Determining the alcohol content of a wine is simple and it also arms you with a fancy new wine term; legs. When you swish the wine in your glass around and let it settle, beads form around the inside of the glass and drip back into the wine forming lines. These drips are called the wine's legs. Legs tell you one thing and one thing only about the wine; the alcohol content. The thicker and the slower moving the legs are the more alcohol is in the wine.
Take for instance this $13.99 2007 El Burro Kickass Garnacha from Spain. This is my wine of choice when the objective is inebriation. It's pleasingly smooth almost creamy with gentle undertones of dark berries. It has a sweet front that rolls to sour/bitter but never harsh. Since it is very light on tannins it is a crowd pleaser that is easy to hold in ones mouth and contemplate. More to the point it has legs like a donkey, as its name suggests. A wine like this just might catch you off guard. As is displayed clearly on the label, this wine will kick your ass.
Before jumping right into a wine it is a good idea to check the legs. This gives you an idea of what to expect. It will help prevent you from getting caught off guard and it will prepare you for the flavor profile to come. If your goal is to get drunk, as I'm sure it sometimes is, then you want to know what the legs tell you.