Beer Foam: Why Beer Has a Head and How to Get a Good One

Beer foam, called the head, is carbon dioxide gas trapped in bubbles whose walls are made of malt proteins and hop compounds. When you pour, dissolved CO₂ comes out of solution and rises as bubbles. In water they would pop at once. In beer, proteins from the barley and bitter acids from the hops coat each bubble and hold it together, so the bubbles stack up into a stable head.

Why beer foams

Beer is carbonated: it holds CO₂ dissolved under pressure. Open the bottle or pour from the tap and the pressure drops, so the gas starts to escape. Bubbles form on tiny imperfections in the glass (nucleation points), grow as they rise, and collect on the surface.

Whether that foam lasts depends on what the beer contains:

• Proteins from malt, especially one called LTP1 and a group of mid-sized proteins, are the main foam builders. They gather at the surface of each bubble and form an elastic skin.
• Iso-alpha acids from hops, the same compounds that make beer bitter, bind to those proteins and strengthen the bubble walls. That is part of why hoppy beers often hold a thick head.
• Carbonation level. More dissolved CO₂ means more gas to form bubbles.

What gas makes beer foam?

Carbon dioxide, in almost all beer. Nitro beers, such as many stouts on draught, are dispensed with a mix of nitrogen and CO₂. Nitrogen barely dissolves in beer, so it forms much smaller bubbles, giving the dense, creamy, long-lasting head and the cascading effect in the glass.

Is beer foam good or bad?

A good head is a good thing. About one to one and a half inches (2 to 4 cm) of foam on a pour:

• Carries aroma. Bursting bubbles release hop and malt aromatics right under your nose.
• Improves mouthfeel. Foam softens carbonation bite and gives a smoother first sip.
• Shows the glass is clean. Foam collapses quickly in a glass with grease or detergent residue. Rings of foam left down the glass as you drink ("lacing") are a sign of a clean glass and a well-made beer.

Pouring down the side of a tilted glass and straightening it at the end gives a controlled head. Pouring with no head at all traps more CO₂ in the beer, which can leave you feeling bloated.

What improves head retention

Helps foam	Kills foam
Wheat, oats, rye and dextrin or crystal malts in the grist	Grease, oils and lipstick on the glass
A firm hop charge (iso-alpha acids)	Detergent or rinse-aid residue in glassware
Correct carbonation for the style	Under-carbonation or flat beer
A vigorous boil and a good hot break	Long protein rests that break down foam proteins
Healthy yeast and a clean fermentation	Stressed or autolysed yeast, which release foam-damaging enzymes
Clean, beer-only glassware, rinsed cold before pouring	Some fining agents and heavy filtration, when overdone

Carbonation and foam

Carbonation is measured in volumes of CO₂: one volume means the beer holds its own volume of CO₂ gas. Style targets:

Style	Volumes of CO₂
British cask-style ales	1.5 to 2.0
Stouts and porters	1.8 to 2.4
American ales and IPAs	2.2 to 2.7
Lagers and pilsners	2.4 to 2.8
Belgian ales	2.5 to 3.5
German wheat beers	3.0 to 4.0

In a keg or a pressure-rated fermenter, carbonation is set by temperature and pressure. As a reference, about 11 to 12 psi at 38°F (3°C) gives around 2.5 volumes. You can reach it by setting the pressure and waiting a week or so, by using a carbonation stone to carbonate in a day or two, or by fermenting under pressure with a spunding valve so the beer carbonates itself as it finishes.

Too much foam from the keg?

If every pour is all foam, the usual causes are:

• Over-carbonated beer: pressure set too high for the temperature.
• Beer too warm: warm beer holds less CO₂ and releases it in the line.
• Beer line too short for the pressure: the beer arrives too fast. Longer or narrower line adds resistance.
• Warm tap or tower: the first pour foams, then it settles.
• Infection: bottles or kegs that keep gaining carbonation over weeks may have a wild yeast or bacteria problem.

Foam on fermenting beer

The thick, frothy foam on top of beer during fermentation is called krausen. It is completely normal: CO₂ from active yeast, carrying proteins, hop resins and yeast to the surface. It usually appears within a day of pitching, peaks after two to four days, and falls back into the beer as fermentation slows. A fallen krausen is a sign that primary fermentation is nearly finished.

• Krausen coming out of the airlock? Use a blow-off tube, leave more headspace (about 20 to 25% of the fermenter), or ferment a little cooler.
• Fermenting under pressure keeps krausen much smaller, which is one reason brewers ferment in pressure-rated tanks like the Unitank. Our pressure fermentation guide explains how.
• No krausen at all? Some yeasts and some lager fermentations produce very little. Check the gravity rather than relying on foam.

Frequently asked questions

What is beer foam called?

The head. The foam that forms on fermenting beer is called krausen, and the lines of foam left on the glass as you drink are called lacing.

Why does my beer have no head?

Most often a dirty glass (grease or detergent residue), low carbonation, or a recipe low in foam-building proteins. Adding a little wheat, oats or dextrin malt and getting carbonation right usually fixes it.

What gas is responsible for beer foam?

Carbon dioxide in most beers. Nitro beers use a nitrogen and CO₂ mix, which gives smaller bubbles and a creamier head.

Is it bad to drink beer foam?

No. The foam is just beer and CO₂. A proper head improves aroma and mouthfeel.

Why does beer foam when you open it warm or shaken?

Warm beer holds less CO₂, and shaking creates countless tiny bubbles that act as nucleation points. Both make the gas escape all at once.