Treading grapes for Port

Many thanks to Cristiano van Zeller who sent me various photos of grape treading in Quinta Vale de Dona Maria. I chose this picture from the 2008 vintage for this entry. In the bottom left hand corner, you can see a lagar filled with grapes and the one on the right is full of people treading grapes. You can see from their legs that the lagar is quite deep, the level of grape and juice is above everybody's knees!

Why tread grapes? Red grapes, like white ones, are normally white fleshed, so the juice is basically colourless. It is only by macerating the skins for some time in the juice that the colour is extracted, which is what happens in the fermentation of normal red wines. But Port is fortified and the fermentation is cut short by the addition of alcohol to preserve the grape sugars in the finished product. The short fermentation and maceration may not be sufficient to extract all the colour and interesting matter from the skins. By having people to tread them, the agitation caused by the treading helps extract the colour etc from the skins. They have only been in the lagar for hours, not days and their thighs are already deep red with the grape juice. There is supposed to be a recommended number of people per tonne (or whatever unit weight) of grapes. I once read that Dirk Niepoort is obsessive enough with extraction to have twice as many people in the lagar. Cristiano van Zeller tells me that this is unlikely to be the case, but like everyone in the Duoro, if you have nothing better to do, you go into the lagar.

What are the alternatives to treading? There are robot treaders, and I think some just pump the juice from the bottom of the tank and release the juices over the pressed grapes. Yet all the best Ports are trodden - just a matter of tradition, or the superiority of the human feet?