A head holds because beer is full of dissolved protein, and bubbles rising through it collect that protein on their surface and bind to it, which is why a beer built on a high protein malt keeps a foam while a stripped lager does not. Everything that survives contact with a glass decides how long that foam lasts, and the variables are few enough to hold in your head, namely the height you pour from, whether the glass is clean, how warm the glass is, and what you ate before you drank. The most reliable of them is also the one most people ignore, since a glass washed with detergent and not rinsed under the tap will never hold a foam no matter how well the beer is poured.
Why A Head Exists At All
Foam is not carbonation itself but a structure built out of it. When a bubble forms on the inside wall of a glass, it rises, and the rising surface collects dissolved high molecular weight protein from the beer, which unfolds at the gas to liquid interface and re-folds into a film. That film is what stops the bubble from merging with its neighbour, and a bubble that merges becomes a bigger bubble, which rises faster, and the loss of the film is the point at which the head collapses. The other half of the structure is hop resins, since the alpha acids in the beer are surface active and get dragged to the interface along with the protein, and this is the mechanism behind the well known observation that a heavily bittered beer holds a head remarkably well while a mild one often will not.
This is also why a head is worth protecting rather than skimming off out of habit. The film of gas and protein sitting on top of a beer is a barrier between the liquid and the air, and it slows the carbon dioxide escaping from the glass and the oxygen coming in. Drink straight from the bottle and you lose the head, the beer goes flat faster, and the aromatics that were in the head space are gone with it. The most striking version of this is an imperial stout, where a head left in place for a few minutes measurably changes how much of the roast and chocolate aroma you can still smell when you come back to the glass.
What The Glass Is Doing
Glass is not a passive container, because a clean glass has a charged surface that attracts the protein film and a dirty one has an oily surface that repels it, and that single difference accounts for most of the bad pours people complain about. Detergent, fat from a fingerprint, and a trace of dishwater all leave a film that stops the bubble wall from adhering, so the gas escapes without building structure. Rinse the glass in cold water without detergent after washing it and the problem disappears. Beyond cleanliness, the shape of the glass controls the rate at which the foam survives, since a narrow taper at the bottom gathers the bubbles up into a tight column where they press against each other and hold, while a very wide bowl spreads the same liquid over more surface and gives the head nowhere to sit.
| Factor | What it changes | Which direction you want |
|---|---|---|
| Glass washed with detergent | Blocks protein adhesion on the inner wall | Rinse without detergent |
| Fatty or oily glass | Same effect, worse and harder to see | Never pour into one |
| Bubbles made in a clean glass | Adhere, forming a stable film | What you want |
| Bubbles made in a dirty glass | Bounce off, merge, and escape as air | Why the head never forms |
| Nitrogen or added gas | Very small bubbles, creamy and dense | Creamy but heavy mouthfeel |
| Carbohydrate or malt addition | Raises dissolved solids, thickens the liquid | Improves hold and body |
How To Pour One That Behaves
The pour that people call correct in a taproom is really a two stage move, and each stage is doing a different job. Tilt the glass to about forty five degrees so the beer runs down a clean wall rather than onto the bottom, and start low, letting the liquid build a shallow pool in the base while the first bubbles are still large. Then raise the glass towards vertical and pour the remainder down the middle in one steady stream, which drives the coarse bubbles out through the foam and leaves the finer ones behind. The result is a head that is dense, tight to the glass and a centimetre or two thick rather than a large, loose cap of half-inch bubbles that collapses before you have picked the glass up.
The other half of technique is temperature, both of the beer and of the glass. A warm glass gives you a thin head because the gas comes off faster through the warm wall, so a glass taken out of a warm cupboard in summer will underperform the same beer poured into a cold one. A cold glass taken straight from a fridge also has condensation on the inside, and water on the wall is not a neutral surface, so wiping the inside of the rim is worth doing even on a cold day. Leave the glass out for a moment so the wall warms toward the beer rather than freezing it, and you will find the head holds noticeably longer than it did straight from the fridge.
What The Beer Itself Brings
Two things in the liquid decide how much structure there is to build with, and neither is adjustable by the person drinking. The first is the concentration of dissolved high molecular weight protein, which comes mainly from a grist with a decent share of malted wheat or a light kilned malt, and it is why a hefeweizen, an English bitter or a nitrogen-charged stout will hold a head far longer than a stripped pilsner from the same brewery. The second is dissolved carbohydrate, since sugars and dextrins thicken the liquid and slow the coalescence of small bubbles into large ones. A brewery that wants a stable head therefore has three levers, which are the malt bill, the addition of a hydrolysable starch or sugar syrup, and the choice of gas.
The choice of gas is the one that produces the biggest visible difference and the one that changes the beer rather than the foam alone. Carbon dioxide forms bubbles quickly, and they rise in a lively, aggressive column that looks like a sparkling wine. Nitrogen dissolves far more slowly and forms much smaller bubbles, so a nitrogen charged stout pours with a dense, smooth, almost solid-looking head that sits like a cap and barely moves, and the drinking experience is creamy and dense rather than sharp. Nitrogen is not a substitute for carbonation in every case, because it does not carry the same crisp bite on the tongue, and a brewery that wants both uses a blend. If you have never tasted the same stout on one and then the other, the difference is the most immediately obvious thing about head retention that you can find in a glass.
The Part You Control, Which Is Not The Pour
Fat is the enemy of a good head, and this is the part that surprises people, because the effect is immediate and it is nothing to do with the beer. The lipids in butter, oil, cheese and rich meat coat the inside of the glass in a film that behaves exactly like detergent, and a glass that has held a slice of pizza has no chance of holding a foam. It also coats the surface of the liquid itself, which stops the bubble film forming, so the head collapses faster and the beer arrives in the mouth with less aromatic surface to smell. Waiting a few minutes for the glass to be rinsed by the beer, or drinking from a wider glass where your mouth does not touch the rim, both work around it.
- Rinse every glass after washing it, with cold water and nothing else, since a single trace of detergent is the most common reason a head will not form.
- Never drink from a glass that has held fatty food, and if you have, rinse it before pouring into it rather than assuming the pour will save the head.
- Pour down the side of a tilted glass and then raise it, which gives a tight, dense head rather than a loose cap of large bubbles.
- Let the glass reach the temperature of the beer, and wipe the inside of the rim where condensation collects.
- Choose a shape that tapers, since a narrow base gathers the bubbles into a column and gives the foam something to hold onto.
- Do not skim the head off, because it is the barrier that keeps the carbonation and the aromatics in the glass.
Read The Head Before You Drink
Once you know what the foam is made of, it becomes a useful diagnostic rather than a matter of taste, and you can read a beer before you have swallowed any of it. A dense, tight, off white head that stays put suggests a beer with body, with protein from the malt bill and with enough residual carbonation, and it usually correlates with a beer that will also have a good mouthfeel. A large, coarse, fast-vanishing foam that leaves a ring on the glass usually means a thin, highly carbonated beer, which is not a fault but does mean the aromatics are escaping quickly. A head that forms and then flattens to a thin lace across the bottom within a minute is telling you the liquid is thin and the glass is dirty, and that is a pair of facts you can act on the next time you are ordering.
None of this is decoration. The head is the part of the beer that is still gas, protein and aroma rather than liquid, and it is the reason a glass of well poured stout on a cold day in a Victoria pub in December tastes like more than the same beer poured badly in a warm room in July. Our piece on bottle conditioning covers where the gas in that head came from in the first place, and if you want the vocabulary for what you are smelling once the foam has settled, the tasting glossary will get you through it.
