Watch for the time of year that you see the grape vines producing fruit. The aurore, for instance, is an early season variety, meaning that the grapes mature at the beginning of summer, while the vidal blanc is a late season crop that comes in between the end of September and beginning of October.
Note the colors of the grapes on the vine to help narrow down the possible varieties. For example, the cabernet sauvignon and venus grapes are black, but the delaware and moored grapes are red.
Pick open a grape to see if it contains seeds. Some varieties, such as canadice and reliance, produce seedless fruit.
Write down the location of the grape vine in question because certain varieties are found in certain areas, based on how well they adapt to the environment. The concord, as an example, is a common grape grown in the states east of the Rocky Mountains, while the steuben is ideal for Ohio.
Take a picture of the grape vine and bring the photo, along with your notes, to your county's agriculture extension office or a nearby nursery to get help with identifying the grape vine.