Little did he know what a slug fest asking that question can ignite. Since the micro-distiller age has dawned, much of the discussion on that question has been bullshit. This is an attempt to answer it honestly and equitably in the context of our times.
Most micro-distillers are faced with a dilemma. They rarely have enough capital, or patience, to put their product away for four years or more, so they try to come up with ways to make it drinkable at a younger age. If they tell you it's the product they want to make and not a financial decision, they are lying. If it's not money it's petulance. They just don't want to wait so long.
So we have small barrels, spirals, vacuum pumps, finishes, and rationales that remind one of the fable, "The Emperor's New Clothes." And we have a lot of very hot, harsh, white-doggy spirits.
But it's not all bullshit. Some producers have tried to solve the problem thoughtfully and stylistically, remembering that the first rule of beverage making is: "Don't try to pass off disgusting crap with a good story. Make something that, first and foremost, tastes good."
At this, some have been more successful than others, but no product has been completely satisfying. Still, it's a worthy quest and none of them have been at it for very long. They will get better. They probably hurt themselves when they call their product 'bourbon' or 'rye whiskey,' if the taste and character one usually associates with those styles are nowhere to be found.
Which brings us back to the original question: "How Long Does It Take to Make Good Bourbon?" Let's assume that by "good bourbon," the questioner means the drink most whiskey drinkers would recognize as "good bourbon." The wisdom of the families and companies who have been making bourbon for a long time--several centuries in some cases--is that in a climate similar to Kentucky, it takes a minimum of four years in new charred wood to make something you would like to drink.
There are a few three-year-olds out there from the major distilleries, and they pretty much prove the point.
And four years, in itself, is a short cut compared to the minimum ten to twelve years it takes in chilly Scotland or Ireland. The short cut Americans came up with is the new, charred oak barrel, emphasis on 'new.' That innovation was a different and shorter route to deliciousness, but it made a different style of whiskey, as did our use of corn and rye instead of barley malt. We call that style 'bourbon.' 'Tennessee whiskey' is what Tennessee producers call the same style.
In a way, American rye whiskey should be called 'rye bourbon,' since it is whiskey made in the bourbon style but with rye as the dominant grain rather than corn. Wheat whiskey could probably be called 'wheat bourbon,' using the same logic. That's because, under U.S. rules, mash bill is the only variable. All require the new, charred oak barrel.
But that's just by way of making a point. No one is proposing that nomenclature.
If you're worried about all of those used-once barrels going into land fills, they don't. They go to Scotland, Ireland, Canada, Mexico, Puerto Rico, Jamaica. You get the idea.
Looked at in that broad historical context, you can say today's micro-distillers are working on their own new style of whiskey, something that's tasty after less than four years in wood, and frequently much less. It's a work in progress. Some are trying to do it the old-fashioned way, although few have anything on the market that's more than two years old.
Eventually, though, they will. And through experimentation the younger products will get better too. Either that, or there will be a lot of second-hand stills for sale.
So, again, back to the question. Traditionally, in Kentucky and Tennessee, the consensus is that four years is the minimum, five to six is better, eight to ten is optimum, and beyond ten you're again getting into a different, wood-heavy style, which is risky but can be superb.