Fifteen Years Is A Long TIme in Beer

In the late nineties an old chum of mine was a brewer at Youngs (then still very much in Wandsworth). At the time we we're hanging out, drinking beer, as you do. I was also drinking second-hand brewing knowledge from my Heriot-Watt-educated pal. My old chum gave a Word document of off flavours and aromas from Youngs. 

The document has hung around on my various computers ever since. I was reading it again recently when number 13 shouted at me from the screen. Hop aroma is an off aroma! How times have changed.

(yes, I know it says "this is desirable...." but this is a document about off-flavours and aromas)

Flavour	Associated terms	Description	Common Causes
1. Sour	Acidic, Sharp, Lemon, Sour Milk, Vinegar	Beers are naturally acidic however, an excess of acid can lead to an undesirable flavour and mouthfeel. NB. Beer may still be bright.	Mostly a problem on cask beers.  From raw materials, fermentation and bacterial infection in the presence of air.  The latter may be caused by: 1. Beer on dispense too long 2. Poor hygiene, dirty equipment 3. Beer sat in buckets being returned to casks.
2. Phenolic	Diacetyl, Cloves, Lactic, Wild Yeast	A variety of off-flavours may accompany this, but diacetyl is usually the most prominent. Phenolics are a necessary flavour characteristic of some beers e.g. Wheat beers.	1. Produced by speciality yeasts used in wheat beers. 2. Produced as an off-flavour by wild yeast/bacterial infection in presence or absence of air.  Often accompanied by haze formation and can affect cask or keg beers.  The cause is usually poor cellarmanship.
3. Aldehyde	Apple, Grassy	High concentrations lead to off-flavours.	Bacterial infection (acetic bacteria) produces acetaldehyde as a by-product of metabolism of alcohol to vinegar (acetic acid).
4. Diacetyl	Buttery, Butterscotch, Modern Margarine, Milky, Vanilla	Off-flavour in Lagers, which are particularly susceptible, normally removed during maturation period.  ‘Cheap’ continental lagers may have high levels due to rapid processing in the brewery.  Higher levels are desirable in ales were diacetyl makes a positive contribution to flavour. 1 in 3 people tend to be sensitive to low levels of diacetyl.  Some may find it pleasant at relatively high levels.	1. Inadequate removal of diacetyl during maturation, however this will be detected at the brewery. 2. Formed by contaminant bacteria when hygiene standards are poor.  This is the most common cause and can usually be related to poor line cleaning, or not pulling beer through.  The first beer pulled through after standing overnight usually has a high level, where beer is in contact with air in the uncooled part of the system.  This is exacerbated by illuminated T-bars, as the beer is heated.

5. DMS (Dimethylsulphide)	Cabbage, Cooked Veg., Sweetcorn, Seaweed, Tomato Sauce, Oniony, Strawberry Jam.	Desirable characteristic of most lagers, but an off-flavour in some beers. e.g. high levels are found deliberately in Stella Artois and Lowenbrau, but very low levels are found in Budweiser.	Formed from a malt derived precursor during beer production.  May also be produced by contaminant bacteria during fermentation.
6. Estery	Fruity, Banana, Peardrop (iso-amylacetate)	Beer is a delicate balance of esters.  The flavour depends on which esters are predominant, each contributing its own characteristics.	Many factors in brewing affect ester formation, especially yeast strain and type of fermentation vessel.  Handling in the pub is unlikely to affect the balance of esters.
7. Chlorophenolic	TCP	TCP, mouthwash type taste.  Often has a harsh after-bitterness.  Individual susceptibility to this flavour is highly variable.  Some may find it objectionable at even very low concentrations.	Taint from hypochlorite in cleaning fluid, especially if used too hot or left in the lines for long periods.  The fault could originate in the brewery but is normally associated with dispense.
8. Caustic	Biscuity, Detergent	May leave a burning sensation on the tongue.	Again, contamination by cleaning fluid if line cleaner is not rinsed sufficiently .  Lines should be checked for soapiness by rubbing the rinse water with the fingers, and the final flushing water smelled and tasted before beer is pulled through.
9. Oxidised	Cardboard, Stale, Bready, Biscuity	Mainly affects canned/bottled products and old kegged beers	Air/oxygen in package, coupled with high pasteurisation temperatures.  These stale flavours develop faster with high temperatures and with age, hence the importance of temperature controlled storage and stock rotation.

10. Sulphury (H2S)	Rotten Eggs, Sulphur	Imparts a desirable flavour at low concentrations and an off-flavour at high concentrations.	1.Brewing product.  Produced by yeast during fermentation and occasionally during maturation. 2. May be a product of bacterial infection due to poor hygiene standards.
11. Mercaptan	Oniony, Drains, Rotten Vegetables,	Natural part of a beers character which becomes an off-flavour when present in excessive quantities.	Formed by yeast during fermentation and also by yeast autolysis during maturation.
12. Lightstruck	Skunky, Sunstruck	Mercaptan has a very low flavour threshold, therefore, only very small amounts need be present in the beer to make it unpleasant.	Formed when beer is exposed to daylight or artificial light.  Therefore mainly a problem in beers packed in clear glass bottles, or pints of beer drunk in beer gardens during summer.  An exposure time of ten minutes on a sunny day can be enough to have a serious effect on beer flavour. The flavour comes from modification of the hop compounds in the beer, therefore beers produced with specially modified hop products will not develop this flavour.
13. Hop Aroma	Hoppy	Hop aroma is not the same as Bitterness.  It does not impart any more bitterness to the beer, but gives a pleasant hoppy smell and taste.	Produced by addition of hops late during copper boil or by dry-hopping (addition of a hop pellet to cask).  This is desirable and forms a significant part of the beer character