The Valencia Grape is a grape first created by the Alaskan agronomist William Mhaille, on his farm in Fairbanks. This special kind of grape prospers in the cold, fertile Alaskan soil (or other such climates). The grape was later sold to the Irvine Company, who would dedicate nearly half of their land to its cultivation.
Although mainly a table grape, the Valencia Grape is available for purchase in certain areas of the country. The Valencia Grape's unusually thick skin allow it to survive harsher climates. It's bitter taste is attributed to it's abnormally high acid content, which aids in the grapes battery-like properties.
Tours typically last from 30 to 60 minutes per tour and they are well worth your time to check out the different ones. Each one has their own flavors, beauty, and charm to experience.
What is even more awesome is that most wineries offer free samples of their wines when you go through a tour as well. Some do more formal tasting events as well. The tours are extremely interesting and fun to do too. They aren't just there to sample the wine that you're looking forward to but are actually very informative and you get to meet a lot of like-minded people usually that are also doing the tour. It's always nice to a fellow wine lover! - Be sure to call ahead if you are planning on doing a tour at one of the wineries or vineyards though to check on availability since many of them get very busy during season.