Concord produces medium-sized clusters bearing large,
blue-black berries. It is typical of the American V. labrusca-derived grapes in having a tough skin that separates readily from the pulpy flesh (slipskin). The pronounced fruity, or" foxy" "labrusca", or American flavor of Concord makes it a desirable dessert grape. Skin cracking and excessive
postharvest shelling, however, as well as the presence of seeds, limit its use for this purpose. It is the most important variety for sweet juice, jelly, and preserves, and it is also used in quantity for wine production and fresh market sales. 

As with all grapes,  Concords  are low in sodium, high in anti-oxidants, have food amounts of fiber, and are low in calories, with 60 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  grapes with yield 3 cups.

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

http://www.concordgrape.org/

http://food.homearts.com/food/cookings/calen/a7cala46.htm

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