Sumitra Karki Naikap, Kathmandu Normally this is because of the agents that have been used to �fine� or clarify the wine, which can be animal derived products like isinglass (from fish) or gelatin (which can be derived from animal bones). There are alternative fining agents like PVPP, a synthetic agent, and Casein which is made from milk (so not suitable for vegans). Vegetarian-suitable wines normally carry that information on the back label.