• Mmm…bananas!
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Post Title: Bad Beer

Post Date: October 28, 2013

Have you ever had a craft beer that didn’t taste right? Maybe it’s all the years I worked in a lab with bacteria and yeast, but I can smell and taste contamination in a beer from a mile away. It’s my gift, though I don’t get to use it all that often, since it is very rare that a brewery will put out a contaminated beer. I did try and use my gift on my husband once after I took a sip from his pint glass, but he did not believe my warnings; ever since that time, he has me sip the beer before he will even try it.

In our Sensory Evaluation class I am learning to hone my sense of taste to pick out specific flavors in beers. Whether a flavor is desirable or undesirable is subjective; oftentimes, flavors labeled “undesirable” actually are — in small quantities — part of a beer’s flavor and, in some cases, may even help define a style.

Most Hefeweizens have detectable amounts of isoamyl acetate that gives them the flavor of banana. The Great American Beer Festival Style Guide’s description of a Hefeweizen notes that “The aroma of a German Hefeweizen is decidedly fruity and phenolic. The phenolic characteristics are often described as clove-like, nutmeg-like, mildly smoke-like or even vanilla-like.... The flavor of a Weissbier with yeast is decidedly fruity and phenolic. The phenolic characteristics are often described as clove-like, nutmeg-like, mildly smoke-like, or even vanilla-like. Banana-like ester flavor should be present at low to medium-high levels.”

In class, we were able to try beers that had been spiked with undesirable flavors — some more undesirable than others, such as rotten eggs — to help train our palates and noses.

Here are three common “undesirable” flavors that can be found in beer:

Isoamyl acetate (banana flavor)

Isoamyl acetate is an ester by-product of yeast metabolism and is present in almost all beers. Higher fermentation temperatures increase the amount of isoamyl acetate. Once it is present in your beer it can’t be removed post primary fermentation. Most people can’t taste it below 1.6ppm. The taste and smell can be found in anything that has artificial banana flavor. For me, it evokes memories of banana Chap Stick; others in the class say it reminds them of Runts or Circus Peanuts, neither of which I have tried.

Try eating some Runts and later see if you can pick out the banana flavor in your favorite hefeweizen.

Dimethyl Sulfide (creamed corn, cabbage)

Dimethyl sulfide (DMS) is a product of the precursor SMM from malt and is removed by vaporization during boiling. DMS often occurs if beer is not boiled rigorously enough or is not cooled down quickly enough after boiling (for example, if the beer is left in the whirlpool too long before being chilled). Poor ventilation of the boiling kettle — that allows for condensation to drip back down into the beer — causes the bacterial contamination that produces DMS.

Our example of a beer that had a lot of DMS was a bottle of Rolling Rock. I suggest sniffing a can of creamed corn or a can of black olives (also known to have a lot of DMS) and then trying a Rolling Rock to see if you can pick out the flavor of DMS.

3-MBT (light struck/skunk)

When isohumulones found in the alpha acids in hops are exposed to light they form 3-MBT. Many beers are stored in dark glass bottles to prevent this from happening; brewers wanting to use lighter glass bottles can prevent this from happening by using already reduced hop extracts. Many people do not mind this flavor because it reminds them of drinking a beer on the beach. It is also important to note that this reaction happens quickly, so if you have a beer in the sun, find some shade to enjoy it.

To taste 3-MBT leave a Corona bottle in the sun for an hour (you can leave the cap on).

We also got to taste beers that had been spiked with clove phenols, moldy water, and sulfur. I am pleased to say my stomach survived it all and my palate emerged forever transformed.

Happy tasting!

Title: UCSD’s Brewing Program | Address:

Author: Sarah G | From: North Park | Blogging since: September 2013

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