This drink is very popular in Vienna during autumn. It's a very young wine or rather a fermented grape juice. Sturm is only available during the harvest for about a month from late September to mid-October. The taste is fruity and refreshing.
The only drawback of Sturm is that it can't be stored for a long time. Because of the intense fermentation process, the bottle can simply explode if you seal it. Thus, the drink must be consumed within a few days or a bit longer if equipped with a special cap that lets the air through.