Bourbon explained - corn, new charred oak and sour mash
Bourbon is the American soul of whisky: sweet, vanilla-laden, caramel-rich, completely different from a Scottish single malt. Interestingly, what bourbon is is defined not by tradition but by strict American law. For a spirit to be called bourbon, it must meet a set of specific conditions, and each of them genuinely shapes the flavour. Understanding these rules explains where bourbon’s sweetness, intense vanilla and fast, deep colour come from. It is one of the most regulated, and at the same time most enjoyable, worlds of whisky.
The rules that make bourbon
Bourbon is a whiskey hedged in by law. The most important rules are these:
- Made in the USA. Bourbon can only be produced in the United States.
- At least 51 percent corn in the mash bill, the mix of grains. The rest is any other grains.
- Aged in a new, charred oak barrel. This is a key and very strict condition, more on it shortly.
- Strength limits. The spirit may not exceed 80 percent alcohol off the still, goes into the barrel below a certain threshold, and into the bottle at no less than 40 percent.
In addition, bourbon labelled straight must age for at least two years, and any younger than four years must carry an age statement on the label.
Corn, or where the sweetness comes from
The first pillar of flavour is corn. It makes up at least half the mash bill, and it gives bourbon its characteristic, soft sweetness and a full, round body. That is why bourbon is sweeter and gentler than dry, malty Scotch. The rest of the mash is usually rye or wheat, more on that shortly. I describe the whole whisky-making process in how whisky is made.
New charred oak, or where the vanilla and colour come from
The second pillar is the barrel, and here lies the biggest difference from Scotch. Bourbon must age in a barrel that is new and charred on the inside, which may not be reused for another batch. While Scotch whisky usually uses second-hand barrels, bourbon always gets fresh, heavily charred wood.
This has huge consequences for the flavour. New, charred oak gives intensely: vanilla, caramel, coconut, notes of spice and burnt crust, and it gives the whiskey a deep, amber colour very fast. Hence bourbon’s rich, sweet, woody profile. I cover where exactly these notes come from in where whisky flavours come from, and the role of the barrel in general in how the cask shapes whisky. Interestingly, these once-used bourbon barrels then travel to Scotland and Ireland, where whisky is matured in them.
Sour mash, or consistency
The label of a bourbon often carries the term sour mash. It is a method in which part of the fermented mash from the previous batch is added to the new one. It works much like a sourdough starter for bread: it lowers the pH, stabilises fermentation and ensures consistency of flavour between batches. It is less a flavour feature than a quality-control technique, used by most American distilleries.
Rye versus wheat
Since corn is at least half the mash bill, the rest makes a big difference. If the additional grain is rye, the bourbon is spicier, more peppery and more assertive. If wheat is used instead of rye, you get a so-called wheated bourbon, gentler, softer and sweeter, prized for its smoothness. It is one of the first things worth looking at when choosing a bourbon for your taste.
How to explore it
The best way to understand bourbon is to compare a high-rye version and a gentle wheated bourbon side by side. Spiciness versus soft sweetness is an immediate difference. In GustoNote you note the mash type, profile and your impressions of every bourbon, and after a few entries you will see whether you prefer the spicy style or the smooth and sweet one. It turns a general I like bourbon into a specific, conscious choice. You will find a full overview of world whisky in whisky around the world.