If aged tawny port is just for old fogies--as is sometimes suspected--then I'm applying for old fogie certification.

Two weeks of blissed-out tastings have left me convinced that aged tawny port is among the world's most wonderful and underappreciated drinks. Admittedly, it is not the stuff of current high fashion. Vintage port made a comeback of sorts in the 1990s, with increasing attention from wine collectors after great vintages in 1991, '94, '95 and '97. However, aged tawnies remain obscure even among devoted wine drinkers in America, which is mystifying in light of the fact that they are vastly easier to enjoy than vintage ports in both practical and sensory terms.

First, let's get the basics straight. All true port is wine fortified (by brandy) and sourced from the Duoro Valley in northern Portugal. Brandy serves both as a preservative and as an agent to arrest the fermentation process before yeasts can consume all the sugars from the grapes, and thus all ports are relatively sweet as well as strong.

The most basic divisions among port styles arise from different modes of aging. Vintage ports are aged briefly in wood after harvesting and vinification and then placed in bottles without filtration to mature for 20 or 30 years before becoming ready for optimal drinking. By contrast, true aged tawnies are blended from wines of different vintages that have matured in wooden casks. The component wines are frequently racked (transferred) from cask to cask to expose them to oxygen, which softens them in flavor and texture and leaves them with an amber-brown or tawny hue.

Once the component wines for an aged tawny are blended, filtered and bottled, they are ready for shipping and, once purchased, may be enjoyed immediately. For the great majority of wine drinkers who do not own temperature-controlled cellars, this is an incalculably great advantage over vintage ports. Another advantage is that aged tawnies will retain most of their quality for weeks and even a few months after opening, whereas vintage port should really be consumed on the day it is opened. This is because aged tawnies, unlike vintage ports, are effectively "inoculated" against oxygen by years of prior exposure.

Aged tawnies are also easier to use and notably more versatile. Unfiltered vintage ports will throw a heavy sediment in the bottle while maturing, requiring very careful handling and a fussy process of decanting. By contrast, aged tawnies will have shed most of their sediment while in casks, and the remainder is polished away during pre-bottling filtration. Moreover, while good vintage ports are impressively concentrated and robust, this very robustness has convinced generations of tasters that they should be reserved for cold-weather months. Aged tawnies, which are lighter in weight and much more delicate in flavor, can be enjoyed throughout the year (though a light chilling is advisable in warm months to keep them from appearing overly alcoholic).

Aged tawnies are bottled in four categories, indicated on labels as 10, 20, 30 and over 40 years old. These indications are somewhat misleading, as most bottlings are blends that include younger wines (that lend fruit and energy) as well as older ones (that lend softness and aromatic nuances). The only effective control on producers is that their bottlings must pass a tasting inspection (by the Instituto do Vinho do Porto) intended to assure that aged tawnies conform to the character expected from the age claimed on the label.

Not all tawnies are aged tawnies. If you spot a bottle merely labeled "Tawny Port," without one of the four age designations, it is almost impossible to know what you're getting. These wines show the tawny color of the real thing but usually not because they were patiently aged in wood. Rather, their light color typically results from use of underripe grapes, additions of white port or "baking" performed in overly warm cellars. Bulk tawnies are attractively cheap and sometimes fairly tasty, but the genuine article is worth the difference in price.

The best aged tawnies from my tastings are listed below in order of preference within categories. The 10-year-old bottlings are all excellent, and you need not pony up for the more expensive bottlings to get the idea. The 20-year-olds are often the most complete, but the complex delicacy of the 30s and over-40s can be astonishing. Aged tawnies are best enjoyed with walnuts or cashews and well-aged cheese.

Ten-Year-Old Aged Tawnies: Graham's ($30); Ramos Pinto Quinta da Ervamoira ($35); Rozes "Infanta Isabel" ($30); Romariz ($20); Fonseca ($30); Cockburn's ($26); Porto Feist ($20); Dow's ($25).

Twenty-Year-Old Aged Tawnies: Rozes ($50); Taylor Fladgate ($52); Porto Feist ($40); Royal Oporto ($56); Offley "Baron de Forrester" ($55); Graham's ($52); Noval ($60).

Thirty-Year-Old Tawnies: Porto Feist ($75).

Over-40-Year-Old Tawnies: Rozes ($140); Porto Feist ($120); Real Companhia Velha ($150).

Michael Franz will be answering questions live today at noon on washingtonpost.com