We all know that the barrel supplies much of the viscosity, sweetness, creaminess, and flavor of bourbon (but not all), and that the spice and the alcohol aid in keeping the sweetness from becoming cloying (c.f. the role of hops to offset the sweetness of malt in beer).
BUT, rarely do we see anything about the role of the tannins from the barrel in discussions of bourbon, except when they get out of hand and tend toward the too dry or the too bitter.
Come I now, to correct this oversight. I make no claims for my bourbon expertise, beyond having sampled and experimented with many whiskies, or for my palate, beyond being able to detect (methinks) a moderate number of flavors and qualities.
Still, just as I find some sweetness deriving from rye grain (am I the exception here?), I think tannins add length and subtlety to bourbons, as long as they are kept in proper proportions. That is why, for my palate, the most interesting bourbons are those whose age is 10+ years. Please, please understand that I am trying to take anything away from what most experts think is the sweet spot for bourbons......... about 8 or so years of age. Taste, is, as we are repeated told, a subjective thing....... and so it is, to a point. Were taste truly totally subjective, we would have nothing about which to contend, and no common ground around which to dispute.
Yes, tannins add a dryness and can add bitterness, but methinks tannins are best understood as moderating other tastes (particularly sweetness) and carrying them through the palate into the finish. Maker's Mark is a favorite bourbon for many folks, and it is a very good bourbon............. BUT, to my palate, it has no length and not all that much complexity. Sooo, Maker's Mark offered Maker's 46.......... a much superior, in my opiniion, bourbon because it has a decent finish and more complexity than regular Maker's. They did so by exposing the bourbon to more wood surface and thereby increasing the tannins. I think this was a bold and innovative move by Maker's, and I applaud it.
Many would disagree with me about the importance of tannins, and find them a fault in bourbon, and many find age in bourbons (wherein most tannins reveal themselves) to be a very poor guide to bourbon quality. I agree that there is no sure relationship twixt age in bourbon and quality, but there is, in my opinion, a significant one. And, unfortunately, that relationship is often exploited by bourbon producers... in much the same way that you or I would exploit it were we in their position.
I buy, and enjoy, many of the whiskies (corn, rye, and malt) produced by the craft distillers They generally are not price competitive, nor are they usually (in my opinion) subtle, delicate, or as complex as older whiskies. And they are prone to try various methods to achieve some subtlety and complexity, e.g. smaller barrels or wood chips to accelerate 'aging'. Among these, some of these efforts work, some do not...... and some, to their credit, harken back to the essential grain flavors.
Without having a secure grounding in the history of spirits aged in wood, I venture to say that aging in wood, which probably owes most to Cognac, is never just about extracting sugars and sweetness from the wood (surely it does not take 30+ years for Cognac to get the good sweet from wood). As with the best wines (to my knowledge) tannins play a central, but often unacknowledged, role in those that are considered 'exceptional' by knowledgeable drinkers.
Understand please, that by invoking the term 'knowledgeable drinker', I intend no particular moral credit to accrue to those personages. I have not the least doubt that many 'knowledgeable drinkers' were first rate Sons of Bitches, nor that many who could not wax eloquent about their drap of drink were, and are, first rate human beings.
I do this kind of exercise because I love whiskey and want to know why......... if it is of no interest to you, so be it, but, as I have said in the past, this is a site for Bourbon Enthusiasts............ and, I am one of those!