Tokay grapes have a grand history in Europe. They are the Aszú grapes that the famous Hungarian sweet wine Tokaji is made from. As a young girl, my father gave me a few sips of this famous wine of my ancestors. It was said, a great uncle in Hungary made his fortune with these wines. Here is a little information on the famous and most excellent of them all. 
Tokaji Eszencia (Essence) is the most fabled and rarest of all. Eszencia is the first run juice of the Aszú grapes, which seeps from the press under the grapes own weight. The sugar content is extremely high, and the wine will ferment at an extremely slow rate, often over many years. Normally Essence will be used as a blending wine, although under exceptional circumstances, the best wine from the best grapes in a top vintage, will be released in its own right. These wines, will keep for many years (as will most Tokaji), and often command very high prices. Its legendary restorative properties are widely documented in Hungarian folk lore. It is why they call this The Wine Of Kings...

In the United States, however, sweet grape varieties were used to make very inexpensive dessert wines in California after prohibition. As a result, in this country, Tokay wine still to this day, has the reputation for being rot gut wine. There are a few wine makers in California that are starting to explore the possibilities of this wonderful and fat flavored wine.

All grapes are low in sodium, high in anti-oxidants, have food amounts of fiber, and are low in calories, with 70 per cup. Grapes do not get sweeter after picking, so color is the best indicator for ripeness and sweet flavor. Look for grapes that are plump and firmly attached to pliable stems. Avoid soft or wrinkled fruits.

Grapes are sold ripe and ready to eat. Refrigerate unwashed. They will keep will for up to 7 days at 38-40 degrees F. Just before service, rinse grapes with cool water. 

Here are excellent grape sites for information, recipes and more:

http://www.funkcity.demon.co.uk/tokaj2.htm

http://www.vins-lorentz.com/grapes.html