In a nutshell: Deep, sweet, strong wine, mostly very consistently made in several different styles.
Main grapes: Touriga Nacional and myriad others.
Although there are wines made outside Portugal to taste like port (see below), there is nowhere in the wine world at all like the Douro Valley in northern Portugal, the true home of port and any wine like it. The peasant farmers who inhabit this wild, silent valley in which only the vine will grow, rely for their livelihood almost entirely on the port shippers, the un-Portuguese likes of Cockburn, Croft, Dow, Graham, Sandeman, Taylor and Warre, based half a day's drive downstream in Oporto - or rather in lodges on the quayside of Vila Nova de Gaia across the river from it. Ever since the late 17th century, when British merchants scoured friendly Portugal for goods that would replace heavily taxed items from France, much of the commercial end of the port wine trade has been in British hands, which has made for an even more delicate relationship between growers and bottlers than in most wine regions.
The steep, rocky, necessarily terraced vineyards of the Douro were long since mapped according to the concentration of the wine they are able to produce, and grape payments decided accordingly. The best port country is almost 100 miles upstream of Oporto, well away from the rainy coast. Some very promising vineyards are not that far downstream of the point at which the Duero of Spain becomes the Douro of Portugal. The land is so inhospitable here, with only a dusting of topsoil, that many a vine sends it roots yards down into deep fissures in the schist, apparently the only possible route to the water necessary for growth.
It has taken the port producers much longer than most to understand, or even identify, the 80-plus vine varieties responsible for their amazingly concentrated, deep-coloured product. But then port, like sherry, champagne and madeira, is essentially a blended wine and many of the greatest ports I have ever tasted were made decades before the term 'varietal' was even coined. Touriga Nacional is generally regarded as the top quality port vine, supplemented with Tinta Amarela, Tinta Barroca, Touriga Franca, Tinta Cão and Tinta Roriz (the Tempranillo of Spain).
The aim of the port producer is to make a wine that is as deeply coloured and sweet as possible. To preserve the grapes' natural sweetness, grape spirit is added at quite an early point in the fermentation process to stun the yeasts, which means that as much colour as possible must be extracted before that point. The Douro valley is one of the very few wine regions where foot treading is still practised, to the delight of photographers and visitors from tamer wine regions, but machinery usually does the job and, as labour costs soar and the valley is gradually depopulated, much ingenuity has resulted in mechanical substituted for foot treading.
The most ordinary port goes into the shippers' basic blends, sometimes called wood ports as they are not expected to age in bottle (although many of them nowadays are aged in cement or stainless steel rather than barrels). A ruby port is a young port bottled after two or three years in bulk (in wood, cement or stainless steel). The great majority of port sold today, and certainly all the advertised brands, is this vigorous, juicy stuff. (If it carries the words late bottled vintage or LBV it will usually be a ruby from a single year bottled after four to six years' ageing.) Another term you may see on the label is reserve or reserva, used for better quality, or premium, ruby ports.
A cheap tawny is ruby's commercial cousin, from lesser vineyards or often made lighter and browner by blending in some white port, the result of applying port production techniques to the Douro's minority of white grapes. Real aged tawny owes its alluring light, shaded, jewel-like tawny colour to extended ageing in wood, for 10, 20, 30 or over 40 years according to the label. Some of my most hedonistic port-drinking experiences have been with 20 year-old ports, which taste as good served chilled in the heat of a Douro summer as they do next to the fireside in a British winter. Perhaps better. This is the style drunk most regularly by the port shippers. Superior non-British port producers include Ferreira, Niepoort (Dutch in origin), Quinta do Noval (now owned by French company AXA) and Quinta do Portal. Some shippers age a blend of tawny ports from a single vintage for many years in wood (at least seven) to produce colheita ports.
All these ports are matured in bulk before bottling rather than being expected to mature, like fine table wine, in the bottle in which you buy them.
The style of port traded in the auction room, however, and talked about most, is vintage, a long-lived wine that is relatively easy to produce because it is bottled after two or three years in wood and then left to mature in consumers' own cellars for decade after decade. Such wines, the produce of a single, superior year, generally about every third year depending on the quality of the wine and the state of the market, have to be made from the Douro Valley's finest, most concentrated, most tannic produce, to benefit from all those years in bottle (during which they develop a monstrous sediment, known as 'throwing a crust'). Such wines have to be decanted. These wines, called simply by the shipper's name and year, as in ‘Fonseca 2004’, represent only about one per cent of the Douro Valley's output. Poor man's vintage port is single quinta vintage port, which is the produce of a single wine farm, typically but not exclusively one owned by a shipper such as Graham's Quinta dos Malvedos, from a year not 'declared' as a vintage by that shipper. It offers a way of experiencing the style of vintage port without having to pay nearly so much or wait quite so long. These are some of the best buys in port.
Then there are some intermediate styles. Crusted port is a blend of different years bottled early in a specified year without filtration so that, like vintage port, it matures in bottle and has a heavy sediment from which it should be decanted.
Non-Portuguese port-style wines
Some other winemakers in climates as hot as the Douro Valley try their hand at making dark, sweet fortified wines in the image of port – with particular success in Australia and South Africa but also in California. Very few producers have any substantial plantings of the port vine varieties, however (although this is slowly changing). They are not generally allowed to use the word ‘port’ on the labels but any wine labelled Tawny is likely to be the product of long ageing in cask while a Ruby is likely to have been bottled relatively young. Perhaps the European wines most like port are Banyuls and Maury made in Roussillon, southern France.