May 28, 2015 by fhsteinbart
Last week we discussed the three major flaws in beer that are most commonly found. They represent the majority, but not all the off flavors are all that well known as the big three (diacetyl, acetaldehyde, and dimethylsulfide) are. The next off flavors we will examine are flavors of oxidation, yeast autolysis, and light struck.
A lot of people come to me with beers that when I taste them I get the flavor almost immediately, namely that of oxidation. This flavor when done properly tastes like port or sherry wine like, but when done too quickly, or from thermal stress (storing at too high a temperature) results in more cardboard, papery, or musty like flavors. The best cure is prevention, that is to say keep your beer cool or even cold, and limit the ingress and egress of gasses by proper closure procedures. Oxidation, over a long time period of three years or so will yield those more desirable notes of sherry, port, or even tobacco.
The second off flavor of this week’s topic is one that I personally detest: yeast autolysis. I once went on a tour of a nearby soy sauce plant here in Oregon, and the smell of yeast autolysis filled the entire plant with its meaty, brothy, vegetal aroma. While finding this flavor in soy sauce is wonderful, finding it in your beer is not so much so in my humble opinion. The primary cause is from dead yeast, hence the name yeast autolysis, which literally means yeast cleaving. this causes the insides of the yeast to intermix with the medium it is found in, which in this case is beer, and the result is just plain nasty. The only prevention is to rack the beer off of the primary yeast cake after fermentation has resorbed all the other off flavors like diacetyl, and acetaldehyde. It does take quite a bit of time to get to the stage of autolysis, but you need sickly, unhealthy, dying yeast to accomplish this task. This is why I always tell people to use as much healthy, active yeast as is practical to use in a fermentation.
The third, and final off flavor of this week’s discussion is light struck (aka skunky), which UV2 light interacts with isohumolone, and produces methyl mercaptan, which is in the same family as the odorous compounds as found in a skunk’s scent glands. Perhaps this is why we say that a beer is “skunked” instead of saying “light stricken”, the more correct ascertation. The only way to avoid it is to use proper packaging techniques that block UV2 light, and keep the beer away from strong light sources even when imbibing. This is why beers in brown bottles taste better, while green and clear bottles do not. Of course kegging avoids all those issues altogether. Miller is the only beer where this is not a problem as they do not use actual hops in making their beer, but preisomerized extracts instead. Perhaps craft brewers should investigate the use of preisomerized extracts in their beers not only for the prevention of being light struck while in trade conditions, but also for more consistent results in bitterness, flavor, and aroma.
Next week we will discuss another three off flavors found in beer. Also, we’ll discuss the prevention, and possibly any cures for that particular condition. From my own personal experience, the only way to reduce, or eliminate the flaw without destroying the original beer is to either blend with another beer of the same style without that defect, or to add another stronger flavor to try and cover up the original defect of that beer. This is where I believe the first fruit beers to have been made were created for, namely to cover up a noticeable, but fixable flavor defect.