ruin the body and head persistence of the beer. To improve head persistence, you want to choose a full-bodied, warmer mash with a major conversion temperature in the 155 – 160°F (68 – 71°C) range, and avoid intermediate protein rests.
Here’s more good news for all you hop lovers out there – hops help keep the foam stable. As mentioned above, the bitter substances in hops called isohumulones (an alpha acid) help keep the bubbles cohesive. These hydrophobic substances help form the framework for the foam to form.
However, this interaction doesn't happen overnight. When pouring beer, you'll notice that the foam is wet and thin, but after a few minutes it becomes almost solid, and the foam adheres to the surface of the glass, which is called "lace".
In other words, the longer you drink the beer, the better the beer foam and lace will form on the glass. In general, beers with strong hop flavors should have better foam persistence, but remember to maintain a balance of malt and bitterness.
You may know that some beers are carbonated, with a mixture of nitrogen and carbon dioxide (CO2) poured in. Carbon dioxide is relatively soluble in beer, so it doesn't promote bubble formation as well as insoluble gases such as nitrogen. Nitrogen is less soluble, so it tends to leave the beer and go directly into the foam, reducing the permeability of the gas through the bubbles and slowing the coarsening of the foam.
However, nitrogen can change the characteristics of the beer, making it smoother and thicker, and taking away some of the bitterness of the beer. Also, keep in mind that the ratio of each gas depends on the style of beer you're serving. Be sure to check which ratio works best for a particular style of beer.
The glass you choose can affect the formation and persistence of the foam. A tall, narrow glass is a good choice because it minimizes contact with the surrounding air and reduces the ability of the carbon dioxide to escape.
Conversely, if the glass has a larger opening, there is a greater contact area with the air, allowing the carbon dioxide to escape more easily. For example, many Bavarian wheat beers and pilsners are served in tall, narrow glasses to maintain the formation and persistence of the foam and preserve the overall appearance of the beer.
It may seem obvious, but many beer lovers overlook the importance of glassware. Your glassware should be "as clean as the beer." Follow proper beer glass cleaning procedures and avoid getting greasy stains on it. These take up space on the surface of the beer and prevent bubbles from forming. So, next time you eat a burger or put on lipstick, make sure you wipe it clean!
Other factors
Beer gushing: Sometimes beer starts gushing out as soon as you pop the cap off the bottle. Most experienced homebrewers have experienced this. Next thing you know, your pants and the floor are soaking wet. This phenomenon is usually caused by over-pouring or microbial spoilage. Make sure you carefully measure the amount of pouring sugar and practice good hygiene, and this shouldn't be a problem.
Temperature: Also, anything that increases the viscosity (thickness) of the beer should prevent the foam from disappearing. Since viscosity increases with decreasing temperature, cooler beer has better foam stability. So, make sure you pour your beer at ice-cold temperatures.
Use carbonation agents correctly.
Choose malts with a high protein content (e.g. crystal malt, dark malt).
Avoid low-protein adjuncts (e.g. corn, rice, sugar).
Wheat malt and flaked barley can increase the persistence of the head.
Bitter hops help the formation of the head.
Thoroughly sterilize and rinse the equipment.
Mash at a high enough temperature, depending on the grain.
A nitrogen-CO2 mixture helps the stability of the head.
Avoid using oils and fats.
Make sure the glassware is clean.
Carefully weigh the amount of triggering sugar.
Serve the beer cold.
In summary, if you make sure to add as much head-enhancing agent as possible to your beer, you will end up with a delicious, beautiful-looking beer.
