Grape juice

Grape juice comes from crushing and blending grapes into liquid form. Sugars in grape juice allow it to be used for a sweetener.
In North America, the most common grape juice is purple. The juice is made from Concord grape. White grape juice is made from Niagara grapes. In California, Sultana grapes are sometimes used from the raisin or table grape to produce white juice.
Grape juice from concentrate means that excess water from the grapes was removed. This makes grape juice more concentrated. This allows grape juice to be compressed and frozen. It makes the packaging and transport easier. Water is then added to the juice before being sold. 
A major brand of American grape juice, Welch's, is made from Concord grapes, using an entire grape (pulp, skin and seeds). A small amount of citric acid is naturally found in grapes. It may be added for tart taste and antioxidant properties.