It's really difficult to definitively determine a grape variety without genetic testing and I'm not sure if you could really have this done. The best thing to do is ask the seller if they planted them and what varieties they are. If it's simply two vines it's likely these are 'table' grapes as opposed to grapes that are typically grown for wine. The latter are much sweeter than table grapes and grapes like Pinot Noir tend to be smaller (more skin for the volume of the berry because it's the skins that provide the interesting characteristics of the grape.) If the grapes are sweet enough to eat, you can at least categorize them as green, red or black. If there are seeds that may also be a clue because many table grapes come in 'seedless' varieties. You could try taking in some samples of the vine and fruit into the Clackamas MG Clinic (that's the one closest to you) http://extension.oregonstate.edu/mg/metro/questions but you are welcome at any of the offices in the Metro area. If you think you have wine grapes, you could try taking them into a tasting room and ask if the winemaker can help you (this time of year might be difficult since it's such an early harvest.) If you like the grapes, then take the time to learn how to prune them. Grapes are very vigorous with little care but if left uncontrolled can become a nuisance. https://catalog.extension.oregonstate.edu/ec1639 is a great resource to get you started. Good luck!

Thank you Sara, very helpful! The previous owners don't really know the variety since they had not lived here very long and the vines were planted before they moved in. Both varieties are seedless, one seems to bear larger grapes and have a bluish-reddish tinge, the other has smaller grapes and is deep blue in tone. They are both fairly sweet, at least if I leave them on the vine long enough, and then the skins seem to slip off fairly easily, which someone says is a sign of a Concord grape. I moved in last summer, and had some at the end of the summer that I made grape jam from, but if they are wine grapes, I might be interested in getting them crushed and making a batch of wine. I will take them into the extension office for help. However, one more question -- the vines very much need some assistance in pruning and training them on lines, since the posts that they were attached to collapsed, and the whole thing is now a mess. I also don't really know how to prune them. Any suggestions about where I find a professional who can help me with the set-up, training and pruning?

I will tell you, if you have Concord, the grapes will taste just like Welches :) I have a seedless Concord in my yard but the vine is still pretty young and it's not in the best of location to get a lot of heat (Concords like it hot.) As far as a recommendation/referral, we really aren't allowed to provide professional referrals. However, http://www.corefruitinstitute.com offers classes locally and may be a good place to start. You can also inquire at your favorite independent garden supply/center for recommendations.