Sensory Training 2023: Fault Notes

September 29, 2023 / Comments (0)

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.

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