Materials for Off-Flavor Workshop

[Pappers_]

In a couple of weeks, a friend (who is also a National BJCP judge) and I are holding an off-flavors in beer workshop.

We're borrowing the basic pedagogy that is used for many sensory training workshops. We'll go over basic info on beer tasting, then taste a somewhat neutral gluten-free commercial beer, practice describing that and use it as a baseline against which we will compare the other samples. For each off-flavor, we will doctor the base beer, distribute them, taste them, describe them, and talk about their sources. Participants will have the base beer in front of them all the time, so they can go back and forth, to help identify the flavor. Sensory thresholds vary person-by-person, participants may find some flavors more difficult to pick out than others.

I've drafted written materials on the off-flavors, which we'll distribute electronically prior to the workshop and in-print at the workshop. They are formatted nicely, etc., but I couldn't get that to show up here and still be readable, so I've just copied and pasted the contents below.

These are still in draft form, if you have any thoughts, think anything is misstated, mistaken, or unclear, let me know. I've purposefully gone away from the 'spec sheet' format and taken an approach that is more prose.

Notes for Off-Flavors in Beer Workshop
Jim Vondracek
October 2017

While I compiled and wrote these notes, none of the information is original with me. I’ve forgotten many of the original sources in the misty depths
of time, but want to highlight three sources that I referenced often while putting this together: The Oxford Companion to Beer (Oliver), Yeast (Zainasheff and White), and the BJCP Study Guide.

Notes on Acetaldehyde


Often referred to as a “green beer”, young or twangy.

Most people perceive acetaldehyde in both taste and aroma as green apples, but sometimes it is perceived as grass or other green vegetation.

Acetaldehyde is a compound produced during fermentation – a yeast derived aroma and flavor. Typically, as the yeast continue to work, it cleans up the beer by reducing the acetaldehyde that it produced to ethanol. In ‘green’ beers, that process has been stopped, interrupted or left incomplete, leaving levels of acetaldehyde above the level at which we can perceive them.
How to avoid making green beer? Yeast management. Pitch healthy and vigorous yeast at a sufficient rate, provide oxygen, maintain the yeast at the right temperature so that it can finish its job, don’t prematurely rack the beer off the yeast. Patience.

Fun Fact: People with a sensitivity for acetaldehyde report that they detect background amounts in Budweiser, perhaps because the addition of beechwood chips cause the yeast to drop out before they have finished reducing the acetaldehyde to ethanol.

Fun Fact #2: Less commonly, acetaldehyde can also be a product of bacterial spoilage. Sanitation.

Notes on Butyric

Oh. My. God.

Should my beer taste and smell like vomit?

Other descriptors sometimes used include rancid, putrid and baby spit-up.

Butyric is formed by bacteria, but in two different ways. Currently, it is normally a post-packaging sanitation issue. While not as common now, it can also be produced by bacterial infection during wort production, prior to fermentation, especially if the ingredients you use are old, moldy, etc. Fresh ingredients solve that problem.

Notes on Diacetyl

Look at the person to your left and then to your right. One of you may not be able to detect diacetyl unless it is at a high level. Diacetyl “blindness” is relatively common.

Diacetyl is a compound responsible for artificial butter (like movie popcorn butter), toffee or butterscotch aromas and flavors. It can also give an impression of slickness in the mouthfeel of a beer.

Like acetaldehyde, it is a product of early fermentation which the yeast will often help to clean up later in the fermentation. Given enough time and vigor, the yeast will absorb the diacetyl and convert it to diol, an innocuous compound. Many lager brewers will build a diacetyl ‘rest’ into their process – where they raise the temperature of their beer towards the end of fermentation, to rouse and invigorate the yeast to complete this task before it falls out. Higher temperatures increase the production of diacetyl but also the process of re-absorbing diacetyl.

Fun Fact: Although diacetyl rests are ‘common wisdom’ among many lager brewers, it may not be necessary if the brewer has managed the yeast and fermentation so that the diacetyl production is kept to a minimum at the very start of fermentation by pitching at a low temperature and a large pitch of healthy and vigorous yeast is used.

Fun Fact #2: Diacetyl isn’t a flaw in all styles, although an excessive amount always is. Low levels of diacetyl are common in English ales and Czech pilsners, for example.

Continued . . .

 

[Pappers_]

Notes on DMS (Dimethyl Sulfide)

Aroma and flavor of cooked vegetables, canned corn, cabbage or celery.

DMS is normally produced by the heat-induced conversion of S-methyl-methionine (SMM), which is an amino acid formed during the germination and kilning of barley as part of the malting process. Most DMS, though, evaporates during a long, open, rolling boil.

Pilsner malt contains up to eight times the amount of SMM as most pale malts, so more DMS is produced in beers where Pilsen is the base malt. If the boil isn’t vigorous or long enough, or the brewing kettle is covered, the DMS won’t dissipate. DMS is a sulfur compound, so it can accentuate the sulfur-like aromas produced by some lager yeasts.

DMS is more common in lagers than in ales. The CO2 produced during an active, vigorous ale fermentation can ‘scrub’ away the DMS. The more restrained fermentation of a lager tends to leave the volatile DMS in place.

Fun Fact: DMS is produced (converted from SMM) throughout the brew day, anywhere heat is applied to the malt. Mashing, boiling, even chilling if you are chilling slowly.

Fun Fact #2: Most people can perceive DMS at low threshold levels – as low as 10 parts per billion.

Notes on Earthy


Terroir taken to the extreme.


Caused by the compound 2-ethyl fenchol. Rarely an issue with beer these days, but when it does occur, it is usually apparent and a disaster for the beer.

As implied in the name, “earthy” usually means a damp soil or freshly dug dirt aroma and flavor.

This serious flaw occurs in beers due to contamination of water and via migration through packaging by 2-ethyl fenchol. 2-ethyl fenchol is produced by microorganisms in water and can be imparted via ground water supplies and then into water for beer production. However, earthy taints are imparted more commonly when finished packaged beer is stored in damp cellars. Microbes in the walls of the cellars produce 2-ethyl fenchol and this chemical migrates through semi-porous packaging into the beer.

Notes on Ethyl Acetate

When Your Beer Has Too Much of a Good Thing

Often, a little ethyl acetate in your beer is a good thing. It is a compound produced by yeast during fermentation and is a common ester – esters are aromatics formed by the reaction between alcohols and acids. In nature, they contribute to the aromas of many varieties of fruits. In beer, they contribute to the overall flavor and aroma of beer, giving a fruity quality even when the beer contains no fruit.

As ethyl acetate intensifies, however, this pleasant aromatic perception changes from fruity to nail polish and solvent. So, in some cases, ethyl acetate enhances beer, but high levels lead to an unpleasant off-flavor.

Some yeast strains produce more ethyl acetate than others, but regardless of the strain, other yeast management and fermentation attributes also impact its intensity – and whether its desirable or a detriment to enjoying the beer. Fermenting at higher temperatures tends to produce more ethyl acetate than at lower temperatures. Using a high pitching rate of yeast, in relation to the beer’s original gravity, will restrain the production of ethyl acetate. Assuring that there is sufficient oxygen available to the yeast prior to fermentation impedes the production of ethyl acetate.

Fun Fact: The application of pressure during fermentation reduces both yeast growth and ester synthesis

Continued . . .

 

[Pappers_]

Notes on Ethyl Hexanoate

Esters Part Deux

Like Ethyl Acetate, Ethyl Hexanoate is a common ester, formed by the reaction between alcohol and acids. Ethyl Hexanoate has an aroma and flavor that reminds people of apples most commonly and sometimes anise.

Like Ethyl Acetate, at low levels, this ester can lend a positive complexity to the appropriate beer style. But at higher levels, it is considered an off-flavor. Unlike Ethyl Acetate, our perception of it doesn’t change at the high concentrations, it just becomes overwhelming and unpleasant.

Some yeast strains produce more ethyl hexanoate than others, but regardless of the strain, other yeast management and fermentation attributes also impact its intensity – and whether its desirable or a detriment to enjoying the beer. Fermenting at higher temperatures tends to produce more ethyl hexanoate than at lower temperatures. Using a high pitching rate of yeast, in relation to the beer’s original gravity, will restrain the production of ethyl acetate. Assuring that there is sufficient oxygen available to the yeast prior to fermentation impedes the production of ethyl hexanoate.

Notes on Geraniol

A Rose by Any Other Name

In the context of beer, Geraniol is usually perceived as a rose like floral aroma, although it can also lend a citrus fruit like aroma. When oxidized, Geraniol smells like geraniums.

Geraniol is an oil compound typically found in hops, particularly American hop varieties. Chemically, it is classified as monoterpenoid alcohol. While hops are the primary way that Geraniol gets into our beers, it is also found in a number of plants that may be used as adjuncts: coriander, lavender, lemon, lime, nutmeg, orange, rose, blueberry and blackberry.

Geraniol is present in Cascade, Citra, Centennial, Chinook, Pacific Hallertau, Southern Cross, Motueka, Aurora, and Styrian Golding hops.

Fun Fact: About 1/3 of us have a much higher sensitivity to Geraniol – with a perception threshold level about 1/20th of the rest of us.

Fun Fact #2: Geraniol is a natural mosquito repellant and is found in some DEET-free products.
 

Notes on Indole

What the Hell?!?!?!?

The aroma and flavor are sometimes described as farmyard or dirty diapers.

This is caused by a bacterial infection – coliform bacteria – the same family to which E. coli belongs. This can be a result of unsanitary water or grains, but is more likely to be caused when improperly cleaned and sanitized equipment becomes the home to coliform bacteria. Keep your stuff clean and sanitized!

Good News: Indole is rare in beers.

Continued . . .

 

[Pappers_]

Notes on Isovaleric Acid

Hoppy Goodness . . . Or Not

Isovaleric acid is natural fatty acid, produced by the oxidation of hop resins. It is pungent (but not rancid) and can be cheese-like or have a sweaty foot odor.

Most commonly, this flaw in a beer is the result of the use of old hops, which have been exposed to the air and oxidized. Using fresh hops, and storing hops in airtight, vacuum sealed packages avoids this issue.

Sometimes, isovaleric acid is not a flaw – in beers intentionally fermented with brettanomyces.

Fun Fact: Isovaleric Acid is naturally occurring in many plants, foot sweat and some cheese.

Notes on Papery (Oxidation)

The aromas and flavors of oxidized beer are most commonly paper or cardboard. These are due to a compound called 2-transnonenal, which has an exceptionally low flavor threshold, so many of us find it easy to perceive even at low levels, and is produced by the oxidation of higher alcohols.

Other flavors may also be produced in oxidized beer – sherry, vinous (wine-like), and stale qualities.

The threat of oxidation may be reduced by minimizing splashing of the hot wort or of the fermented beer while racking or bottling.
Some styles may (not always, but sometimes) be enhanced by an appropriate level of oxidation - generally high in alcohol, dark in color, and malt-focused, like Barleywines, Old Ales and Imperial Stouts.

Fun Fact: Homebrewed beer, and especially bottle conditioned homebrewed beer, seldom show the impact of oxidation due to the presence of yeast in the beer – the yeast delays the staling effects of oxidation. Commercial beers that have been filtered, on the other hand, are more likely to show signs of age and staling more quickly.

Fun Fact #2: Oxidation is usually slow to develop. So, if a brewer introduces significant amount of oxygen to their beer post-fermentation, but the beer is drunk while young, most people won’t detect it.

Notes on Spicy (Phenol)

Phenols are often perceived as black pepper, cloves, smoke, astringent tannin, or medicines such as sore threat sprays.

They can be associated with some yeast strains – Hefeweisen yeasts tend to produce not only banana flavors but clove-like phenols.

Aside from German-style wheat beers and some Belgian-style beers, phenolics are almost always considered an off-flavor.

In addition to yeast-derived causes, phenolic character may be caused by wild bacteria, over crushing of grain, sparging at too high a temperature, sparging with water that is too alkaline, over sparging, chlorine in brewing water or sanitizer residue.

Fun Fact: Chlorine can react with phenols to create chlorophenols, which have a band-aid or rubbery flavor. Unfortunately, the threshold level for most of us is quite low for chlorophenols, so ‘band-aid’ is a somewhat common off-flavor.

Finished!

 

[Brewsader1]

Very cool, I like the format! There may be one issue with your fun fact: "Fun Fact: People with a sensitivity for acetaldehyde report that they detect background amounts in Budweiser, perhaps because the addition of beechwood chips cause the yeast to drop out before they have finished reducing the acetaldehyde to ethanol. " I believe may be incorrect. My understanding is that the beechwood helps create more surface area for the yeast to cling to rather than all flocculating on the bottom. This helps with fermentation and off flavors rather than them floccing out. I may be wrong, sorry if I am!

 

[Northern_Brewer]

Good stuff. Few obvious things occur to me :

Should really be either butyric acid or butyrate, but not butyric on its own. I've only encountered it in wild/sour beers recently.

I wouldn't capitalise ethyl acetate or hexanoate (and the purist in me would at least mention that acetate should really be called ethanoate these days....)

Earthy - should probably mention that some European hops are "meant" to be earthy - initial tasting of 2017 Fuggles suggests that the dull August weather has made this vintage particularly earthy.

Geraniol doesn't taste citrussy - but it gets biotransformed into things like citronellol which do. Bravo is the king of geraniol hops - see this paper for more on both varietal variations and biotransformation products. I'm not sure geraniol really belongs as a fault - particularly in NEIPAs it's considered desirable, it's a key part of the Citra profile.

 

[Pappers_]

Very cool, I like the format! There may be one issue with your fun fact: "Fun Fact: People with a sensitivity for acetaldehyde report that they detect background amounts in Budweiser, perhaps because the addition of beechwood chips cause the yeast to drop out before they have finished reducing the acetaldehyde to ethanol. " I believe may be incorrect. My understanding is that the beechwood helps create more surface area for the yeast to cling to rather than all flocculating on the bottom. This helps with fermentation and off flavors rather than them floccing out. I may be wrong, sorry if I am!

Thanks. I can't remember where I read that, it was a while ago. But adjusting it to make it less specific would probably be wise!

 

[Pappers_]

Good stuff. Few obvious things occur to me :

Should really be either butyric acid or butyrate, but not butyric on its own. I've only encountered it in wild/sour beers recently.

I wouldn't capitalise ethyl acetate or hexanoate (and the purist in me would at least mention that acetate should really be called ethanoate these days....)

Earthy - should probably mention that some European hops are "meant" to be earthy - initial tasting of 2017 Fuggles suggests that the dull August weather has made this vintage particularly earthy.

Geraniol doesn't taste citrussy - but it gets biotransformed into things like citronellol which do. Bravo is the king of geraniol hops - see this paper for more on both varietal variations and biotransformation products. I'm not sure geraniol really belongs as a fault - particularly in NEIPAs it's considered desirable, it's a key part of the Citra profile.

Thanks, appreciate the input and the article!

 

[Pappers_]

The choice of vials wasn't mine - BJCP or Siebel put together the 12 pack of flavoring vials.