You say you have a Syrah that is not purple, and how do you know it’s Syrah? To address your second question first, I would say you really have to trust your supplier unless you want to spend a lot of money playing detective (more on that presently). The first step I would take is to look at the package and/or the packing slip that came with the grapes . . . I hope they say Syrah. If you still doubt the paperwork, certainly get in touch with your juice supplier and ask to see the paper trail from the lot of juice you received. Your supplier should have records of the entire process, from harvest to sale, showing the grapes being brought into the juicing plant from the field, being processed and packaged up into the containers you received and then the packing slip going to you. It might take a little time and phone calls on your part and a little annoyance on their part, but if they are on top of their customer service game they should be able to reassure you of the source.
What about DNA testing? Well, thanks largely to the work of Dr. Carole Meredith (famous for identifying the parentage of Zinfandel and Sauvignon Blanc, among other varietals), UC-Davis’ Foundation Plant Services actually does provide DNA grapevine identification services, though each sample costs $300 to perform and requires a leaf from the grapevine plant itself to be able to identify it. I know, so there you are again, having to trust your supplier that the juice you received actually comes from the grapevines they say it does. If you want to check it out, go to www.fpms.ucdavis.edu and click on “grapes.” I realize this is not practical; would you believe it’s something very few winemakers/grape-buyers in the wine industry do? I guess we trust the folks we do business with, plus we have a pretty good idea of when juice or must tastes and looks like, say, Pinot Noir, and when it does not.
Which brings me back to your first question. Before you read your supplier the riot act and sick your lawyers on them, you should know that Syrah grapes, juice and wine are not necessarily going to be a deep, dark purple every time. Even though Syrah is known as a higher-color varietal (in contrast to, say, Pinot Noir), what you have may very well be Syrah. I’ve made some Syrah from Lodi in the past that had a hue more red than purple. Sure, there was purple in there, but that particular clone on that particular rootstock in that particular place skewed a definite garnet hue rather than an amethyst purple, for example. The juice supplier might not appreciate getting a call from a customer accusing them of switching grape varietals on them, when due to site differences, vintage differences and many other things that happen along the supply chain, the color of a given lot of juice can vary.
Are you comparing your Syrah wine to other Syrah wines you’ve seen out in the marketplace or even seen in your buddies’ cellars? Winemaking treatments (such as cold soaking, maceration duration, how frequently the must is punched down) all make a huge difference in the amount of color extracted. One winemaker’s Syrah might look like ink and another’s can be a pink rosé — it all depends on the cellar treatment.
Are you comparing this batch of Syrah to previous batches you’ve made from this vendor’s “Syrah”? If so, and if it’s visibly different, your vendor might appreciate that phone call — it could alert them that folks are paying attention and they need to get their consistency back on track, especially if you see a brick-reddish-orange tinge (which could point to oxidation) or smell something funny (which could point to a microbial infection of the juice). If I were your supplier in that case, I’d appreciate a customer alerting me to what could be a quality control issue.