Fortified wine is made by ‘fortifying’ a table wine by adding a strong spirit, usually grape spirit (like brandy). The increased alcohol content prevents most bacteria and yeast from working, stops fermentation and stabilises and preserves the wine. When exactly you add the spirit is what decides the style, as in the difference between the two most famous fortified wines - Port and Sherry. With Port, the spirit is added before fermentation is finished, leaving some sugar unfermented and producing a sweet drink. With Sherry, it is added later, and so in its natural state Sherry is dry. Resolutely undervalued, the best fortified wines currently represent astonishing value.

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