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.
Continued . . .
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 . . .
Last edited: