When becoming a Vegetarian there are some things that really do not cross your mind and which type of wine to drink probably falls into that category. When I first became a vegetarian in the 1980's I was a teenager and so wine was not really something that I thought about.As I got older and understood the wine making process better, having been on several vineyard tours, I suddenly began to realize that wine is actually made with parts of animals and so is not vegetarian. Don't panic you can get vegetarian wine so there is no need to stop your plans on becoming a vegetarian! Let me explain to you why wine is not generally made in a vegetarian way.
The clarification/fining process of wine uses various different types of animal body part these can be in the form of egg white, Gelatine, fish shells, fish oil, intestines, milk and even blood. The likelihood is that as an Ovo-Vegetarian, a Lacto-Vegetarian or an Ovo-Lacto-Vegetarian you could probably get away with drinking some regular wines but as a Vegan you certainly couldn't.
As the vineyards have become more aware of these issues and as new modern wine making methods have been brought in things have started to change and you can now purchase some very decent wines that are certified as vegetarian. You just need to be on the look out for them. Some retailers actually mark shelves or bottles as suitable for Vegetarians or Vegans. In my experience you find more Vegetarian wines than you do Vegan ones.
It can be a very confusing subject because vineyards use different processes each year depending on what the quality of the grapes are and how much work they need on them to make a good vintage. So one year you may see a wine marked as vegetarian/vegan and then the next year it isn't. That is not just a mistake on the bottle that means that they used something different in the process this year because the grapes needed it.
Some vineyards are certified as totally vegetarian or vegan for instance Fetzer in the USA all of their Whites/Blush wines are both Vegetarian and Vegan however their Reds are only Vegetarian. Of the Australian Vineyards all of Peter Lehmann's Reds are certified as Vegan and Vegetarian but the Whites are only certified as Vegetarian.
It's really just a matter of being vigilant when becoming a vegetarian, check bottles, check vineyard websites and also check for updates from the Vegetarian and Vegan Societies they keep up to date product lists.
