Wine · Terminology

Fortification

Adding grape spirit to wine — raising the alcohol and, if done mid-ferment, leaving it sweet.

Fortification is the addition of a neutral grape spirit — usually around 77% abv — to wine, taking it to roughly 15–22% alcohol. It began as a preservation technique for wines shipped long distances, and became the foundation of some of the world's greatest styles.

The crucial variable is when the spirit goes in. Yeast cannot survive much above 15% alcohol, so fortifying during fermentation kills it and leaves the remaining sugar in the wine; fortifying after fermentation has finished gives a dry fortified wine.

In practice

  • Mid-fermentation fortification (mutage): sweet. Port, Vins Doux Naturels such as Muscat de Beaumes-de-Venise.
  • Post-fermentation fortification: dry. Sherry — Fino, Manzanilla, Oloroso.
  • Fortification level also decides the ageing path for Sherry: ~15% permits the flor veil to grow; ~17% kills it and forces oxidative maturation.
  • Madeira adds heat — estufagem — on top of fortification.

Where you'll meet it

  • The fortified wine guide.
  • Portugal: Port and Madeira.
  • Spain: Sherry from Jerez, and Málaga; France: the Vins Doux Naturels of Roussillon.

The classic styles

Style Fortified Sweetness Ageing
Port (Ruby, LBV, Vintage) Mid-ferment Sweet Reductive, in bottle for Vintage
Tawny Port Mid-ferment Sweet Oxidative, in cask — 10/20/30/40 years
Fino / Manzanilla Sherry After ferment, to ~15% Dry Biological, under flor
Oloroso Sherry After ferment, to ~17% Dry Oxidative
Amontillado After ferment, then re-fortified Dry Flor first, then oxidative
Pedro Ximénez Mid-ferment, sun-dried grapes Intensely sweet Oxidative
Madeira Varies by style Dry to sweet Heated (estufagem), then long cask ageing
Vin Doux Naturel Mid-ferment Sweet Both, depending on style

Why the timing works

Fermentation stops when the yeast dies. Adding spirit to a must that still holds, say, 100 g/L of unfermented sugar arrests it instantly and locks that sweetness in — the same outcome as chilling or filtering, but permanent and stable. This is one of the clearest illustrations of how residual sugar actually arises.

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