Trouble with tyramine
There are certain medications that put restrictions on tapped beer because of a potentially bad reaction with tyramine. I’ve read that bottled and canned beer is OK but tapped (kegged) beer is something to watch out for. Correct me if I am wrong, but beer in the keg is the same as beer in a can or bottle (at least from a homebrew standpoint), right? I have seen breweries fill a keg from the same tank they bottle it from - so what gives? I am not a chemist or a doctor, nor do I play one on TV, but I am wondering if Mr. Wizard has any info on this.
San Jose, California
I have answered many questions over the years that deal with medical and health topics. The way I go about answering these questions is reading what I can find about these topics and then reporting what I have read. I always encourage readers to use my answers as background information that may be used to learn more about medical and health issues. Consulting with your family physician is always a good place to start. With that said, I do have some information on tyramine and beer that is interesting.
Tyramine is part of a group of compounds called biogenic amines and is formed when the amino acid tyrosine is decarboxylated. A more familiar biogenic amine is histamine, which is formed when histidine is decarboxylated. Although histamine is most commonly associated with scombroid fish (tuna, jack, blue fish and mackerel, for example) and is not found in beer, its formation is similar to that of tyramine. Tyramine and histamine are formed when certain bacteria metabolize the amino acids tyrosine and histidine. As histamine and scombroid poisoning is associated with the improper storage of fish species rich in histidine, tyramine in beer is primarily associated with the growth of lactic acid bacteria.
Tyramine increases blood pressure if not metabolized by the human body when consumed. Most people do not have a problem consuming foods containing tyramine. However, if you happen to be on a class of drugs called monoamine oxidase inhibitors (MAOI), things are different. MAOI are used to treat depression and anxiety. They also interfere with enzymes called monoamine oxidases that catalyze the oxidation of monoamines. When a person taking a MAOI consumes foods containing tyramine they are at risk of having severe increases in blood pressure that may result in stroke. Clearly this is not a topic to consider lightly.
I want to pause here and cite a few studies. The first paper published on this topic appears to be have been published in 1986 by BJ McCabe in the Journal of the American Dietetic Organization titled, “Dietary tyramine and other pressor amines in MAOI regimens: a review.” McCabe’s paper published a list of foods known to contain tyramine and among them was beer. Other foods known to contain tyramine include aged sausages, sauerkraut, aged cheeses, soy sauce and yeast and yeast extracts, for example marmite. The common trait of all of these food products is the presence, or potential presence, of bacteria that decarboxylate tyrosine. In fact, most of these food products rely on lactic acid bacteria to develop their characteristic flavors. Lactic acid bacteria are no strangers to beer and accordingly some beers test positive for high levels of tyramine. Six milligrams of tyramine is sufficient to elicit a mild reaction in people taking MAOI and 10-25 milligrams can cause a severe reaction.
SA Tailor, et al. published a paper in 1994 entitled, “Hypertensive episode associated with phenelzine and tap beer—a reanalysis of the role of pressor amines in beer.” Tailor’s group analyzed 98 beer samples, 49 packaged and 49 draught samples, and found 4 samples of draught lager that contained tyramine. They concluded from their survey that beer packaged in a bottle or can is acceptable to consume by those taking MAOI, but draught beer should be avoided.
This is where Mr. Wizard has no problem presenting some informed arguments related to this conclusion. If I were to guess the type of beers used in their survey (I have not been able to determine what beers they analyzed for tyramine), I would guess that most, if not all, of the packaged samples were pasteurized. Pasteurization kills spoilage organisms and I would not expect to find significant levels of compounds associated with lactic acid bacteria in pasteurized beer. Even if some level of lactic acid bacteria contamination is present in beer before pasteurization, the level of tyramine in packaged beer is likely to be low. Draught beer is another story, as most breweries do not pasteurize their draught products. Extended storage of kegs will permit more time for lactic acid bacteria to grow. Also, dirty draft lines can be a veritable breeding ground for spoilage organisms, including lactic acid bacteria. If a broader sample of bottled beer was included in the survey I am sure their conclusions would have been very different.
The bottom line is that any type of beer may have elevated levels of tyramine if lactic acid bacteria grow and decarboxylate tyrosine. Many Web sites giving dietary advice to people taking MAOI state that draught beer is off-limits, but bottled and canned beer is acceptable and most of this advice can be traced to conclusions drawn by Tailor’s group. I think this advice should be taken with a grain of salt.
The brewing literature also has references to tyramine in beer and many of these papers cite sour beers, for example lambics, as a beer category known to contain tyramine. It’s the beer that is critical to this discussion, not the package. Lambic is not a style I consider when thinking of draught beer, but I would bet a lot of dough on finding tyramine in bottled lambic. This is an obvious contradiction to the blanket conclusion drawn by Tailor’s group. Similarly, if you have some nasty bottle of contaminated lager you might have a problem.
I think that advice related to food and drug interactions is very conservative by nature. However, you can also be smart about the decision. If you are drinking clean beer, pasteurized or not, the likelihood of consuming tyramine is probably quite low. Still, the most conservative approach is recognizing and accepting that all unpasteurized beer is a possible source of tyramine.
Unfortunately, this advice excludes almost all homebrewed and craft brewed beer. If you know someone taking MAOI that really wants to drink unpasteurized beer and is certain enough that the beer is OK to drink, I strongly suggest that they discuss their understanding of this topic with their physician beforehand to avoid serious problems. I would also suggest better understanding why yeast and yeast extract is on the list of foods to avoid. Very yeasty unfiltered beers may also be a category to consume with caution. Of course another option is to discuss taking a different anti-depression drug with fewer dietary restrictions.
Fighting the foam
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!