FLAVOR NOTE
TYPICAL DESCRIPTORS
Eugenol
Spicy-clove, allspice, 4-(H2C=CHCH2)C6H3-2- cinnamon, ginger, aromatic and nutmeg (not to be confused (OCH3)OH with similar notes from [C10H12O2] guaiacols which are in fact more smoky spicy-like). [4-allyl-2-methoxyphenol]
FLAVOR THRESHOLDS* COMMENTS AND NOTES Taste threshold 50 ppb in 20% ethanol and a recognition threshold of 4.9 ppm in 23% grain spirit. Notable in Bourbon and Canadian whiskey with low ppb recognition. Grain whisky at odor threshold at four years.
Major volatile phenol derived from oak. Like most phenolics extracted from wood, arises by alcoholysis of lignin (“splitting of lignin by alcohol”). Increased by thermal degradation of oak. Arises from new staves after charring and ethanolic extraction or from cereal cell walls. Eugenol or clove buds easy to obtain and use as training guides to illustrate the aromatics of a general class of phenolic flavor compounds.
Furfural
(2-Furaldehyde – C5H4O2) and 5-hydroxymethyl furfural (HMF, 5-hydroxymethyl-2furaldehyde – C6H6O3)
Fusel oils
FUSEL OILS (ALCOHOLS)
(several compounds – Main players): 2-Methyl-1-Butanol (Active amyl alcohol) CH3CH2C(CH3)2OH 3-Methyl-1-Butanol (Isoamyl alcohol) (CH3)2CHCH2CH2OH
Sweet, butterscotch, caramel, smoky, almond nuances.
Alcoholic, spicy, vinous, pungent and warming. Poorly rectified spirit aroma with the rubbing alcohol-like solventy notes. Several alcohols are involved and these being higher boiling point volatiles than ethanol are considered “tails” compounds.
C6H5CH2CH2OH
The main fusels – active and Isoamyl present at 410-475 ppm in Scotch, 150-230 in Canadian, 1685 in Bourbon and 422-990 ppm in French Brandy.
Rose-honey-like, floral, sweet
Typical values given as 5-32 ppm in whiskeys and 130 ppm in straight Bourbon.
[C8H10O]
Guaiacol
[2-methoxyphenol] (CH3O)C6H4OH C 7H 8O 2
Hydrogen sulfide H2S [Sulfidic]
Cis and trans isomers β-methyl-γ-octalactone C9H11O2
Formed in fermentation in metabolic reactions involving amino acids. The amino acid leucine leads to isoamyl alcohol and iso-leucine leads to active amyl alcohol. Any condition that stimulates yeast growth will stimulate fusel oil production.
While this is a so-called mixed aliphatic (long chain)/aromatic (contains a ring structure) alcohol with different properties to those fusel oil components listed above, it is actually a fusel alcohol. Derived from the amino acid phenylalanine it is produced during fermentation – so its formation is yeast and fermentation condition dependent. It adds a positive note to spirit flavor/aroma.
Threshold in water 5 ppb!
Rotten egg, hard-boiled eggs, hair permanent solution.
0.005 ppm (0.5 ppb – parts per billion!]
Produced by yeast during fermentation – so yeast strain dependent production. Can also be produced by contaminating bacteria.
Vanilla, ice-cream, vanilla bean.
Threshold 0.1 ppm in water. Notable as a key component in Bourbon and perhaps a big part of the “Angels share” aromatics in the Bourbon warehouse?
Vanillin is the main aroma component of natural vanilla. Significant amounts in oak wood. Increased up to a point by toasting – decreased at high toast level. See Figure 2.
Recognition threshold at 1 ppm in 23% grain spirit whisky. Lactones are important aroma compounds and present in notable amount in Jamaican Rum.
Important oak derived flavors – from oak lipid oxidation. Seasoning barrels affects the ratio of the cis and trans isomers. Toasting may reduce overall levels. American oak shows higher lactone amounts than for other (French) oak species. Notable in matured spirits in new charred casks and at higher concentrations in higher alcohol strength spirit maturations.
4-(HO)C6H3-3-(OCH3) CHO
Whisky (or Oak) Lactone
The fusel oils are a complex mixture (maybe 40-50 distinct components) of aliphatic alcohols – longer chain alcohols than ethanol with correspondingly higher boiling points as length increases. Includes: 1-propanol, 2-methyl propanol (75 ppm threshold) including the major components 2-methyl butanol and 3-methyl butanol – the amyl alcohols. A typical fusel oil contains 60-70% of the amyl alcohols.
Guaiacol and related compounds in general contribute char-like, smoky and spicy aromas
Vanillin
[4-hydroxy-3methoxybenzaldehyde, vanillic aldehyde]
Produced by heat-induced degradation of sugars and carbohydrates – caramelization reactions. Generated during toasting. See Figure 2.
Have arguably been associated with hangovers. Unpleasant in most situations at very high concentration.
Phenethyl alcohol [2-phenylethanol]
Furfural – threshold in water 8 ppm.
Coconut. cis – also with earthy herbaceous notes. trans – coconut and spice character. [“Oaky – oakwood aroma”)
Formed by degradation of the lignin component of wood during toasting and charring (pyrolysis reactions). Higher toast levels = more guaiacols. [See also Eugenol and Figure 2]
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