What's the difference between a tawny Port and a Vintage Port?

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Dear Dr. Vinny,
What's the difference between a tawny Port and a Vintage Port?
—Wes P., Tulsa, Okla.
Dear Wes,
Tawny Ports become tawny-colored from the oxidation they experience during their long maturation in porous wooden casks—generally 10 years or more, up to 40 years in some cases. They have a mellow, nutty, slightly woody, dried fruit character. Vintage Ports remain in oak barrels for only two years before bottling, and so retain their deep red/purple color and sweet, ripe fruit flavors. Made entirely from grapes of a single declared vintage year, they are usually the richest and most powerful of Ports, and age exceptionally well in the bottle.
—Dr. Vinny