Muscat grapes are primarily used for wine making and occasionally raisin production. They are a large seeded golden yellow to rust grape with a high sugar content. They are used for German white wines that are somewhat fruity in nature and dessert wines. 

As with all grapes, Muscat 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  Muscat grapes with yield 2 cups.

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

A wine site with Muscat grapes:
http://www.wineday.com/opitz/index.html

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