The Fortification Process


Port is a fortified wine. Fortification involves adding a small amount of grape spirit – a colourless, neutral spirit distilled from wine - at some point in the wine making process. In the case of Port, the fortification process works like this.
When the grapes have been picked, they are carried to the winery where they are crushed to allow the fermentation to start. Fermentation is the process common to all wines whereby the sugar in the grape juice is converted into alcohol by micro-organisms known as yeasts. 
Once fermentation is under way, care is taken to ensure that the grape skins are kept in constant contact with the fermenting juice so that their colour, tannin and flavour are released into the wine.
Traditionally this is achieved by treading the wine by foot in wide granite tanks called ‘lagares’, a process used nowadays only by top Vintage Port producers like Croft. In most wineries, foot treading has now been replaced by mechanical methods.
When about half of the natural sugar in the grape juice has been turned into alcohol, the treading stops and the skins are allowed to float to the surface of the ‘lagar’.
The fermenting wine is then drawn from under the skins into a vat.  As the fermenting wine runs into the vat, the grape spirit is added to it. This raises the strength of the wine and stops the fermentation. As a result much of the natural grape sugar is preserved in the finished Port. 

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