Wine Arcana

Concept

Wine aroma

Wine aroma is the smell produced by volatile compounds reaching receptors in the nose. Some arrive when a person smells the glass; others travel from the mouth to the nose during drinking. This second route helps explain why a wine's flavour includes more than the tongue's sensations of sweetness, sourness, and bitterness.

Grapes supply both aromatic molecules and precursors that become aromatic later. Yeast, bacteria, maturation vessels, oxygen exposure, and bottle age add or transform further compounds.

Grapes and precursors

Varieties differ in the compounds they can produce. Monoterpenes help explain the floral expression of Muscat, while methoxypyrazines can contribute green or herbal notes to Cabernet grapes. Their concentrations depend on the vine's genetics and its growing conditions.

Some precursors have little smell until enzymes or fermentation transform them. Consequently, tasting a berry and smelling its finished wine can give quite different impressions. Harvest date and fruit exposure change the available material, while extraction and microorganisms influence what becomes perceptible. Lin and colleagues review these relationships between grape genetics, biosynthetic pathways, and wine aroma.1. Lin, Massonnet & Cantu (2019), review of varietal aroma and its genetic and biochemical origins.

Fermentation and maturation

During alcoholic fermentation, yeast produce esters, higher alcohols, and other volatile compounds. The yeast population, temperature, nutrition, oxygen, and juice composition affect the result. Fruit-like smells can therefore arise through fermentation without the corresponding fruit being an ingredient.

Malolactic fermentation can contribute buttery character through diacetyl, although its perception depends on production and subsequent transformations. Oak maturation supplies another source of aroma and changes oxygen exposure. Barrel toast, size, age, and the duration of contact influence how much wood character enters the wine.

In bottle aging, some compounds decline while others form or become easier to perceive. The familiar terms primary, secondary, and tertiary refer broadly to grape, fermentation, and maturation aromas, although their chemistry overlaps.

Why the same compound can smell different

Concentration matters relative to a compound's detection threshold, but the threshold itself depends on the surrounding mixture and the person smelling it. Compounds can reinforce, mask, or change the interpretation of one another. The smell of the whole wine is therefore not a simple inventory of every molecule detected by an instrument.

Serving temperature, glass handling, and time after opening also change the material reaching the nose. Comparisons become easier when wines are served under similar conditions and revisited as they warm.

Describing an impression

A specific, familiar comparison can communicate an aroma efficiently. One reader may identify a flower or fruit where another notices only a broader floral or fruity impression.

Aroma intensity is also separate from body and texture. An expressive wine can feel light, and a substantial wine can smell restrained. Oxidation, reduction, and Brettanomyces provide further context when a particular smell needs investigation.

Sources