Beer foam forms when dissolved gas leaves the liquid and becomes trapped in small bubbles. For those bubbles to stay together, carbonation is not enough: substances capable of stabilising their walls are needed. These include proteins from malt and hop compounds that concentrate on the surface of the bubbles and help maintain the structure.
That is why a beer can raise a huge head when poured and be almost flat a minute later. The opposite can also happen: a more discreet but persistent layer can form. Producing foam and retaining it are related properties, but they are not the same. Experiments on beer service confirm that conditions producing more initial foam do not always produce more stable foam.
Then there is another observation: the foam almost completely disappears, but a small white "island" remains in the centre of the glass. When investigating products used to reinforce foam, an important name appears: Tetrahop, also known as tetra. It is worth knowing what it really does before attributing every remaining patch of foam to it.
Where the bubbles come from
Inside a closed can or bottle, part of the carbon dioxide is dissolved in the beer under pressure. When the container is opened, pressure drops and the liquid becomes supersaturated under the new conditions: it contains more gas than it can hold in equilibrium. Part of that CO2 then begins to leave.
Bubbles usually grow from small pockets of gas trapped in irregularities in the container or in microscopic particles such as cellulose fibres. This mechanism is called nucleation. It explains the streams of bubbles that seem to repeatedly emerge from the same point in the glass: a new fermentation is not starting; that point simply helps release gas that was already dissolved.
Pouring speeds up gas release, but the amount of visible foam at that first moment still does not tell us how long it will last.
Why foam disappears
Freshly poured foam is changing from the first second. Its evolution combines several processes described in research on beer foam physics, such as A. D. Ronteltap's thesis at Wageningen University.
The first is drainage: some of the liquid between the bubbles descends and returns to the beer. The films separating the bubbles become thinner. Gas also moves between bubbles of different sizes, a process called disproportionation: some grow while others shrink.
Another process is coalescence. Here, the film separating two bubbles breaks and both merge. When ruptures spread, the structure loses volume and continuity. Part of the gas also escapes into the atmosphere. It is not accurate to describe this simply as "the foam evaporates": liquid drains, gas redistributes and films break.
The foam island in industrial beer: what does it have to do with Tetrahop?
The question is specific: after drinking or letting a beer rest, a compact little island of foam remains on the surface. Could it be related to a product added to stabilise foam?
Tetrahop is relevant because its function is documented: it improves foam retention and its adhesion to the glass. But two statements must be separated: that a product reinforces foam, and that one particular shape can identify its presence. The first is supported by technical documentation; the second needs additional evidence.
What is Tetrahop and why is it also called tetra?
Tetrahop Gold is a commercial BarthHaas product formulated with tetrahydro-iso-alpha acids, abbreviated THIAA. It is obtained from hop extract and contains derivatives of hop bitter compounds. It is not an aromatic hop variety, but a processed ingredient with specific properties. The manufacturer's documentation also includes "Tetra" among its names.
Its use is not limited to achieving a more persistent head. It also contributes bitterness and can improve cling or lacing: the foam marks left on the glass while drinking. Those marks on the wall are different from an island floating on the liquid.
Tetrahydro-iso-alpha acids also show resistance to the degradation that causes the characteristic lightstruck defect. That does not mean adding tetra automatically makes any beer immune to exposure: the technical sheet requires considering the other bittering compounds present.
Does the island prove that a beer contains tetra?
No. The technical sheets consulted describe improvements in persistence and adhesion, but they do not present the formation of a central island as a method to identify the product.
The distinction is clear in Hopsteiner documentation, another manufacturer of this type of extract. To determine tetrahydro-iso-alpha acids in beer, it indicates analysis by high-performance liquid chromatography, or HPLC. To evaluate foam, it describes other methods that measure stability or adhesion. These are different measurements: one studies chemical compounds; the other studies foam behaviour.
A particularly persistent foam is therefore compatible with the effect of tetra, but appearance alone is not enough to attribute it to a specific beer. And an analysis detecting THIAA would identify those compounds, not necessarily a particular commercial brand.
The useful answer to someone searching for "industrial beer foam island" is not to ignore Tetrahop or claim every island reveals it. It is to explain that the product exists, that it modifies retention and that observing a glass is not a substitute for manufacturer information or analysis.
Tetrahop is not the same as E405
E405 is propylene glycol alginate, a different substance. It is also used in products designed to stabilise foam: Drifoam by Lallemand is one commercial example based on that ingredient, derived from alginic acid.
The confusion is understandable because both can help maintain foam, but they are not interchangeable names. Tetrahop is a hop product; E405 identifies another compound. When the question refers to "tetra" or the hop derivative, answering only with alginate leaves out the product being sought.
A lot of dry hopping does not guarantee longer-lasting foam
In a craft-focused shop, this matters. An IPA can contain a huge hop load and still retain less foam than another less heavily hopped beer. The effect depends not only on how much hop is added, but also on the variety, the timing and the contact time.
A 2018 study by Hopsteiner researchers John Paul Maye, Robert Smith and Jeremy Leker, published in BRAUWELT International, examined the effect of dry hopping. In their trials, increasing the dose of Cascade or prolonging contact could reduce foam stability. But the result was not identical with every variety: Apollo and Eureka! improved stability under certain test conditions.
Another study, published in BrewingScience in 2019 by Cocuzza and collaborators, worked with a pale ale divided into vessels with increasing amounts of Cascade T90. The researchers observed a decrease in foam stability and iso-alpha acids, along with changes in other parameters such as pH and polyphenols. These are results from one beer and one protocol, not a general condemnation of dry hopping.
The important point is that dry hopping is not simply adding aroma to a beer that remains unchanged. It can modify composition and remove some compounds through interaction with plant material. The idea that "more hops means better foam" does not describe well what happens in an intensely hopped IPA.
Nor should it be replaced by "hop oils destroy foam". Different results between varieties show that explanation is too simple. Maye and collaborators even found that tetrahydro-iso-alpha acids could recover stability lost after dry hopping. Tetra therefore also appears in research aimed at brewing problems relevant to craft breweries.
Dark colour and body do not guarantee good retention
A dense beer can give the impression that it should hold an equally dense foam. However, body, colour and foam stability are not the same property.
Combe, Ang and Bamforth compared different cereal products in a study published in the Journal of the Science of Food and Agriculture. They found important differences: wheat malt showed favourable characteristics, while some crystal malts contained components with a net negative effect. Black malt extracts and roasted barley, on the other hand, could offer good foaming properties.
This helps avoid two simplifications: that any specialty malt improves foam and that a very roasted ingredient necessarily harms it. Composition matters, not only colour or flavour intensity.
Alcohol and certain lipids can also reduce stability. That does not mean all high-ABV beers should immediately lose their head, but that the recipe brings together factors that can help or hinder foam at the same time. Evaluating an imperial stout only by comparing it with a light beer ignores part of that balance.
There is no single "foam protein" that explains everything
A 2025 study in Physics of Fluids examined the films separating bubbles in different beers. It found different stabilisation mechanisms: surface mechanical properties played an important role in some samples; in others, liquid movements associated with differences in surface tension also mattered.
The study related those behaviours to the proteins present and their modifications, including LTP1. The useful idea is not to memorise an acronym: it is to understand that total protein quantity alone does not explain persistence. Its state and behaviour on the bubble surface also matter.
The glass can change the result of the same beer
A beer can be well made and still lose foam because of what it finds in the glass. Traces of grease, oil, detergent or cleaning products can alter stability even if the glass looks transparent and has no visible stains. That is why Cicerone distinguishes between a visually clean glass and one suitable for beer service.
One indicative check is to wet the inside and empty it. Water should run off as a continuous sheet. If it gathers into drops or leaves irregular paths, washing should be reviewed. Irregular bubbles clinging to the walls can also warn of residues, although no single observation replaces good cleaning.
At home, washing beer glasses with greasy plates can introduce contamination. Drying them with a cloth does not always help either: fabric can transfer oils or fibres. Cicerone's home guide recommends careful washing and rinsing and letting glassware air dry.
To investigate unexpected foam loss, it is worth making a simple comparison: pour the same beer into two identical glasses, one prepared as usual and another carefully washed and rinsed. Keep temperature, volume and pour similar. If behaviour changes consistently, you have a reason to review the glassware.
That comparison does not detect tetra or evaluate overall beer quality. It checks a variable that is often overlooked.
Temperature and pouring also count
A beer that is too warm can release gas more easily during service and produce a large amount of initial foam. In experimental work by Lyu and collaborators, published in Physics of Fluids, higher temperature and serving pressure favoured foam formation, but not necessarily stability. A very intense gas release and a persistent head are not the same thing.
For many packaged beers, a reasonable starting point is to tilt the glass about 45 degrees, pour initially down the side and gradually straighten it. The final intensity is adjusted to how the beer responds. There is no need to impose exactly the same foam height on products with different carbonation and characteristics.
A frozen glass is not a universal solution either. Cicerone service documentation warns that it can generate excessive foam, chill the drink too much and retain frozen residues of cleaning products. Frost is not a substitute for washing.
The aim is not to prevent every bubble from appearing or to fill half the glass with foam. It is to serve in a controlled way and adapt the gesture to the beer in front of you.
What foam tells us and what it does not
Foam provides information, but the question must be framed well. "Why is this beer losing its head so quickly today?" allows investigation of the glass, temperature, service or differences between batches. "Is it bad because it has little foam?" tries to summarise too many variables in one observation.
Nor should the term craft be used to justify every unexpected behaviour. Foam that disappears immediately may deserve review. What it does not allow is deciding, without more data, where the problem lies.
The same applies to Tetrahop. Knowing it exists helps explain why foam persistence can be technologically adjusted. It does not authorise identifying it by a white island, assuming all industrial beers use it or assuming no craft brewery can use it.
The important distinction is between observing and proving. We can observe a compact head, marks clinging to the glass or a small central island. To explain its origin, we need more than its shape.
