Ask Mr. Wizard

How does silicone affect beer foam?


Michael Starr • Cincinnati, Ohio asks,

I am currently a graduate student studying materials science (polymer focus) and a teaching assistant for a professor who is considered an expert on the subject of silicones. Recently he informed our students that some form of silicon is used in the brewing of beer to reduce the amount of foam. I’m assuming this is referring to the fermentation process, but I may be wrong. I see the scientific reasoning behind this idea but my question is are there commercial brewers or homebrewers who actually use silicon during any part of their brewing? And if so, how and what type of effects could this have on the flavor and body of the final product, if any?



The professor you are working for is correct to state that some brewers use anti-foams and it is also true that these compounds are silicon-based. Dimethylpolysiloxane, in the form of a water-based emulsion, is one type of anti-foam sold commercially.

The reasons that brewers would want to reduce foaming are pretty simple to understand. Foaming during wort boiling is one of the contributors affecting hop utilization. When foaming is reduced in the kettle, hop utilization tends to increase. This is because iso-alpha acids and alpha acids partition into foam, and when the foam sticks high on the kettle wall there is a loss of these compounds. Also, foaming during boiling can be dangerous if a kettle over-boils. Anti-foams used in the brewhouse are typically added as the kettle is heated so that the anti-foam mixes with the beer, and they work by decreasing wort surface tension.

A more common application of anti-foams is during fermentation. Foaming during fermentation is an expensive phenomenon and commercial brewers regularly use fermentation vessels with considerable headspace above the beer level to accommodate foam. One way to brew more beer is to fill the fermenters to a higher level. If this is done without the aid of anti-foam, the fermenter will blow foam and beer from the top of the tank. This makes a mess and results in beer loss. Add a little anti-foam, usually around one milliliter of anti-foam per 20 liters of beer, and this problem largely goes away.

Foam reduction during fermentation does more than simply allowing the fermenter to be filled to a higher level without causing a messy blow over. Hop utilization is increased, the loss of foam-positive proteins is reduced and the loss of trub to surfaces is decreased. Because of these factors, if anti-foams are used, the brewer will probably want to decrease the hopping rate to balance the increase in utilization that is expected.

The reported reduction in foam-positive proteins is exciting for foam lovers. Contrary to what one may assume about using anti-foams, they are known to actually improve the foam in the finished beer. Obviously the anti-foam must be removed from the beer before packaging and settling and filtration are two methods used to remove the anti-foam. Commercial brewers usually filter their beers, but anti-foam removal can be performed without requiring longer aging times. At home I would follow the manufacturers recommendations with respect to gravity removal and not try to shave days off the settling time specified.

This is all sounding pretty good. No foam blowing out of the fermenter, improved hop utilization and improved foam stability! It makes you wonder why all brewers do not use anti-foams. I think one potential downside to anti-foams is an increase in so-called braun hefe trub in the fermenting beer. This is the darkly colored schmoo that sticks to the wall of the fermenter when foam is allowed to form during fermentation. When the foam collapses as fermentation wanes this stuff is partially removed because it sticks to the side of the tank.

Some brewers remove braun hefe from the tops of fermenters by skimming open tanks and some brewers encourage some foam to flow from the tops of closed tanks into special foam chambers designed to remove braun hefe from beer. Braun hefe removal is done to produce a mellower flavor in the finished beer. To my knowledge, the only real downside to beer flavor when using anti-foams could be an increase in harsh flavors associated with braun hefe.

Some commercial brewers are hesitant to use brewing aids because of the perception the beer-drinking public may have. However, brewing aids are not considered ingredients because they do not survive into the finished beer. Silica gels are widely used to stabilize beer against chill haze and these compounds, like silicon anti-foams, are completely removed from beer. Even the restrictive Rheinheitsgbot does not prevent German brewers from using silica gels because they are not ingredients.

The concern that some brewers have is that labeling rules can always be changed. If a new labeling law required the brewer to list brewing ingredients and aids this would be bad for the brewer who must list big words on their labels. Terms like silica gel, polyvinylpyrrolidone (PVPP) and dimethylpolysiloxone sound pretty scary to the average beer consumer. So that’s my take on anti-foams!

Response by Ashton Lewis.