The aesthetic of drinking beer is to an extent subliminal. The presentation of beer in a glass with its foam head, clarity and colour conjure Pavlovian anticipation for the perceptive drinker. It is said that a beer drinker drinks as much with their eyes as with their mouth.

That foamy head confers not just a visual benefit. It also acts as an efficient gas exchange surface pitching aromas towards the drinker’s olfactory sensors and so provides a drinker’s first tantalizing glimpse as to the quality of the beer’s flavour, freshness, refreshingness and wholesomeness.

Foam is also tactile to the lips and affects mouthfeel through its stability and its structure (bubble size).

But what are the features of good foam quality? Typically, this is defined by a combination of its stability, quantity, lacing (glass adhesion or cling), whiteness, “creaminess” and strength. Here beauty is definitely in the eye of the beholder as consumers discriminate between beers based on their foam characteristics. These choices have been found to diverge between genders, race or even region.

Figure 1: Comparison of the small bubble size from nitrogenated foam vs the coarser bubble formed with carbonated beer.

The world is split between consumers who like to see stable (but not excessive) head on the beer but a clean glass at the end of drinking and those who prefer to be left with a lacing pattern on the glass. More recently, it was demonstrated that men generally rate foam lacing higher than women.

Foam stability is the result of the interaction between the proteins from the malt and hops. Most modern Australian varieties of malt such as Gairdner Flagship, Baudin, and Commander have high levels of the protein Z4 compared to older varieties such as Schooner and Stirling. Isomerised hop-α-acids, which provide the bitter taste of beer, have also been demonstrated to be foam promoting, especially in their hydrogenated forms such as “Tetra” hop. The tetra hop form was primarily developed to provide protection from light strike – or what the Americans call “skunking” – in beers sold in the less protective but visually attractive clear or green glass bottles.

While contributing to a crisp and dry final product popular with many drinkers, the practice of using cane sugar in brewing dilutes out the foam proteins that contribute to a highly stable head. To counter this, many brewers can add the chemical propylene glycol alginate (PGA). Adding PGA is reputed to increase foam stability by around 5-10% and many brewers rely on it to provide satisfactory foam quality for some of their products.

Figure 2: Top: A selection of foam generating widgets. Middle: Small amount of fob formed at the opening of widgeted can. Bottom: Initial pour of widgeted can providing the theatre of numerous small bubbles rising to form head.

Other strategies for promoting foam stability involve the use of devices added to the packaging or included in the glass. The most technically simple is the use of “nucleated” glassware such as the “head keeper or head master” style that can be found in many Australian pubs. Through the use of microscopic abrasions on the bottom of the glass, this “energised” glassware produces new bubbles that replenish collapsed bubbles in the foam head. The process also results in “beading” which is the attractive spectacle of the bubbles rising from the beer up to the foam.

While most beers are naturally and conventionally carbonated, the use nitrogen gas also improves foam stability. Nitrogen has a lower partial pressure compared to CO2 and results in the production of smaller, more stable bubbles (Figure 1, right). This is the creamy and stable head typically associated with a pint of Guinness.

The addition of nitrogen into the beer changes the foam’s mouthfeel to a “creamy” texture, however the lower CO2 content leads to beer with less “prickle” (acidic feeling from bubble collapse) on the palate making the beer taste flat and watery. Still, tests have shown that the visual impact of the foam head on a glass of beer is more important than the tactile impact on perceptions offlavourand mouthfeel and the brewer’s use of nitrogen depends on the beer style and consumer preferences.

The use of the widget is relatively widespread in some styles of beer. It is either attached to the base of the package or floats within it. These characteristics reduce the appeal of the widget in the more popular bottle, presumably because the sight of a widget floating or attached to the bottom of a bottle is somewhat disconcerting for the consumer.

In cans, the widget can be commonly found in the less carbonated stout and bitter ale style beers of the United Kingdom, such at the cans of Guinness, Boddingtons ale and Newcastle Brown ale, but has not found acceptance in other regions or beer styles. Next time you have a can of one of these beers, cut the can open and observer the technological marvel inside (be careful not to cut yourself).

Figure 3. Perceptions:
“Lively beer with a good head”
“Ripped off, foam is not beer”
“Will this foam wreck my lippie?”

The nitrogen widget was designed to emulate the draught style of UK pub presentation (Figure 2 right, a selection of widgets). Widgets work as nitrogen foam nucleating devices and in some cases the widget can also form bubbles from its nucleated surfaces. The widget also provides a degree of theatre on package opening with a characteristic rumble of the gas being released through the widget vent to produce a slight fob at the package opening (Figure 2 middle) and pour associated with the rise of a multitude of tiny bubbles to a creamy head (Figure 2 bottom).

The main downside of widgets is that they are considered by the industry to be expensive both in terms of capital and consumable costs.

Foam quality, however, is not just about “quick” fixes such as the inclusion of widgets, ever greater levels of “tetra” hop or gas composition but attention to the beer making process from grass to glass (malting variety breeding to dispense. Brewers do have solid options in manipulating the quality and quantity of malt foam positive proteins and selection of hop acids, the interaction of which provides the basis for foam stability and quality.

Figure 4: Perceptions
“This beer’s flat”
“Ahh that’s more like it, a full measure”
“Not a very lively and appealing beer”

Brewers also have a range of palliative options such as additives, gas composition, widgets and methods for dispense that can be used if suitable to the style of beer being produced.

Beauty is however very much in the eye of the beholder. This is very true for foam too. The expectations for foam differ between race, region and gender. The “Pope of Foam”, Charlie Bamforth, was the first to identify that “there is a divide between consumers who like to see stable (but not excessive) head or foam but a clean glass at the end of drinking and those who favour a lacing pattern on the glass”.

It has been demonstrated that men generally rate foam lacing higher than women. In addition, a female colleague pointed out the “obvious”. Some women tend to be adverse to foam because the thought of its adherence to their lips is unsettling, in that it could spoil their carefully applied make-up. Overall, these quandaries can perhaps be simply outlined pictorially as shown in Figures 3-5.

At a professional workshop I conducted in 2010 on beer foam, I asked the more than 30 attendees to fill out a pop quiz about their attitude was towards foam. This workshop included a selection of major American major, craft brewers and beer researchers. Interestingly, 75 per cent of the respondents liked lacing and on average preferred a foam depth was 2 cm. A surprising result was that 34 per cent of the survey respondents had rejected or sent back beer in a restaurant or bar because the foam was poor.

Figure 5 – Perceptions:
“Great lacing, an excellent beer”
“A dirty glass”
“This glass hasn’t been properly cleaned”

I too believe that beer drinkers should be served beer with a generous amount of foam that is appropriate to the style of beer being served. Thus if the presentation of your beer is not good enough, send it back! The serving staff and the owner will quickly get the right message!

Dr Evans’ brewing quality research is being applied in Australia’s malting barley breeding programs (Adelaide and Perth) to provide maltsters and brewers with the best possible barley for brewing. This is an edited extract from the book chapter that contains these details and more from: Handbook of alcoholic beverages: Malting and Brewing, Bamforth, C.W., Russell, I., and Stewart, G.G., Editors. Evans, D.E., and Bamforth, C.W., Beer foam: achieving a suitable head, Elsevier Burlington, MA. Chapter 1, pp 1-60, 2009.

For further details visit: www.books.elsevier.com.