Wine is no more than the fermented juice of grapes. Yeast, either naturally occurring or cultivated and added to the must (grape juice) acts on the sugar to form alcohol and carbon dioxide. Innumerable other reactions happen at the same time, turning the flavour components in the grapes into the flavours we expect in wine. For Port there is one other vital ingredient, high-strength, relatively neutral grape spirit, added to kill the yeast half way though the fermentation to preserve a high degree of natural sugar.
Nearly all grapes have green pulp, so for red wine the skins have to be included in the fermentation vat to extract colour, and tannin. For light wine, ordinary red wine, the skins are kept in contact with the fermenting must right through the fermentation, and often even longer to ensure sufficient colour and tannin are extracted, anything for a week for lighter styles up to a month for the richest and fullest wines destined for long cellarage. For Port, having the fermentation is arrested part way through, fermentation lasts a mere day and half, two days at most, so the top priority for the Port winemaker is rapid, but appropriate extraction.
Colour fades in time, and tannin acts as a preservative, but since the wines that are going to age for decades, thorough extraction is particularly important for. Bear in mind also that the spirit used for fortification makes up roughly one fifth of the total volume. It is water-white and will therefore dilute the colour.
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Traditionally the best Ports have always been made by treading the grapes, the action of dozens of human feet squeezing the skins against the stone floor of the lagar, the granite fermentation vat, still considered the best means of rapid extraction.
For more details on treading, see the features section on robots making Port.
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Each vat consists of two vessels, one main tank with an open trough above, connected by one open pipe that extends down below the surface of the wine, and drain contraption that looks like an overgrown test-tube. In addition there is a simple water valve that regulated the pressure in the main tank. Grapes are crushed and loaded into the main tank. As fermentation progresses the carbon dioxide pressure forces must from the bottom of the tank into the open trough at the top. When a certain volume of must has been moved, the water valve releases the pressure and gravity draws the wine down the central plumbing and it sprays down over the cap.
The advantages are easy to see. Low labour costs and almost no requirement for external power, but extraction relies on the speed of fermentation. In cold years they do no get going very easily, and in warm years they operate too quickly. Furthermore there is no prefermentation extraction, in direct contrast to the other methods employed.
Early autovinifiers were made of concrete, which led to difficulties with temperature control, and need careful lining with wine-resistant epoxy paint. Modifications to the basic design have included water pipes running through the pipe-work to aid temperature control, and even little propellers connected to the pipes so break up any skins that passed them, this latter modification being generally considered unsuccessful. The latest versions, as epitomised by those at Symington's Quinta do Sol, are made of stainless steel and incorporate both autovinification technology and modern pumps to pump the must over the cap before fermentation starts.
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Latest developments, paradoxically, go back to basics and attempt to mimic the action of feet in the lagares. Initially normal tall cylindrical, closed-topped, stainless steel vats were fitting with paddles to punch down the cap, but the latest versions have gone back to the wide, shallow, open vats.
Irrespective of the fermentation vessel used, the second key task of the Port wine maker is fortification. Timing is all-important because the shipper's house style is, largely, dependent on the sweetness of the finished wine. In any normal winery the vats are left alone overnight. Temperature control is less of an issue at night, especially with modern automatic cooling systems, and if a wine reached the end of it fermentation at four o'clock in the morning it will not come to any harm if left until after breakfast. Port, however, has to be managed. If a particular vat reaches the required sugar level at an unsociable hour, it has to be fortified then. With fermentations carrying on apace, a delay of even a couple of hours will result on the wrong style of wine. The winemaker has to be on-call overnight here.
One key advantage of the latest fermenters is the speed of emptying. Fortification happens when the fermentation is at its most rapid, the sugar level is dropping at its fastest rate, so the time taken to empty the vat can result in a significant drop in sugar levels in the finished wine. Emptying a lagar is a slow and labour-intensive process, modern punching-down vats and, in particular, the latest robotic lagars are designed to reduce the time taking in this final stage.
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Sugar levels are measured here in Beaumé (Bé), each degree of Beaumé being approximately equal to 17 grammes per litre of sugar, or one percent potential alcohol. Grapes for the best wines will come in at about 14 Bé, with fortification happening, therefore fermentation halted, when the must reaches about 8 Bé. The exact level will vary from one producer to another because the level of sweetness in the final wine is a significant part of the house style. The spirit does not come from the region, rather it is sourced from anywhere within the European Union, typically it is the distillate of the French or Italian wine lake. Keep an eye on the Features Section for a forthcoming article on Spirit.
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However the wine has been made, it is its subsequent maturation that gives us the different styles. All red Port is essentially made in the same way, whatever the winery equipment looks like. Of course there are vineyards that will only even made the inexpensive Ruby and Tawny styles, and these grapes might be given less attention when it comes to extraction, whereas the best grapes, from prestige vineyards, will be those most likely to go into the lagar, or the robot. The aim, at whatever level though, is to get the extraction.
Traditionally the young Port was mostly shipped down the river Douro to Vila Nova de Gaia, the south side of the river at Oporto, where the climate is cooler and the wines mature more evenly.
Once finished, the winemakers will assess the wines and their future will be decided. This typically starts in the spring after the vintage. Winemakers are looking initially to separate the basic qualities that will not age, from those with the intensity and structure to age for the decades we ask of the finest Ports. Even the basic wines have to reach a certain standard; Ruby Port has to have a certain finesse and fruitiness to be attractive.
See Port Styles for more details on the resulting varieties of Port on offer.
The style of any given Port relies more of its selection, blending and maturation than on the vineyard site.