Dear Mr. Wizard,
For the past few batches I have been having difficulties with carbonation and head retention. I brew all-grain and recently brewed an oatmeal stout. Anticipating the problem, I mashed a half-pound of wheat to help. I bottled when the batch reached 1.024 with 3/4-cup of corn sugar. After my two weeks in bottle, I was expecting a nice, fine frothy head. When I opened it, I heard the tell tale hiss of carbonation. But when I poured it into a clean glass, almost no head. I thought by brewing a stout, along with the wheat addition, I would be okay. What can I do to solve this problem?
San Jose, California
Mr. Wizard replies:
Beer foam is one of those things that seems to come magically when things are going right. Just as it can come without doing anything special it can also be frustratingly absent even when trying to lure it atop of a brew. The foam formula is really simple; you need to have foam-positive proteins and carbonation to produce beer foam. Hop acids improve lacing and highly hopped beers typically have better foam adhesion to the glass than those with lighter hopping. Foam is affected in a negative way by oils, fats and certain sanitizers. Oats contain considerably more oil than barley or wheat, and oats are frequently cited as foam- negative. Thus, it is highly probable that this is the problem with your stout’s carbonation.
Foam seems so simple when explained briefly. It seems that any all-malt beer should produce good foam, but that is not the case. Although all brewers like to talk about foam, the reality is that some beers have better foam than others. Belgian, German and Czech beers all have great foam. Certain beers in England have good foam, but pints served in London have been known for being served with little if any foam because of local preference. I believe the foam found on cask beers is largely influenced by beer dispense. Nitrogen (from air “sparklers”) is primarily responsible for the type of foam found in British ales. Continental beers have fluffier, drier foams that at times look like meringues.
One key difference between traditional British ales and continental lagers and ales is the type of malt used. Malts produced from barley grown on the British Isles are known for even and complete modification, whereas continental malts are known for their low level of modification. These differences explain why British brewers traditionally use infusion mashing and the European brewing tradition uses decoction and step mashing. While fully modified malts certainly are easy to mash, they do have different “proteins” than malts that are not as modified.
I put “proteins” in quotes because there are no native, malt-derived proteins found in beer. There are all sorts of polypeptides, formed from the breakdown of these proteins, with different sizes and properties. Although the entire foam story has not been completely explained by brewing researchers, most agree that foam-positive polypeptides are medium to large molecular weight molecules (25– 100 kiloDaltons) with a strong hydrophobic character. It is also generally believed that under-modified malts contain more foam goodies than do fully or over-modified malts.
So what does this all mean? Brewers of all sizes sometimes over look the importance of their base malt. If you are brewing with fully modified ale malt, you may be getting the best foam you can from that particular ingredient. I brewed a Pilsner a few years ago with Briess Pils malt, which was new at the time. Although Mary Anne Gruber was as secretive about that malt as their Cara-Pils, she did tell me that modification was intentionally limited. The wort in the kettle had amazing white, fluffy foam as did the finished beer. Other than the malt and the hop variety, this recipe was very similar to our helles lager brewed with a fully modified pale malt. The foam quality however was markedly different.
You mention using malted wheat as a foam booster. A better ingredient for help with foam is unmalted wheat. Un-malted wheat can be milled and added to the mash just like wheat malt. The difference is that the unmalted wheat has much larger proteins and a more pronounced impact on foam. This ingredient is commonly used in Belgian ales. I use it at the rate of 0.75 pounds (0.34 kg) per 5-gallon (19 L) batch for an American-style wheat beer that has a beautiful foam. I’ve used the same basic recipe but without the unmalted wheat for a German-style hefeweizen and found that the foam was not as tight or stable as the American-style wheat. Again the main differences in these two beers are the unmalted wheat and the yeast strain.
If I were you I would be looking at the malt. Of course, it goes without saying that if you use inappropriate sanitizers, dirty beer glassware or have flat beer, you will have foam problems. I don’t think you have those problems based on the information you have provided.
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