They are all roasted grains, but there are differences. Dark roasted grains can be roughly broken down into four categories: chocolate malt, black malt, "debittered" roast malt, and roasted barley. The degrees lovibond will tell you the approximate color of the malt.
- Chocolate Malts are pretty much what the name implies: generally they provide dark chocolate flavors with some supporting roast characters. Weyermann's Carafa (not carafa special) is simply their brand name for their chocolate malts and the I, II, III designation is their color. There are some minor difference between the three.
- Black Malt is more highly roasted than chocolate malt. Generally it is said to provide more coffee, roast, and some ashy flavors. It is generally used in smaller doses for color adjustment but can be used in larger percentages for stouts.
- Roasted barley is often roasted to a similar lovibond as black malt and provides many of the same flavors (some say it is slightly less ashy), the difference is that it is made out of unmalted barley. Roast barley is generally used in large amounts in stouts.
- "Debittered" roast malt is actually a separate category. These malts can span the color range from chocolate to black malt and have been processed in a way that removes a large amount of their roast character. The result is a malt that provides a lot of color with a relatively mild flavor. Weyermann's Carafa Special line and Blackprinz are debittered.
So, for color with less flavor, get a debittered (Blackprinz or Carafa Special malt).