Head, froth, foam call it what you will, a nice layer of creamy foam on top of a pint of beer is a key part of what makes a good beer, although it could be argued whether it makes any difference to the flavour and aroma of your pint. I think it definitely has a psychological, aesthetic and texture (mouthfeel) benefits that mean achieving a good level of foam on top of your home brew benefits the drinker (there is a particulary good section in Tap into the Art and Science of Brewing regarding this point). The factors that produce good foam and head retention are complex but here we will look at some simple variables that both help and hinder this quality.
Beer Foam Destroyers
One sure fire way to serve a beer with poor foam and head retention is to pour it into a dirty glass. Well, when I say dirty glass what I mean is a glass that has either not been rinsed properly of some detergent/sanitizer or has oily residues from things like bar snacks or lipstick.
Lipids
Fats and oils otherwise known as lipids are an active foam destroyer. If you regularly drink at a bar or pub and enjoy the snacks that go hand in hand then there is plenty of opportunities for these lipids to destroy the foam on beer. Washing your glasses in dirty dishwater that has had other washing in is another way to leave traces of fat and oil.
There are also lot of soaps and sanitisers that leave residue of compounds that result in a collapsed head, rinsing your beer glasses thoroughly and drying will avoid this with your home brew
It is also worth mentioning here that if you add anything to your beer other than malt, hops, water and yeast to consider what it’s going to do to the head of the finished brew. A common addition is chocolate for example which contains a lot of fats which are definitely going to destroy foam. Another ingredient which is more commonly used in stouts are oats which are also high in lipids.
Head Retention and Head Forming Qualities
The nature of beer can dictate it’s foaming qualities, most important for froth formation are protein compounds. Generally the higher level of proteins in the beer, the better for froth. If you brew all grain you will know that generally when you dough in, a fair amount of foam forms from the stirred malt. So we know the malt is a good source of protein good for producing nice creamy heads on beer, selecting malt high in protein has been a favourite thing for brewers to do. This is why you see a lot of home brew recipes with 5-10% wheat malt added, wheat malt is one of the grains that contains higher amounts of proteins.
The malt that is available to brewers today is generally well modified but differ from one variety to another, a fully modified malt will have had more protein degradation than a less modified one. Some beers you brew may be more prone to having a good layer of foam because the malt is less modified and contains better head forming compounds. Try and do a little research into the malt you buy and find out from the producers these bits of information, you will have a clearer idea of whether your malt is going to result in a frothier beer.
Carbonation
Carbonation is a clear cause for beer foam, you will know that the way you pour a beer will also effect the amount of foam. As a general rule the higher level of carbonation the more resulting froth on your beer, carbon dioxide escaping from solution will ensure head formation but the other properties mentioned here will dictate how long it sticks around. As for pouring the beer the amount of air you get into the beer as you pour it will increase the size of the head. Glasses will again have a part to play, a tulip shaped glass is often used for certain Belgian beers to stabilise and support the head and are often served in a ratio of 50% beer, 50% foam. Some breweries also etch glasses to promote foam production, the etchings act as a catalyst for bubbles to form.
There are a lot more complexities around beer head and the nature of what causes it but hopefully this introduction will give you a little more understanding of what’s going to effect it in your home brew.
