Black Corinth is sometimes called Champagne grapes, however this is a misnomer. The Black Corinth is a tiny sized grape that is seedless, firm skinned, crunchy variety of  grape. It has super sweet flavor and when ripe is a dark red/black color. The bunches should be long and full of grapes. This type of grape is very popular in the  United States and is used extensively in foodservice. It is popular with caterers, as it is a visually attractive grape that is used with great effect on fruit mirrors and fruit presentations. When dried, Black Corinth grapes are called  Black Currants or Zante Currants however, it is not a true currant.

As with all grapes, Black Corinth 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. 

One pound of seedless grapes with yield 3 cups.

Here are three in-depth and excellent grape sites for information, recipes and more:

http://www.tablegrape.com/rev99/index.htm

http://www.dole5aday.com/encyclopedia/Grapes/grapes_types.html