Fortification

What it is

Fortification is the addition of wine-derived spirit (concentrated grape alcohol, usually 60-95% ethanol) to a wine to raise the final alcohol level. In Andalusia aguardiente or destilado de vino is used. For sherry it is a mandatory step that also defines the style direction.

The timing of fortification makes the difference:

• Before fermentation completes: spirit halts fermentation, residual sugar stays high. Result: sweet wine (port style, some Moscatel styles).
• After fermentation completes: all sugar has converted, spirit just raises alcohol. Result: dry wine (sherry Palomino style).

For sherry it’s almost always the second: ferment to dry (~11% alcohol), then fortify to 15-22%.

The flor threshold

The critical value in sherry is 15.5% alcohol. Below that threshold flor yeast grows on the liquid surface; above it the yeast dies. Cellar masters use this threshold deliberately:

• Fino/Manzanilla: fortified to 15-15.5%. Flor lives, wine ages biologically under the yeast veil.
• Amontillado: starts under 15.5% (as fino), later fortified to 17-18% to kill flor before the oxidative phase.
• Oloroso: fortified to 17-18% directly, no flor. Fully oxidative ageing.
• Palo Cortado: similar to oloroso, but started as fino with natural flor death.

A difference of two or three alcohol percent decides the whole flavour route. No other aspect of sherry production carries such a strict binary.

In other wines

Fortification is not a sherry invention. Major other applications:

| Wine | Timing | Final alcohol | Result | |---|---|---|---| | Port | During fermentation (~7%) | 19-22% | Sweet, residual sugar preserved | | Madeira | During fermentation | 17-22% | Sweet or dry, heat-aged | | Marsala | After fermentation | 17-20% | Variable, dry to sweet | | Banyuls | During fermentation | 16-22% | Sweet, Grenache-based | | VDN (France) | During fermentation | 15-22% | Various styles |

For port and VDN, fortification is a sweetness-preservation tool. For sherry it is primarily a style-defining tool through the flor threshold.

What fortification is not

The common explanation sometimes presents fortification as “adding alcohol to make it last longer”. Half-true: higher alcohol slows spoilage, but that’s not the main goal. For sherry, fortification is mainly a style-steering tool. For port it’s a sugar-preservation tool.

A second misconception: fortification would make the wine “less natural”. The spirit comes from the same grape as the base wine. The difference is concentration, not origin. Spirit is wine that has been heated to vapour and condensed back to liquid.

Frequently asked questions

What kind of alcohol is used for fortification?

Wine spirit (aguardiente in Spain). Not industrial alcohol, not grain alcohol, not other spirits from outside the wine world. Per-DO rules require spirit from the same country or even the same region. For sherry: spirit from Spain, almost always from Andalusia.

Can the spirit come from a different grape than the base wine?

Generally yes, provided the spirit grape is approved for the DO. Many sherry bodegas use spirit from Airen or Palomino. For port the spirit source can be broader, as long as it comes from approved Portuguese grapes.

Is there such a thing as unfortified sherry?

Since 2021 yes: Vino de Pasto and Vino de Jerez sin fortificar. Still white wine from Palomino without spirit addition. A separate DO category, with a handful of producers. Not the same as classical sherry, more a related still white style on the same soil.