Which wine is more dry, Cabernet Sauvignon or Merlot?

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Dear Dr. Vinny,
I overheard a bartender at a local winery state that "Merlot is the driest red wine." By no means am I an expert, but my experience is that Cabernet Sauvignon is almost universally drier. Like a fool, I challenged the young man, but he held his stance. Perhaps I am confusing acidity or body with the relative dryness of my wine? Please enlighten me!
—Bill, Marblehead, Ohio
Dear Bill,
Dryness has a couple of meanings in wine. The term is commonly used to refer to the absence of sweetness, and most table wines wines are technically dry in that they lack the residual sugar that makes dessert wines sweet. The typical Merlot has the same amount of residual sugar as the typical Cabernet—virtually none. Instead, I'm guessing both of you are referring to the feeling of dryness, which as you suggest is created by a wine's body: the balance of its acidity, weight, tannins and alcohol.
I agree with you that in general, Cabernet Sauvignon is a bigger, bolder wine that is much more likely to give you that puckery feeling from (in particular) its tannins than is Merlot. In fact, Merlot is known and loved for its supple tannins and easy-drinking profile. And while some Merlots might have higher levels of acidity than typical Cabernets, acidity makes your mouth water, not dry it out. So I'm on your side. While there are probably some examples of a Merlot feeling "dryer" than a Cabernet, generally Cabernet Sauvignons will leave more of a drying sensation than most Merlots.
—Dr. Vinny