Definition - What does Black Grapes mean?
The name "black grapes" is another name to describe red grapes. "Black" describes certain wine grape varieties which have deep red or almost black skins. The skins of these grapes may be a deep blue colored much like blueberries, or a deep purple or crimson like blackberries and mulberries. These dark pigments are also imparted into the wine.
WineFrog explains Black Grapes
There are many red wine grapes which can also be called "black grapes". These are the varieties which almost appear black.
Malbec, Zinfandel, Grenache, Cabernet Franc, Merlot, Tempranillo, Rondinella, Black Muscat, Pais and Alexander are a few examples of black grapes. Depending on where they are grown, they may be used to make single variety wines or as blending grapes. As the skins have such a deep hue, they have the ability to create dark and almost opaque wines. Colors can range from deep violet to dark crimson and inky purple. These wines are also often used as blending grapes as they can impart special fruit and spice characteristics to other wines, along with varying tannin structures.
Malbec and Zinfandel can add fruit and soften tannin structure of other wines as their skins are thin and do not make for heavily-tannic wines. Cabernet Franc and Tempranillo however, can impart tannin structure along with natural spice notes to other wines which are lacking structure.