1. Beer Flavours
Since I have had a crack at judging it occurred to me that some research into the various components such as "esters" and "phenolics" that judges talk about wouldn't go astray.
Contents
2. The Beer Flavour Wheel
3. References
- aaba domain defunct
Use Your Common Senses A short but informative article on evaluating beer.
Factors affecting the formation of fusel alcohols during fermentation
SYNTHESIS AND PURIFICATION OF 36 AROMATIC CHOLINE ESTERS AS STANDARDS
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4. Diacetyl
Diacetyl is commonly described as buttery or butterscotch. It can also be produced by bacteria such as Pediococcus sp.
Generally removed by diacetyl rest after fermentation which is a period of say 48 hours at 16°C.
5. Acetaldehyde
Fresh cut green apple flavours.
6. Phenolics
They are considered as a signature in certain styles such as wheat beers "underlying spicy clove-like phenols and fruity (banana) esters complementing." and low levels are acceptable in Australian Bitters. They are also "part of the style" for most belgian beers.
Phenols can also react with chlorine to form chlorophenols. Some of these have very low taste thresholds. Chlorophenols smell like band-aids or nappies (unused ones), or a distinctive plasticy/medicinal aroma. (note: If your beer smells like a used nappy then you have other problems).
From 2:
When many of the more pungent compounds were added to samples of normal beer, our taste panel had no difficulty in noting the phenolic or medicinal character which they imparted. The detectable levels in beer are somewhat higher, in most instances, than those in water. For example, 30 ppm. phenol, 20 ppb. o-cresol, and 15 ppb. 4-chloro-2-methyl phenol (chlorocresol) were needed for detection. However, only !2 or 3 ppb. of o-chlorophenol gave a distinct off-character to beer. When the taste panel was asked to indicate which phenolic compounds, when added to beer, most closely matched the offcharacter of a brewery beer, it chose ochlorophenol and 4-chloro-2-methyl phenol as being close duplicates, with o-cresol and chlorohydroquinone also being quite similar. It is quite possible that other phenols and chlorophenols that we have not checked will also produce similar flavors. The majority of the simpler phenols reported to he present in beer are rather difficult to obtain, particularly in their chlorinated forms.
From 4:
However, the most common source of phenolic flavors in beer comes from yeast. Some yeast strains produce phenolic flavors as a normal part of their metabolism. These strains have enzymes that other brewing yeast lack. The phenolic flavors originate from phenolic acids naturally found in malt, especially ferrulic acid. Strains of yeast with the right enzymes transform these phenolic acids through a decarboxylation reaction into aromatic phenols, such as 4-vinyl guaiacol. These compounds are often described as possessing clove-like and vanilla aromas.
7. Esters
These are formed by the reaction of an alcohol and a fatty acid. Because fusel alchol production is increased with increasing fermentation temperatures, the complexity of the ester profile is also increased.
Ester |
Characteristic Aroma |
Notes |
Isoamyl acetate |
Banana |
German wheat beer yeasts and higher fermentation temperatures. Higher pitching rates contribute more. |
Isoamyl butyrate |
Pear |
. |
Ethyl acetate |
juicy fruit |
. |
From Dr Cone on HBD:
Ester and other flavor component production or synthesis is a complex subject because there are so many variables taking place at the same time. You are right, ester production is related to yeast growth but not in the way you might think. The key element to yeast growth and ester production is acyl Co-A. It is necessary for both yeast growth and ester production. When it is busy with yeast growth, during the early part of the fermentation, it is not available for ester production. Ester production is directly related to biomass production. Everything that increases biomass production (intensive aeration, sufficient amount of unsaturated fatty acids, stirring) decreases ester production. The more biomass that is produced the more Co-enzyme A is used and therefore not available for ester production. Anything that inhibits or slows down yeast growth usually causes an increase in ester production: low nutrient, low O2. It has been noted that a drop in available O2 from 8 ppm down to 3 ppm can cause a four fold increase in esters. Stirring in normal gravity decreases ester production. Stirring in high gravity increases ester production. CO2 pressure in early fermentation decreases ester production. Taller fermenters produce less esters than short fermenters. High temperature early in fermentation decreases ester production. High temperature later in fermentation increases ester production. Low pitching rate can result in less esters. There are other flavor components such as higher alcohol that have there own set of variables. Stirring increases production of higher alcohols. CO2 pressure does not effect the production of alcohol. Amino acid levels in the wort effect the production of higher alcohols. Most of the higher alcohol is produced during the growth phase (exponential phase) of the yeast. I am sure that there are many other variables. I am also sure that there are beer makers that have experienced the very opposite with each of the variables.
8. Oxidation
Oxidation is normally associated with a cardboard aroma but it can also be described as mautre pineapple, and in later stages winey or madiera-like.
9. Lactic Acid
Lactic acid gives beer a sour (as in sour milk, not vinegar) taste. From 6:
The result of lactic acid, which is produced by lactic acid bacteria; detected as a sour sensation on the sides of the tongue; acceptable in some styles, but generally indicates a sanitization problem; the growth of lactic acid bacteria is inhibited by high hopping rates.
10. DMS
from 10:
Dimethyl Sulfides (DMS)/ Cooked Vegetable Flavors
Like diacetyl in ales, DMS is common in many light lagers and is considered to be part of the character. DMS is produced in the wort during the boil by the reduction of another compound, S-methyl-methionine (SMM), which is itself produced during malting. When a malt is roasted or toasted, the SMM is reduced beforehand and does not manifest as DMS in the wort, which explains why it is more prevalent in pale lagers. In other styles, DMS is a common off-flavor, and can be caused by poor brewing practices or bacterial infections.