Which grapes make up the majority of California "jug" wines?

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Dear Dr. Vinny,
Which grapes make up the majority of California "jug" wines?
—Lou T., Steubenville, Ohio
Dear Lou,
It depends on the wine, but you'll find that most mass-produced wines are comprised of familiar wine grapes, though often in exotic blends. For example, I learned that Gallo's Hearty Burgundy is a blend of Syrah, Cabernet Sauvignon, Tempranillo, Petite Sirah, Teroldego and Zinfandel, while Carlo Rossi Burgundy is a blend of Cabernet Sauvignon, Merlot, Ruby Cabernet and Syrah.
—Dr. Vinny