Altitude

Altitude has become a marketing term as much as a viticultural one, and the claims made for it outrun what elevation on its own determines.

What matters is the combination of elevation with latitude, aspect, and local air movement — a high vineyard near the equator and a high vineyard in Europe are not comparable.

Air temperature falls with height at a rate of roughly 0.6°C per 100 metres in the free atmosphere, though local conditions modify this considerably.

Diurnal range is generally wider at altitude, because thinner, drier air radiates heat away faster at night. Cool nights slow the respiration that consumes malic acid, which is the mechanism usually cited for altitude and acid retention.

Ultraviolet radiation increases with elevation, and is associated with thicker skins and higher phenolic and anthocyanin concentration — a tannin and colour effect rather than an acid one.

The growing season shortens, because spring warmth arrives later and autumn cold earlier, and frost risk at both ends increases.

Temperature inversions complicate all of it: cold air drains downhill at night and pools in valley bottoms, so a mid-slope site can be warmer overnight than the valley floor below it.

High-altitude sites at low latitude can be extremely hot by day despite a low mean, which is why Mendoza’s Uco Valley and Etna produce quite different wines despite both being described as high altitude.