http://www.singingboysbrewing.com/blog/off-flavors-in-beer-materials-for-off-flavors-workshop
These are materials I'm using for an off-flavor workshop in October. You can follow the link above and see it in its formatted glory or I've copied and pasted the plain text below. Any responses, critiques and suggestions are welcome!
===================================================
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.
There are no 'fun' facts about butyric . . .
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.
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
These are materials I'm using for an off-flavor workshop in October. You can follow the link above and see it in its formatted glory or I've copied and pasted the plain text below. Any responses, critiques and suggestions are welcome!
===================================================
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.
There are no 'fun' facts about butyric . . .
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.
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
