Notes from out sensory training education night held on September 2023. We used Siebel fault kits with tasters blind to the faults at first. Only common beer faults were discussed. Notes feature the talking points of the night including the perception of the faults, how the occur, and how they can be prevented.
Contents:
1. Acetaldehyde – green apple, cut grass
2. Diacetyl – butter, butterscotch
3. D.M.S. – cooked canned corn, cooked vegetables
4. Oxidisation – wet cardboard, old books, stale
5. Chlorophenol – plastic, band-aids
6. Ethyl acetate – solvent-like, nail polish remover
7. Indole – farm, barnyard
8. Isovaleric acid – cheesy, old hops, sweaty socks
9. Butyric acid – putrid, baby vomit
References
NOTE: mg/L = parts per million
㎍/L = parts per billion (parts per 1 thousand million)
1. Acetaldehyde – green apple, cut grass
Active compound Acetaldehyde
Common sources Fermentation product, staling, or contamination
Concentration 45 mg/L
Threshold in beer 10-20 mg/L detected in aroma and flavour
PERCEPTION
- Unripe apples, cut grass, green avocado, latex paint, underripe berries, bready, cidery.
- In higher concentrations perceived as solvent like.
- Produced in fermentation but usually not perceivable unless problems during fermentation, may be noted in unfinished beer.
PRODUCTION
- During fermentation of glucose.
- Second last step in ethanol production.
- May also be caused by oxidation of ethanol.
PREVENTION
- Use a good pitch of healthy fresh yeast and allow fermentation to finish completely.
- Avoid large temperature drops before yeast is finished.
- Acetaldehyde is reabsorbed by yeast at the end of fermentation and during maturation, it is reduced to ethanol (concurrent with diacetyl removal).
- Pressure fermentation may result in more Acetaldehyde produced.
- Hydrostatic pressure (on commercial scale presumably) can produce more Acetaldehyde.
- Avoiding dissolved CO2 during fermentation is recommended as this negatively impacts yeast health.
2. Diacetyl – butter, butterscotch
Active compound 2,3-Butanedione
Common sources Microbial contamination or improper maturation
Concentration 0.6 mg/L
Threshold in beer 0.1-0.2 mg/L detected in aroma, flavour, and mouthfeel
PERCEPTION
- Buttery, butterscotch, butter movie theatre popcorn, toffee
- Changes mouthfeel – has slick mouth coating sensation
- A fault in most styles, though not so unpleasant
- Acceptable only in some styles – small amounts only – some English styles and Premium Pilsner
PRODUCTION
- Produced in normal fermentation as a byproduct of synthesis of amino acid (valine)
- Intermediate product in this reaction is Alpha-acetolactate – diacetyl precursor
- Converted to diacetyl by spontaneous oxidative decarboxylation
- Reaction is faster when hotter (like all reactions),
- Diacetyl returns to the cell and breaks down into acetoin and 2-3 butanediol – flavour threshold for these is very high, therefore undetectable. This pathway is faster at low pH, and only occurs below pH 4.5
- Diacetyl can be produced by bacterial infection, but only certain bacteria produce diacetyl.
PREVENTION
- Healthy yeast can absorb diacetyl 10 times faster.
- Breakdown is also better with higher yeast concentration
- So again, use a good pitch of healthy fresh yeast and allow fermentation to finish completely.
- Premature flocculation can result in high levels of diacetyl
- Avoid large temperature drops before yeast is finished.
- Different yeast strains will leave more or less diacetyl
- Fermenting at low temperatures will reduce the amount of Diacetyl precursors
- Low pH in beer preferable so that diacetyl reaction can finish
- Diacetyl reduction usually by “diacetyl rest” where you increase ferment temp at about ½ of original gravity. Yeast will then absorb the diacetyl into the cell
- You can test for diacetyl and precursor at home to see if you need a rest
- Good handling of beer will prevent exacerbation of diacetyl problem
TESTING
- Heat a beer sample to about 60ºC to force all precursor Alpha-acetolactate to convert to diacetyl (you cannot taste precursor).
- Cool beer and evaluate
- If no diacetyl detected, beer is ready
NOTES
- Hendo commented that diacetyl is often present in beers bottled under less that oxygen free conditions. “You don’t have a diacetyl problem, you have an oxygen problem”.
- Counter-pressure fill, purge bottle, and cap on foam.
3. D.M.S. – cooked canned corn, cooked vegetables
Active compound Dimethyl sulphide
Common sources Wort boiled, wort cooling or contamination
Concentration 200 ㎍/L
Threshold in beer 25-50 ㎍/L detected in aroma, flavour, and mouthfeel
PERCEPTION
- Creamed corn, cooked corn, cooked vegetable, oysters, tomato juice, vegetal, tomato sauce, boiled cabbage or broccoli, seaweed
- In higher concentrations: produces a “slick and mouth-coating sensation” and makes the beer more satiating.
- May be acceptable in small amounts, especially in light coloured lagers
- Super common in a bunch of foods: white wine, milk rum, cooked vegetables, especially asparagus
PRODUCTION
- Dimethyl sulphide, DMS is produced during wort boiling
- The precursor S-methylmethionine, SMM, is present in ALL malted barley.
- SMM is converted into DMS during wort heating
- Research suggests that DMS is generated somewhere around 120°F (49°C) or higher but is not volatile until about 165°F (74°C) and above
- Also produced by some microbial contaminants – certain bacteria and wild yeasts
PREVENTION
- SMM can be controlled in the malting stage, and most modern highly modified malts don’t seem to have much
- You control it boil boiling – a good uncovered boil will allow it to escape
- Suggested to cool wort in less than 2-hours to prevent DMS production from continuing in the hot wort while also not being allowed to evaporate.
- In a vigorous fermentation CO2 will help purge DMS (nitrogen may help)
- Good sanitation will prevent DMS from range of microbes that produce DMS
NOTES
- Brulosophy had a lab analysis done of two beers brewed with 93% german pils malt (Best Malz). One was boiled for 30 mins, the other for 90 mins. In a lab test NO diacetyl was detected in either sample.
- Suggests that the standard homebrew process is sufficient.
- Scott Janish mentioned a study from 1979 that found above the sensory threshold DMS in 7 of 13 commercial beers.
4. Oxidisation (fault kit is trans-2-nonenol)
PERCEPTION
- Stale, papery, wet cardboard, musty, dull, old books
- More noticeable in lighter flavoured beers
- Most often a fault, however well aged, cellared beer may move beyond papery and eventually have sherry-like characteristics. For example Old Ales (17B in BJCP 2021)
PRODUCTION
- Trans-2-nonelnol is a aldehyde responsible for stale beer flavour
- Formed by the oxidation of linoleic acid as beer ages
- Accelerated by heat and oxygen
PREVENTION
- Minimise air pick up in brewing process
- Avoid aerating brewing water, mash, wort, or beer
- Exception: aeration of wort for yeast health
- Transfer beer gently and carefully
- Purge all hoses and vessels of air
- Especially avoid air pick-up during packaging – highest potential for staling
- Keep beer cold
NOTES
- Also impacts many other off flavours.
- Acetaldehyde for example results from oxidation of ethanol
- Diacetyl can be produced after bottling if oxygen is present
- Exposure to oxygen will more rapidly stale hops
5. Chlorophenol
PERCEPTION
- Mouthwash (not minty), chemical, antiseptic, hospital-like, chlorine, plastic, iodine, band-aid
- Common fault for newer brewers
PRODUCTION
- Chlorophenol taint is caused by the introduction of cleaning chemicals entering beverage raw materials or the final product where pipes or vessels are not fully rinsed.
- Water supplies are treated with chlorine or chloramines then there is a high risk that it will end up in the end product.
PREVENTION
- Treat brewing water brah
- Campdem tablets ½-1 tab per 20L batch / potassium metabisulfite or sodium metabisulfite added before mash. Only about 150mg of those required.
- Filter slowly with good carbon filter
6. Ethyl acetate – solvent-like, nail polish remover
Active compound Ethyl Acetate
Common sources Wort composition and yeast growth
Concentration 60 mg/L
Threshold in beer 20-40 mg/L detected in in aroma and flavour
PERCEPTION
- One of the most common esters in beer
- At higher concentrations: Solvent like, nail polish remover, acetone, model glue, paint thinner
- At low concentrations it contributes to a fruity flavour profile in beer
- Part of an overall ester profile of “fruity characteristics”
- Common in most ales styles (levels vary) not common in lagers
- Some beers styles defined by their ester profiles, eg. Isoamly acetate – hefeweizen
PRODUCTION
- Produced by yeast during fermentation
- Strongly dependant on yeast strain, and fermentation profile
- This also applies to common esters ethyl acetate, ethyl hexanoate, and isoamyl acetate
- These are esters are produced by the reaction of an acid with an alcohol: formation is catalysed by enzyme Acyl Alcohol Transferase (AAT)
PREVENTION
- Ester level is dependant on levels of the acids and alcohols present (substrates) but enzyme concentration and activity is the controlling factor
- INCREASED by: poor wort oxygenation, high ferment temperature, low pitch rate, high gravity wort, higher glucose concentration
- So treat with good wort oxygenation, cooler ferment, healthy pitch, and potentially reducing adjuncts
7. Indole – farm, barnyard
Active compound Indole
Common sources Bacterial infection during fermentation
Concentration 0.55 mg/L
Threshold in beer 10-20 µg/L detected in aroma and flavour
PERCEPTION
- Faecal, barnyard, pig-like, coliform
- Definitely negative
PRODUCTION
- Produced by bacterial contamination especially enteric bacteria such as Escherichia coli and others.
- These bacteria are gram negative and pH and alcohol sensitive
- Therefore they can only grow in wort and in the early stages of fermentation
PREVENTION
- Breweries with this problem have a fundamental cleaning and sanitation problem
- Clean and sanitise anything that comes into contact with wort and beer
NOTES
- Not very common, but when present is very unpleasant! Poo!
8. Isovaleric acid – cheesy, old hops, sweaty socks
Active compound Isovaleric Acid
Common sources Use of old, degraded hops
Concentration 3 mg/L
Threshold in beer 1 mg/L detected in aroma and flavour
PERCEPTION
- Cheesy, sweaty socks, blue cheese, rancid, putrid
- Old hops
PRODUCTION
- Formed in old or improperly stored hops
- Alpha acids are oxidised to isovaleric acid and other acids
- Will reach a peak cheesiness, then decrease over time
- So it exists in beer made with old hops
- Belgian brewers can age hops for several year – lose ALL aroma including cheesy aroma, but still act to inhibit bacteria in finished beer
PREVENTION
- Use freshest hops available, especially for late additions
- Properly store hops!
- Keep very cold
- Keep vacuum sealed
- Buy from a reputable source with fast delivery
NOTES
- “More shoey than pooey” (Tony van der Linden, circa 2018).
9. Butyric acid – putrid, baby vomit
Active compound Butyric Acid
Common sources Bacterial contamination
Concentration 7.5 mg/L
Threshold in beer 3 mg/L detected in aroma and flavour (flavour threshold is a little higher than aroma)
PERCEPTION
- Vomit baby vomit, putrid, rancid cheese, parmesan
- Obvious flavour defect
PRODUCTION
- May happen if mash goes on too long or wort is held warm before fermentation, for example in kettle sours
- Caused by microbial contamination by Clostridium butyricum which will grow in wort that is held below 45ºC for extended period of time
- Can also grow in spent grain
- Pectinatus and Megasphaera can produce butyric acids, and other acids, in kettle souring
PREVENTION
- Avoid holding wort warm and open for an extended period
- Cool and pitch fresh healthy yeast ASAP
- Holding in sealed sanitised cube is ok – swelling would indicate otherwise
- Prevent in kettle sours by cleaning and sanitising anything than contacts wort, careful monitoring of mash temperature, and sensory testing for off aromas
NOTES
- Should be rare in normal beer processes, unless there are hold ups
References
Beer Judge Certification Program. (accessed 2023). Beer Faults. BJCP.org https://www.bjcp.org/education-training/education-resources/beer-faults/
Carpenter, D. (2014) Off-flavour of the week: DMS. Beer and Brewing. https://beerandbrewing.com/off-flavor-of-the-week-dms/
Janish, S. (2016). How to Prevent DMS in Beer. Scott Janish.com. http://scottjanish.com/how-to-prevent-dms-in-beer/
Schott, M. (2015). Update: Lab data on pils malt boil length exbeeriment. Brulosophy. https://brulosophy.com/2015/10/08/update-lab-data-on-pils-malt-boil-length-exbeeriment/
Siebel Institute of Technology. (accessed 2023). Individual compound learning videos. https://shop.siebelinstitute.com/sensory-training-kits-individualCompounds
White Labs Technical Team. (2022). Compound spotlight: Diacetyl. White Labs. https://www.whitelabs.com/news-update-detail?id=54&type=NEWS#:~:text=The%20chemical%20reaction%20is%20caused,be%20affected%20by%20insufficient%20nutrients.