The importance and origins of each flavour are:

Flavour: GRAPE-LIKE    Chemical name: 2-AMINOACETOPHENONE

“Grape, like acacia flowers, tortillas or grape juice”

IMPORTANCE: Imparts a fruity, grape-like odour to wine, reminiscent of lime blossom, putty and taco shells depending on the concentration. Associated with the atypical (premature) ageing of white wine when it is often found together with sotolon. The key drivers of this fault are not fully understood though vine stress during drought conditions is known to be involved.

ORIGINS: Varietal character contributed through use of certain grape varieties (eg Vitis labsrusca). Also formed from tryptophan present in wine. Associated with ageing in the absence of lees and use of new barrels.

Flavour: ROTTEN VEGETABLE    Chemical name: DIMETHYL DISULPHIDE

“Rotten vegetable, like pickled vegetables or a sewage treatment plant”

IMPORTANCE: Dimethyl disulphide imparts a sulphury off-flavour to wine, reminiscent of rotten vegetables and asparagus. The compound can also arise during wine making via methanethiol from degradation of sulphur-containing fungicides applied to grapes.

ORIGINS: Produced in wine through oxidation of methanethiol. Its presence is indicative of wine oxidation or ‘stressed’ fermentations. Exposure of wine to light can also lead to formation of dimethyl disulphide and other sulphur compounds.

Flavour: HONEY    Chemical name: ETHYL PHENYLACETATE

“Honey, like sweet mead or sherry”

IMPORTANCE: At low concentrations ethyl phenylacetate imparts a pleasant sweet, ‘honey-like’ note to wine. The presence of this note is associated with high quality white wines, such as Sauternes and Tokaji in vintage years. The compound has been confirmed as a cause of a sweet flavour detect in Italian Aglianico del Vulture reds.

ORIGINS: Produced by yeast during maturation of cider from phenolic precursors. Concentrations may increase after packaging as a result of non-enzymic reactions.

Flavour: EARTHY-GREEN PEPPER    Chemical name: 2-ISOBUTYL-3-METHOXYPYRAZINE

“Earthy, like green pepper”

IMPORTANCE: At low levels imparts a desirable herbaceous, bell pepper, varietal character. Too much suggests insufficient maturity of the grapes. It is regarded as an off-flavour at higher concentrations or in some wine styles. Isobutyl methoxypyrazine is one of several methoxypyrazines found in grapes and wine.

ORIGINS: Contributed by certain grapes as a varietal character. Higher levels of methoxypyrazines are associated with under-ripe grapes and the presence of vine stem material during extraction of juice.

Flavour: ISOVALERIC    Chemical name: ISOVALERIC ACID

“Isovaleric, like stale cheese or sweaty socks”

IMPORTANCE: Imparts an odour of stale cheese or sweaty socks. Growth of Brettanomyces can add complexity to the product. Excessive growth leads to spoilage, imparting a distinctive and undesirable ‘Brett’ character.

ORIGINS: Formed by contaminant Brettanomyces during maturation of wine or as a result of spoilage in bottle.

Flavour: MERCAPTAN    Chemical name: METHANETHIOL

“Mercaptan, like drains or rotting garbage”

IMPORTANCE: Component of the sulphury flavour character of wine. Found in all wines to a degree. Off-flavour when present in excess. Supplementation of must with ammonium salts prior to fermentation can help control formation of mercaptans.

ORIGINS: Arises through yeast autolysis at the end of fermentation or during maturation. Formation of high levels by yeast can be indicative of a deficiency of amino acids in the must and ‘stressed’ fermentations.