Wine is made from grapes, what's not vegetarian about that? In fact, animal products are used in the production of some wines.

 

Some winemakers use products derived from animal products to clarify the wine. A clarifying agent is added to remove proteins, yeast and other organic particles from the wine. As the active ingredient sinks, the contaminating particles are bound to it and washed out. The active ingredient is completely removed from the wine.

Animal substances used to clarify wine include gelatine, fish glue, casein and egg white. In some countries, bovine blood is occasionally used as a clarifying agent, although this is not permitted in the USA and Europe.
Casein and egg white are suitable for vegetarians, as they are obtained from egg and milk protein respectively, but not for vegans.

Vegetarian wines use bentonite, a mineral that is suitable for clarifying the wine, as an alternative active ingredient. There are also winemakers who allow the particles in the wine to sink naturally. This is just as effective, but more time-consuming.

As the active ingredient is completely removed from the liquid, winemakers do not have to state on the label which one they have used in the production process. Unfiltered wines, in which the particles have naturally settled, usually state this on the label because many wine connoisseurs prefer unfiltered wines.

Kosher wines use fish glue for clarification, which is not taken from sturgeon, because sturgeon is not considered kosher.