The two major styles of Port that require decanting are:
A. Vintage Port and Tawny Port
B. Vintage Port and Single-Quinta Vintage Port
C. Ruby Port and Late-Bottled Vintage Port
D. All Ports require decanting
The only Ports that need decanting are those that throw a sediment. These include two of the major styles: Vintage Port and Single-Quinta Vintage Port. None of the other major styles (Tawny, Reserve, or Late-Vintage Bottled) throw a sufficient sediment. Vintage Port is made only in exceptional years when Port shippers “declare” a vintage. A vintage Port may come from grapes from several quintas (renowned vineyard estates) as well as grapes grown by dozens of small, individual grape growers. Vintage Ports are first aged just two years in barrel, to round off their powerful edges. Then they are aged reductively (with only the tiniest amount of oxygen) for a long time in the bottle. A decade’s worth of aging is standard, and several decades used to be fairly common. To maintain the intensity, balance, and richness of vintage Port, it is neither fined nor filtered. This, coupled with the fact that Port grapes have thick skins and a lot of tannin, means that vintage Port throws a great deal of sediment, and always needs to be decanted.
In the years a shipper chooses not to declare a year as vintage quality, the grapes that would have gone into vintage Port are often used to make a Single-Quinta Vintage Port. The idea behind these Ports is that the very best vineyard estates are often located in special mesoclimates that allow exceptional wines to be made even in years when the vintage as a whole may not be declared. Apart from blending, Single-Quinta Vintage Ports are made in the same manner as Vintage Ports, so that the wine must eventually be decanted.