Is yeast presence a major head retention inhibitor?
Q: I’ve been trying to improve the head retention of my batches and have not had much luck. I recently brewed a dry stout with wheat malt and flaked oats, and I also increased the corn sugar amount for priming with visions of a thick, creamy, long-lasting head. But alas, it was not to be. When I pour the beer into my Murphy’s Irish Stout pint glass, I initially get a nice head, but this disappears within 30 seconds. After a minute or so, the beer actually appears completely flat. Is yeast presence a major head retention inhibitor? Also, I read Chris Colby’s piece “Balanced Recipe Formulation” (March-April 2007) where he states that adding wheat to a recipe in an effort to improve head retention should not be substituted for sound brewing practices. What exactly are those brewing practices and what are the things that would increase or decrease head retention?
— Chris Adams • Miami, Florida
A: Good foam is something that many brewers like on their brews for aesthetic and mouthfeel reasons. Foam looks appetizing on top of a pint of brew and also adds texture to the beer when drinking. Some draught beers have really creamy foams created by using nitrogen to froth up the beer. We use nitrogen for certan styles at Springfield Brewing Company and I love the effect on some beers, but getting great foam on a nitrogen-dispensed beer is much easier than from a carbonated beer.
There are several things that can cause beer foam to be less than remarkable. Some of the real foam killers frequently seen in brewing are compounds that actively cause beer foam to collapse. Most of these substances have one thing in common and that is that they congregate on the surface of the beer and compete for space with beer foam at the gas-liquid interface.
Lipids (fats and oils) and surface-active cleaners/sanitizers are two types of substances that really do damage to foam. While lipids usually do not come from brewing ingredients, they are frequently found on beer glasses that have either been soiled by lipstick or dirty dishwater. This is really more common than most people think when drinking beer at a bar. You can also transfer grease to a beer glass when you are munching on oily snacks — for example, peanuts or potato chips — while sipping a beer.
Most soaps and sanitizers have surfactants to aid in their effectiveness and residuals of these compounds can cause foam problems. This is one reason that it is so important to rinse cleaners from brewing tools. If you use non-rinse sanitizers, it is very important to make sure that your sanitizer of choice does not damage beer foam. If you are not sure whether you’re using a sanitizer that damages foam you can do an easy test. Rinse one glass with water and one glass with sanitizer. Allow both glasses to drain upside down for 15–30 seconds so the surface is not completely dry. Pour a half bottle of beer from the same bottle in a similar fashion into both glasses to ensure foam formation and watch. If the foam in the glass rinsed with sanitizer crumbles like the Berlin Wall you’re using a wicked sanitizer!
The beer itself has intrinsic properties that dictate the ability for good foam formation. In my experience with foam, the most important foam positive constituents of beer are proteinaceous compounds from the malt. Although the use of under-modified malt in brewing comes with a whole set of issues and is really hard to find, the breakdown of barley proteins during germination is limited and there is a relatively large amount of foam-positive protein in the malt. In contrast, well- and over-modified malts are fairly common and protein degradation in these malts is more extensive during malting (protein degradation is one of the key parameters used to gauge modification).
The bottom line is that malt modification affects foam and most of the pale malt on the market today is well-modified and has less foam positive proteinaceous goodies than lesser modified malt. Some brewers have strong feelings about the importance of proteolytic activity during mashing; there are those who know it happens and how it affects beer and those who know that it really doesn’t happen and see it as a waste of time. Believers in proteolytic activity during mashing caution against a long rest around 122 °F (50 °C) because it can reduce the foam quality of the resulting beer.
Adding some wheat malt to a brew can make up for the deficit in foam-positive proteins from barley malt because wheat malt contains much more foam positive compounds compared to barley malt. Although many recipes call for a small amount of wheat malt (about 5%) intended to improve foam, I have never found that this small amount does much for the beer. Our best seller is an unfiltered American-style wheat beer made using about 50% wheat malt and about 7% raw wheat. This beer has a very different foam appearance and stability compared to our all-barley malt beers.
Our unfiltered wheat also contains yeast and I have never noticed much of a change in foam stability over time after bottling. Yeast can cause problems with beer foam over long storage periods because when yeast die and autolyze, enzymes spill into the beer. Proteolytic enzymes are included in this spilling and degrade foaming proteins in the beer. As you mention in your question, Belgian beers are known for really nice foam, and they are normally bottled conditioned. I do not think your foam problems come from yeast in the bottle.
In addition to protein, hops are also considered foam positive because beers brewed with almost no hops have poorer foam stability compared to beers brewed with perceptible bitterness. This is more of a laboratory-type observation and most beers have enough hops to benefit from their foam positive nature. Adding more hops to improve foam affects flavor and while it is true that really hoppy beers often have good foam I cannot recommend using hops as a foam enhancer and a solution to bad foam in general.
The gas content of beer, normally carbon dioxide, clearly influences foam because there would be no foam without gas evolution upon dispense. Carbon dioxide content primarily influences foam volume and not foam stability. So if you increase the carbon dioxide content of beer, you may have more foam initially but the rate of collapse will not be affected. Like adding more hops I don’t suggest adjusting your carbonation rate based on improving foam; the carbonation content affects flavor and you should shoot for a target in-line with the beer you are brewing.
Some beer glasses contain little etched spots in the bottom that act as nucleation sites for bubbles to form. This causes the continual formation of foam while the beer sits in the glass and new foam formed replaces foam that has collapsed. Some people add a few pieces of coarse salt to the beer and these little chunks of salt do the same thing as the special etched spots. Samuel Adams (Boston Beer Company) recently came out with a special glass they developed to enhance the presentation of their beers and one of the design features is a little etched spot in the bottom.
There are some ingredients used in certain brews that are believed to either be outright foam negative or at least have the potential to be foam negative. One common theme of such ingredients is the presence of lipids and examples include flaked oats, chocolate, coffee, vanilla, nuts and other nutty brewing ingredients. Although these ingredients contain more oil than malted barley (sometimes considerably), they do not necessarily cause foam problems. They can, however, and brewers need to look out for problems when using such ingredients. Your stout contains flaked oats and many brewers believe that oats cause foam problems.
I think what Chris Colby meant when he stated that adding a bit of wheat malt should not be a substitute for sound brewing practice is that there is not a silver bullet to brewing beer with good foam. All the factors that affect foam must be considered to appease the foam gods.
