Common Off flavours in beer - PowerPoint Presentation

Common Off flavours in beer Sensory training

Sponsored by Newstead Brewing Co.

Siebel Institute Sensory Kit12 “off-flavour” vialsEach is mixed into 1L of beerSamples are on the extreme end of the flavour threshold

Sample #1 What is wrong with this beer?

AcetaldehydePerceived AsBruised apples, green apples, cut grass, squash-like, latex paint, rough, jolly rancher. Often sweet apple esters and sourness is mistaken for this off-flavour.Flavour Threshold - 10-20 mg/lSample - 45 mg/lImportanceIt is present in all beers at some level. It is part of the flavour profile of certain styles, such as American lagers and Biere de Garde.Effect of AgingGenerally will increase with age.Caused ByIt is produced by yeast during fermentation as a precursor to ethanol. Can also be caused by oxidation, where too much O2 exists in packaged beer, it can change ethanols back to acetaldehyde.

AcetaldehydeHow To Avoid/ControlPitch enough healthy yeast. Use proper fermentation temperature.Avoid aeration after fermentation has begun.With lagers, allow fermentation to finish at a slightly higher temperature.Condition at a slightly warmer temperature.Minimize O2 introduction during bottling.Use a diacetyl rest.Wait a couple days after fermentation is complete before racking off of yeast.Use sound sanitation practices.Commercial ExampleBudweiser contains low levels of acetaldehyde as part of its flavour profile.

Sample #2 What is wrong with this beer?

Butyric AcidPerceived AsRancidity, Baby vomit, cheesy, putrid, spoiled milk or butter.Flavour Threshold - 2-3mg/lSample - 7.5 mg/lImportanceAlways considered an off flavour in beer.Effect of AgingCan increase if packaged beer has bacterial contamination.Caused ByBacterial Infection of sugar syrups; or during wort production, sour mashes in aerobic conditions, or after packaging. Flavor becomes more prominent with a lowering of pH.

Butyric AcidHow To Avoid/ControlSanitation is key to avoiding this horrid off flavour.Smell and taste syrups before using them to ensure they are not contaminated.Do not expose sour mashes to outside air and keep them above 32°C.

Sample #3 What is wrong with this beer?

DiacetylPerceived AsButtery, buttermilk, milky, oily. Lower levels can appear almost Caramel-like; at higher levels Buttery or butterscotch — think movie popcorn. It can cause a milky or slick sensation on the palate. Easier to detect in light lagers, any added complexity in a beer such as darker more robust flavours will make detection more difficult.Flavour Threshold - 0.1-0.2 mg/lSample - 0.6 mg/lImportanceIt is usually considered an off flavour, but is appropriate at low levels in some styles, including English Bitters, Scotch Ales, Dry Stouts, and Czech Pilsner to name a few.Effect of AgingDiacetyl can become more pronounced over time in packaged beer that has the precursor of diacetyl, alpha acetolactate. As the alpha acetolactate breaks down it forms diacetyl. Heat accelerates this breakdown.Caused ByIt is produced by all yeast during fermentation, but is usually reabsorbed by the yeast cells. Non-reabsorption or over production is caused by feeble or short boiling, low temperatures during fermentation, mutated yeast, or racking too soon. It can also be formed by bacteria contamination.

DiacetylHow To Avoid/ControlAlways boil vigorously for the appropriate amount of time.Aerate your fermentation well when you cast your yeast. Avoid oxygenating the wort further once fermentation has begun.Up your temperature slightly as you near the end of fermentation. This helps the yeast reabsorb diacetyl.Don’t be too quick to rack your young beer off the yeast. Ensure the little guys are done doing their work before you move your beer off of them.Commercial ExamplePilsner Urquell is a commercial example that has diacetyl as part of its flavor profile.

Sample #4 What is wrong with this beer?

Dimethyl Sulfide - DMSPerceived AsSweetcorn, Creamed Corn, Cabbage, Canned/Cooked Vegetables, Oysters Sea Vegetables, Tomato SauceFlavour Threshold - 0.025 mg/lSample - 0.2 mg/lImportanceConsidered an off flavour in most beer, but can play some role in the flavour profile of some pale lagers, German and American pilsners, and cream ales.Effect of AgingLikely will decrease with age.Caused ByDMS comes from a sulfur-based organic compound (S-methyl methionine, or SMM) produced when grain germinates during the malting process. Six row lager malts and Pilsner malts have the highest levels of this compound. As do some adjunct grains such as corn. SMM (S-Methyl Methionine) changes to DMS during the boil. It can also come from wild yeast or bacterial contamination during fermentation.

Dimethyl Sulfide - DMSHow To Avoid/ControlReduce use of pilsner malts, lager malts, and corn adjuncts.Higher moisture content in malt increases the SMM (S-Methyl Methionine), so make sure you store your malt in a dry, cool place.Over-sparging can increase DMS.DMS is a volatile compound and the easiest way to get rid of it is to drive it off with a vigorous boil. Always use a big enough kettle to allow for an energetic boil without having to worry about boil over. And always leave the lid off!Ensure your vigorous boil is long enough. Boil for at least 60 minutes and, if using lager or pilsner malt, consider upping it to 90 minutes.Also try your best to crash cool your boiled wort as quickly as possible. DMS is produced at warm non-boiling temperatures, so you don’t want to leave your wort in that temperature-range long.As always, practice good sanitation.Commercial ExampleRolling Rock is a commercial beer that has DMS as part of its flavor profile.

Sample #5 What is wrong with this beer?

Ethyl Fenchol (Earthy)Perceived AsEarthy, soil-like, Geosmin – the compound which gives earthy flavour to beetrootFlavour Threshold – 5 μg/lSample - 15 μg/lImportanceEthyl fenchol is a taint in beer. It is associated with a moderate degree of consumer rejection. Earthy taints from ethyl fenchol are sometimes described by consumers as ‘dirty’ or ‘contaminated’.Effect of AgingLikely will increase with age.Caused ByEarthy taints from ethyl fenchol are imparted through use of contaminated brewing water, sparge water or dilution water. The flavour arises from growth of microorganisms in the water supply.

Ethyl Fenchol (Earthy)How To Avoid/ControlFilter your brewing water if using tank water.As always, practice good sanitation.

Sample #6 What is wrong with this beer?

Ethyl AcetatePerceived AsEstery, Fruity, pear like at low quantities - Solvent/nail polish remover, perfume at high quantities.Flavour Threshold – 20-40 mg/lSample - 60 mg/lImportanceEthyl acetate is present in all beers, and is the ester found in greatest amounts in beer. Its high flavour threshold means that it makes a bigger contribution to the flavour of ales - and especially strong ales - than it does to lagers. It is produced by both ale and lager yeasts and is desirable in small quantities in certain styles of beer.Effect of AgingWill not decrease with age.Caused ByParticular yeast strains. High fermentation temperatures. Poor yeast health/inadequate pitch. Lack of oxygen in wort at start of fermentation. High gravity worts.Ethyl acetate can be produced in offensive levels by Brettanomyces when exposed to oxygen. Acetic acid is the precursor to ethyl acetate. Ethyl acetate is a metabolic dead-end, meaning that there is not a known pathway for breaking down ethyl acetate.

Ethyl AcetateHow To Avoid/ControlUse a different yeast strainCreate yeast starterControl and maintain fermentation temp• Lower fermentation temp for certain strainsLower starting gravityAs always, practice good sanitation

Sample #7 What is wrong with this beer?

Ethyl HexanoatePerceived AsEstery, Fruity, Red Apple, Aniseed, FennelFlavour Threshold – 0.2 mg/lSample – 0.6 mg/lImportanceEthyl hexanoate is an ester which is present in all beers. Concentrations of ethyl hexanoate vary from beer to beer. Ethyl hexanoate is a key flavour impact character in some lagers and ales.Effect of AgingWill not decrease with age.Caused ByParticular yeast strains. High fermentation temperatures. Poor yeast health/inadequate pitch. Lack of oxygen in wort at start of fermentation. High gravity worts.

Ethyl HexanoateHow To Avoid/ControlUse a different yeast strainCreate yeast starterControl and maintain fermentation temp• Lower fermentation temp for certain strainsLower starting gravityAs always, practice good sanitation

Sample #8 What is wrong with this beer?

GERANIOLPerceived AsFloral, Geranium Flowers, CitrusFlavour Threshold – 100-200 μg/lSample – 450 μg/lImportanceGeraniol is a positive flavour character of hoppy beers. When oxidized, geraniol becomes geranial or citral. Interestingly, people have differing abilities to perceive geraniol; this difference is thought to be genetically based. One-third of the population has a perception threshold of about 18 μg/l, whereas the remainder of the population has a threshold of around 350 μg/l.Effect of AgingWill decrease with age.Caused ByGeraniol is contributed to beer via hops added in the kettle, during fermentation, or after fermentation. Concentrations of geraniol in beer depend on the hop variety, hopping regimen and process conditions. It is found in Cascade, Citra, Centennial, Chinook, Pacific Hallertau, Southern Cross, Motueka, Aurora, and Styrian Golding hops.

GERANIOLHow To Avoid/ControlUse less/more hopsUse different hop varieties

Sample #9 What is wrong with this beer?

IndolePerceived AsFarmyard, Musty, Faecal, can be Jasmine like in smaller amounts. (*not to be confused with farmyard/horsey aroma produced by Brettanomyces yeast. ) Apparently only 50% of population detect as Faecal.Flavour Threshold – 10-20 μg/lSample – 0.55 mg/lImportanceIndole is an off-flavour in lagers, ales and stouts. It is regarded by some as ‘artisanal’ character (‘jasmine / floral’) and by others as a serious off-note (‘faecal / dirty’).Effect of AgingWill decrease with age.Caused ByIndole is formed by contaminant bacteria during fermentation. It is often associated with simultaneous production of dimethyl sulphide.

IndoleHow To Avoid/ControlAs always, practice good sanitation – equipment, water, EVERYTHING.Use healthy yeast

Sample #10 What is wrong with this beer?

Isovaleric AcidPerceived AsOld cheese, rancidity, old hops, goaty, dirty socks, sweatyFlavour Threshold – 1.0 mg/lSample – 3.0 mg/lImportanceA “sometimes” component of some highly hopped beer styles, but in general is considered an off flavor.Effect of AgingWill mellow with age.Caused ByA result of oxidation of the alpha acids in hops. If associated with alpha acids, it is often accompanied by grassy notes, but it can also be caused by bacterial infection.

Isovaleric AcidHow To Avoid/ControlUse fresh hops; ensure you buy fresh hops that have been stored correctly.Store hops in a freezer in a oxygen free, vacuum sealed container.Age beer that has cheesy notes to help mellow those flavours.Use good sanitation practices.

Sample #11 What is wrong with this beer?

Oxidation - Trans-2-nonenalPerceived AsSherry-like, Papery, like cardboard, stale, oxidized, “old book”. At low levels can have a inky, musty quality.Flavour Threshold – 0.5 μg/lSample – 2.0 μg/lImportanceThis is a flavour associated with the aging process of beer. What qualities it takes on depends on the style of beer and what temperature the beer is stored at. Some flavours associated with oxidation are important components of an aged beer’s profile, others, are always considered off flavours.Effect of AgingOxidation characteristics are very fluid. Some flavours will increase; some will increase then decrease or level off.Caused ByOxidation is directly caused by aging. How fast and to what extent this process occurs is a result of oxygen conditions, storage temperatures, and a beer’s ingredients. The more oxygen a beer is in contact with the faster and more severe the oxidation. Cooler storage temperatures slow the process. There is a marked increase in oxidation as storage temperature increases. Ingredients used in the beer can both inhibit or aid oxidation. Packaging issues.

Oxidation - Trans-2-nonenalHow To Avoid/ControlMinimize aeration of hot wort by avoiding splashing, spraying, or vigorously stirring. (DEBATE)Do not aerate beer after fermentation starts.Work to get good hot and cold break separation.Don’t leave more than 1 to 2 inches of head space when bottling.Use ant-oxidant bottle caps and cap on foam if possible.When possible, purge kegging equipment with CO2 before using.Keep beer below 10°C if cellaring.Don’t age beer unless it’s meant to be aged.

Sample #12 What is wrong with this beer?

Spicy - EugenolPerceived AsBitter, spicy, herbal, drying, tea-like, clove-like.Flavour Threshold – 40 μg/lSample – 120 μg/lImportanceThis is usually considered an off-flavour, but can make up a small element of the character in stouts and other ales, and is also a major contributor in German wheat beers.Effect of AgingWon’t really increase or decrease, if it’s in the beer it’s generally there, at that level, for good.Caused ByCan be caused by wild or specialty yeasts, contaminations, Chlorophenol presence in tap water, chlorine sanitizers, and improper sparging technique.

Spicy - EugenolHow To Avoid/ControlUse yeasts that will produce fewer phenols.If brewing with tap water, be sure to filter it first.Either rinse well after using chlorine sanitizers or use non-chlorine sanitizers, such as Star San.Use pure yeast strains and take proper precautions to avoid wild yeast contamination during fermentation.Don’t over-crush your grain.Don’t collect wort below 1.008 SG.Keep sparge above 6.0pH and temperature below 76°C.