Beer Flaws Sensory Evaluation

This document contains ideas for presenting and for getting the most from attending a Sensory Evaluation of flavor flaws commonly found in beer – both homebrew and commercial. This is available as a Microsoft Word file at IndianaBeer.com. Please feel free to make copies or modify it as you wish.

These "tastings" are small and incomplete sessions based on the full Sensory Analysis Seminar course presented by Siebel Institute of Technology on a regular basis (SiebelInstitute.com). We must first thank Siebel for developing this course and point out that this tasting is only a sample, not a substitute for this professional course.

The chemicals used in this evaluation come from Sigma Aldrich’s Beverage Kit W600016 (SigmaAldrich.com). There are 24 small, stinky vials in this kit which are detailed later. Less than one drop of each of these chemicals applied to a 32oz Budmillercoors gives plenty of aroma. These 1 to 2 oz samples are NOT meant to be sipped; most aren’t dangerous but tongues aren’t necessarily going to appreciate the experience. A few are labeled on the bottle "toxic – easily absorbed through skin".

A coffee-stirrer straw dipped into the vial will extract a small drop. We then tapped the straw inside the bottle to get the rest of the juices. A few vials contain powder and we put in the equivalent of maybe 5 grains of salt.

Note all samples except the DMS and vinegar were prepared from this kit using less than a drop in a big screw-top bottle of big-time beer. If you attempt this at home, do it outside! The DMS sample was ingeniously prepared by adding some juice from a can of corn to the beer.

All About Beer (Vol 22 # 5) had an article on how to doctor beer for a tasting such as this. It’s available online at AllAboutBeer.com.

First, we’re going to investigate a little bit about how we perceive taste. We’re going to use Brach’s Spice Drops.

1. Hold your nose.
2. Chew a little bit on a gumdrop.
3. Note that you can perceive the sweetness but can’t tell the flavor.
4. Let go of your nose.
5. Note that you can now taste the gumdrop.

There are special taste buds on the tongue that sense

• Sour – on the sides of the tongue. Acids (ie Geuze)
• Bitter – on the back of the tongue. Alkaloids (ie IPA)
• Sweet – on the tip of the tongue. Sugars (ie Milk Stout)
• Salty – on the tip of the tongue. Salts (old timers salted their beer)

And some people say there’s a fifth taste – Umani – Glutamates (including MSG).

Everything else comes through the nose.

* Labeled as toxic and easily absorbed through skin. It’s not suggested that you drink these.

Banana – Isoamyl acetate

Produced by certain strains of yeast typically associated with Germain Weizens.

Band Aid – Phenol – Carbolic acid

Caused by bad sanitation and bacterial infection. Sanitizers containing chlorine bleach will multiply these bad aromas. Carbon filtering will help. Clean or replace all tubing.

Butterscotch – Diacetyl - 2,3-butanedione

A natural byproduct of fermentation. To eliminate excess diacetyl, a "diacetyl rest" is sometimes used. Leave the beer in the fermenter for 2-3 days after the fermentation seems complete and the yeast will reabsorb the diacetyl. Warming the fermentation of lagers to near 65ºF near the end will also facilitate this.

A test for excess diacetyl is to refrigerate a sample and heat another sample to 140ºF for an hour. If the heated sample tastes more buttery than it’s cold counterpart the yeast hasn’t done its job yet.

Pediococcus and lactobacillus bacteria also produce diacetyl so sanitation problems often are the cause.

Diacetyl can be removed with a diatomaceous earth filter.

Canned Corn – Dimethyl Sulfide (DMS)

DMS is produced while the wort is hot but disappears into the air during boiling. If the wort is cooled slowly more DMS is produced or dissolved back into the liquid. Make sure there is sufficient ventilation in the kettle during and after boiling.

A more intense, rancid intensity of DMS can come from bacterial infection. This is caused by poor sanitation and tastes more like cooked cabbage. This specific bacteria grows well in plate heat exchangers.

Cardboard - Oxidation - trans-2-nonenal

Often caused by improper bottling or capping, allowing excess oxidation to contact the beer. Sulfur Dioxide can prevent oxidation. Light will also promote this taste.

Cat Urine – Sweat socks – Isovaleric acid

Most often the result of old, stale hops.

Cheese – Butyric acid

Pasteur’s investigations in the 1850’s found butyric acid is formed by anaerobic microorganisms that are inhibited by oxygen. It was he who invented the word anaerobic. "Fermentation by yeast appears, therefore, to be essentially connected with the property possessed by this minute cellular plant of performing its respiratory functions, somehow or other, with the oxygen existing combined in sugar."

In short, bacteria in the wort forms this aroma and oxygen introduction prior to fermentation will help keep it at bay.

Clove – Eugenol

Eugenol is found in clove oil and isn’t itself a byproduct of beer production. Clove flavor in beer is normally from 4-vinyl-guaiacol which is produced by German Weizen yeast such as Wyeast 3056 or White Labs WLP380. Can also be used by bacteria / poor sanitation and an acid wash of yeast is recommended.

Estery - Apple – Ethyl Hexanoate

Ethyl Hexanoate can be found in all beers as a byproduct of fermentation. Stuck yeast can form this chemical in higher concentrations. Fermentation at too high a temperature will also cause this as a problem as the yeast cannot mature correctly. More common in lagers.

Goat – Hexanoic acid

Lactobacillus or Pediococcus bacterial infection due to bad sanitation..

Oily – Octanoic acid

Yeast residue is the normal cause of this aroma which is normally at very low levels. Pasteurization destroys this chemical but it can pass through cold filtering.

Pear – Heptyl Acetate

This is a tough flavor to get into beer and is usually not considered a flaw (Fuller’s IPA for instance using Kent Goldings hops).

Intense Acetaldehyde chemicals can give apple/pear Jolly Rancher flavor. It comes from normal yeast activity or from bacterial infection.

Skunk – Mercaptan

"Photochemical reactions of isomerized hop compounds". Actually it is blue and ultraviolet light that reacts with oils from hops to skunk beer with 3-methyl-2-butene-1-thiol (MBT). Sunlight and fluorescent lights have lots of this bad light. Brown glass bottles screen out the blue wavelengths.

Smoky - 4-Ethylguaiacol

This chemical is formed from ferulic acid in the roasting process of malt.

Smoky Bacon – 2,6-Dimethoxyphenol

Not normally found in beer. Included here just because it’s such a good aroma and it was included in the Sigma-Aldrich kit.

Solvent - Acetone

Usually associated with fermentation at too high a temperature. Corn in the mash will also produce acetone aromas.

Sourness – Lactic Acid

Good sourness such as in a Lambic is one thing. Bad sourness with burning in the throat or a vinegar flavor is another. The problem is usually a bacterial infection. Often a lactobacillus that is present in old grain is the cause when sparging is done under 170ºF. Infection may also come from sugars, acids, and yeast. Wort exposed to air can also pick up lactobacillus.

Vinegar – Acetic Acid

See Sourness, above.

The European Brewery Convention and the Master Brewers Association of the Americas have adopted a Beer Flavor Wheel developed by Morten Meilgaard in the 1970s. It was published in Brewing Techniques (Vol 5 #6) and is available online at BrewingTechniques.com. Aromas included in that flavor wheel are:

32oz screwtop Miller Lites are our choice to use as a base beer. It has more malt characteristic than Coors or Bud. Plus, Miller uses a GMA hop strain that is resistant to skunking due to UV light.

Dosages we use range from miniscule to 3 drops.

1. Dip a toothpick in the vial and drop it into the beer. This wets only ¼ inch of the toothpick
2. Using a coffee stir-straw, pipette a drop by dipping and closing the top with a finger. Then shake off the excess in the inside of the bottle. Discard the straw, of course. Reuse will contaminate the chemicals.
3. Due the same as 2) but repeat two or more times to get two or more drops.
4. Some chemicals are powder. Use the amount noted below.

* Labeled as toxic and easily absorbed through skin. Take care.

©2005, Bob Ostrander. Please feel free to make copies of this document or modify it as you wish.