Most if not all homebrewers have brewed a beer at one time or another that has just not come out right. I know I have made a dumper or two, but that is all part of the learning process. When tasting your beer and finding that odd taste, weird aroma, or unique mouthfeel it is helpful to understand what you are sensing, what causes the flaw, and how to correct it.

A great place to start when trying to identify a flaw is the BJCP score sheet which can be found on the BJCP website. The score sheet lists a descriptor along with a general overview of the perceived quality. Not all are necessarily a flaw in the right volume. For example, a small amount of Diacetyl is acceptable in some English beers, while phenolics are ok in some Belgian styles. If the judge finds a quality that is deemed a flaw they should generally provide feedback on it and how to correct the issue in the future. They may say the beers exhibits excessive fruity esters, ensure proper fermentation temperature control or keep the fermentation temperature from rising above the recommended range for the yeast.

Over the next several articles I will walk through many of the most common and some uncommon flaws that a homebrewer and even some commercial brewers experience in their beers. I’ll touch on how it is perceived to the drinker, what causes the flaw, and how to correct the issue. If you have some of these flaws, don’t fret, it happens to nearly every brewer. I’ve even had commercial beers from micro breweries that display off flavors.

One last note before we get started, if you believe something is wrong with your beer but you cannot put your finger on it have a friend try it and describe it. You may be surprised that they are able to pick out something that guides you to one of these descriptors. If that doesn’t work, try your local homebrew shop such as Love2Brew or your local homebrew club. Of course you can always submit your beers to a competition and get a BJCP judge to let you know what the problem may be and how to correct it.

Acetaldehyde

Have you ever had a beer that smelled and tasted cidery? The last beer I made, the yeast starter had a strong aroma of apple. When I tasted the spent wort it tasted much more like cider than beer (always taste your starter to see if anything is wrong). This is most likely acetaldehyde, a cidery or green apple aroma and flavor. This is a fermentation flaw that can be caused by a number of things including a high fermentation temperature, over pitching, and poor wort aeration.

The good news is this is fixable in an existing beer and preventable in a new beer. If you’ve found this in your beer it is possible to correct this if it is still in the fermentor. The yeast will clean it up, therefore it is best to leave the beer in the fermentor and rouse the yeast back up. If you’ve racked to secondary or are already in the lagering stage, raise the temperature back up some to keep the yeast working.

Before you toss the yeast in, there are several things you can do to ensure a healthy fermentation and prevent acetaldehyde to begin with. First, start by pitching the proper amount of yeast for the gravity and volume of your beer. Go to MrMalty.com and use the yeast pitching rate calculator to get the correct amount. Second, aerate in some fashion. Pure oxygen is ideal here, but if that is not possible a filtered aquarium pump or even sloshing the wort around will do. Lastly, ensure you have a proper fermentation temperature for the yeast you are using and keep that temperature under control. Use a fermentation chamber or swamp cooler to make this happen. Check with the yeast manufacturer for the proper temperature range and stay away from the top end of that range.

Alcoholic

How can this be a flaw in a beer, right!?! Well, when a beer that has too much ethanol and fusel alcohol in it, it will come through in all facets of the beer, particularly with the fusel alcohols. Recall that burning or hotness that you get when you drink some cheap tequila or vodka. This can come through in a beer as well. While this is on the extreme end, in all beers a harsh alcohol note is not ideal. That is not to say alcohol can’t come across but it shouldn’t be harsh or hot.

If you have this in your beer post fermentation there isn’t a whole lot you can do about it. You could consider blending it with another beer to balance it out and reduce the alcohol notes but that would be an extreme solution. To prevent this in future beers you can start with fermentation temperature control (a common theme for many flaws). If you let the beer get too warm during fermentation you are more likely to get the fusel alcohols you don’t want. Even try to pitch the yeast at the proper temperature. If you pitch warm the yeast can form the alcohols early and never recover. The higher the gravity of the beer the more likely fusel alcohols are to form. Additionally, if you add simple sugars like table sugar you are more likely you are to get these unwanted alcohols. Keep your high gravity beers under proper temperature control. This is a delicate balance because if you go too low the beer will not finish out and you will have too much sugar left. Try targeting 66-68 F and keeping it there. Near the end of fermentation if your gravity is too high let it ramp up a couple of degrees.

Astringent

Astringent can be a tough flaw. It can be a process flaw or a recipe flaw. I’ve heard this flaw described as like sucking on tea bag. If you want to replicate this you can use grape tannin mixed in with a light lager. In a finished beer you are out of luck. Once astringency is present there isn’t a whole lot you can do about it short of blending which will only reduce it (and ruin a perfectly good beer). Preventing it is the only way to go.

From the process side of the beer, astringency can be caused by over sparging, sparging at high temperature, and sparging with water with a ph above 6.0. To prevent astringency stop sparging when the runnings get down to to 1.010, do not sparge with water that is more than 170F and ensure your sparge water is below 6.0 ph. You will need the right tools to ensure these things happen. I recommend a calibrated thermometer, ph meter, and refractometer. However, ph strips and a hydrometer will work as well.

On the recipe side, over hopping and the addition of certain spices can contribute to astringency. This will fade with time so just let the beer sit. when formulating your recipe ensure it is balanced between hops and malt while controlling spice levels. Check the appropriate OG/IBU ratio for specific styles and use the BJCP guidelines as a starting point. Lastly, some wild yeasts can contribute to astringency, therefore as always ensure your diligence in sanitization.

Next week I’ll continue discussing more flaws and their prevention/correction.