Nothing quite gets the juices flowing of a bourbon connoisseur like bourbon aged 15 or more years. Expectations are raised. It's very easy to feel like you are about to be drinking something special when you see a number that's approaching the age of consent on a bottle of nice bourbon.
However, a lot of intermediate bourbon drinkers are shocked when an old bourbon tastes flat, yet harsh and mediocre or a young bourbon is full and smooth. This even leads some bourbon drinkers to the view that all bourbon is more or less the same and if you buy premium bourbon, you're just paying for marketing. It's a complex issue, so let's dive into the multiple facets:
First, let's consider how bourbon is aged. In order to be called straight bourbon, the bourbon must be made of at least 51% corn whiskey and aged in new (never used before) white oak barrels for at least two years (though if aged between 2 and 4 years, the maker must put exactly how many months old the bourbon is, which practically means almost all bourbon is aged at least four years, since very little bourbon that clearly says '2 years old' would sell). These barrels are also required to be 'fired' or 'charred', meaning that they are burnt on the inside. Legend has it that this was due to a fire at Elijah Craig's distillery, where they then tried to salvage some of the partially burnt barrels and found them to produce superior product. This account is almost certainly apocryphal. If you think about it, the insides of the barrels couldn't have become charred without first burning through the entire barrel first. No, the charred insides were almost certainly a method of sterilizing the barrels prior to usage, as a nice quick burn would kill any bacteria in the wood that might otherwise ruin the product. It was then a happy discovery that charring the insides of the barrels cause the sap of the white oak to caramelize on the outer surface of the inside of the barrel, just underneath the char. When the bourbon was then put in the barrel for aging, the bourbon would soak into the wood, and then would pull out much of the caramelized sugary white oak sap, giving bourbon its distinctive amber color and carmel/sweet flavor.
What caused the bourbon to go into the wood in the first place? Heat. When the storage temperature of the bourbon barrels rises, this causes the wood to expand and pull the bourbon in. When the temperature drops, it pushes the bourbon back out. These swings in temperature govern the aging process. If the bourbon merely sat in the barrel, without going into and out of the wood, virtually no aging would occur (unlike wine, grain alcohol itself doesn't continue to ferment once distillation is finished). Considering the drastic swings in temperature you find in Kentucky, this makes for relatively quick aging. Temperature swings play such an important role in the aging process that experienced tasters can often tell the difference between a bourbon stored in the middle of the rick house from a barrel stored on the outer edge, where temperature swings are more pronounced. Some distillers rotate their barrels throughout the rick house to give a more consistent bourbon, while some use these differences to create different varieties and levels of quality (for instance Booker's only comes from one small part of Jim Beam's rick houses).
Now, let's compare this to Scotch whiskey, which is aged in used barrels, in Scotland, which has much less extreme changes in temperature, due to the gulf stream, and is also just generally colder than Kentucky. In order to get the same level of effective aging, the Scotch is going to have to sit in the barrel for substantially longer in most cases. While the two processes are difficult to compare, you can roughly figure that aging 1 year in Kentucky is roughly equivalent to aging 1.5 in Scotland, in so far as how much the whiskey goes into and out of the barrel it is aging in. A single malt Scotch aged for just 6 years is quite rough in most circumstances (though not inherently bad), whereas many bourbons aged 6 years are extremely smooth.
Single malt Scotch is mostly where the 'aging craze' for whiskey started. Because scotch takes so long to age properly, a lot of inferior Scotch was legitimately rushed to market, since legally only 3 years of aging are required. Furthermore, older whiskey must be more expensive, because of three factors:1) The time value of money indicates that whiskey makers are putting up a substantial amount of capital up front for a return that is several years off. Simple interest would indicate that this would make it more expensive. 2) Storage space, the cost of barrels and other factors make simply storing the stuff expensive. Storing a barrel of 25 year old scotch for 25 years comes at an opportunity cost of not storing 3 barrels of 8 year old scotch. And finally, 3) Every year a percentage of what is in the barrel evaporates. This is euphemistically referred to as 'the angel's share'. Thus causing an aged barrel to produce less product than a younger barrel.
So, because many times older Scotch was genuinely better, and it was more expensive to produce, and thus demanded higher prices, it began to be associated as a luxury item. Gradually the age of the scotch was viewed as an indicator of worth, in and of itself. Even though some scotches required less aging for the same level of quality, they were aged longer, because older Scotches fetched higher prices. For example, many people feel that Balvenie 12 year old is actually inferior to the former Balvenie 10 year old, but the 10 year old was discontinued when the 12 year old was released (at a higher price).
Slowly, this age obsession creeped into the world of bourbon. For many years, bourbon was aged at 4 years and left at that. Some distillers would occasionally age a few barrels to blend in and give greater consistency between years, but for the most part all bourbon was aged about 4 years. Just enough to not be required to post the age, but not any longer. And this wasn't entirely detrimental. As we talked about above, Kentucky bourbon ages quickly. Especially if the rick houses are left with free ventilation to the outside air, as they typically were. However, a part of the issue was that following prohibition, bourbon makers simply were playing catchup, as virtually all stock of bourbon had been depleted. Thus, while bourbon did age faster, it was also pushed out the door as fast as could be in the years following prohibition, more or less all the way through the 80s.
In the 80's the popularity and reputation of bourbon began to fall, quite a bit. When people drank bourbon, they usually didn't even drink bourbon, they drank Jack Daniels (which is Tennessee Whiskey, though it's an open debate as to whether or not Tennessee Whiskey actually qualifies as bourbon, but since Jack Daniels has no desire to be labelled as bourbon, one that will never be tested). The bourbon industry needed a kick start for both sales, and reputation. They were getting killed on the low end by the growth of vodka as the cheap mixer of choice, especially as more females began to drink cocktails, and there essentially wasn't a high end bourbon on the market.
Along came Elmer T. Lee. Elmer T. Lee was the master distiller at Leestown Distilling, which was formerly ancient age. Lee knew from years of experience that certain barrels that he mixed into his blends were much, much better than others, or even the final blended product. He went to the distillery brass with the idea of creating a brand of bourbon that was selected, by him, from the very best barrels as he tasted them. Thus, Blanton's (and less well known Elmer T. Lee) were born. This was not only the founding of the single barrel movement, but more broadly the move in bourbon towards top shelf bourbon.
It is unarguable that the move towards creating a top shelf bourbon movement did in fact lead to substantially higher quality bourbon. However, it was when this movement mixed with the growing obsession with age in the scotch whiskey community that marketing began to take over.
Jim Beam has constantly, and respectfully, held the line that if done right, bourbon doesn't gain much anything from being aged over about 9 years. Booker Noe even going so far as to claim that some barrels don't gain a thing after 6 years. Yet, the age craze has somewhat taken off and just a couple of brands can be examined for it.
The biggest 'culprits' of the age craze are undoubtedly the Van Winkles. Makers of pappy Van Winkle 20 year old. Consider that for a second. 20 years old is old for scotch, but Kentucky bourbon? It's unthinkable in some ways. That would be the equivalent of something like a 30 year old scotch, which only a handful of those exist, and are considered to be extreme luxury items that often fetch in the thousands of dollars. However, one must ask, was 20 years of aging really what makes that bourbon so great? I've had Pappy Van Winkle 20, and while it's certainly good, I actually have slightly preferred Pappy 15 year old (and several other top shelf bourbons). The 20 years of aging is primarily a marketing ploy. That makes it the oldest bourbon out there that is semi-easily available (though Pappy Van Winkle can be hard to find, one must usually know a liquor store owner and have the store owner either save you a bottle or call you as soon as it comes in). In the case of most bourbon that is older than about 10 years old, it isn't so much the aging that makes the bourbon great, it is that it was simply great bourbon to start with. If Booker's was aged another 6 years, it would be excellent bourbon, but it likely wouldn't be substantially better than it is now. Elijah Craig 18 year old is among my favorite bourbons, but it's mostly quality control that puts it a small notch above it's younger (but still old) sibling, Elijah Craig 12 year old. In fact, Heaven Hill is known to actually slow down the aging process, by keeping the barrels that will become Elijah Craig under a more consistent temperature. The issue is slightly more complicated than this, but clearly a lot of the reason is so that they can slap the '18 year old' label on the bottle and sell it for $50, as opposed to $25.
In conclusion, my point is that bourbon should not be judged based on age. Sure, some old bourbons are fantastic. Elijah Craig 18 might be my favorite bourbon in the world. But the judgment should be based on taste, not the number on the label or the price tag on the shelf. As Jim Beam illustrates, some absolutely fantastic bourbons can be made in 6 years, if chosen properly. As always, your best bet is to just sample as much as you can and see what you like and try hard to not be biased by the label (if you can, blind tastings are always fun, and often revealing). Just because a bottle of Pappy Van Winkle 20 year old is that old and costs $150, doesn't mean it's better than a $50 bottle of Booker's or even a $30 bottle of Elmer T. Lee.