Why do you need to discuss Bourbon, its just another whiskey right? Well, yes, but there’s more to it than that. All Bourbons are whiskies, but not all whiskies are Bourbons. In the same way that to be called Scotch a whisky must meet certain criteria in order to call a product Straight Bourbon Whiskey a distiller must meet certain requirements. Wikipedia summed it up nicely so rather than regurgitate, I’ll just quote them.
- Bourbon must be made of a grain mixture that is at least 51% corn.
- Bourbon must be distilled to no more than 160 (U.S.) proof (80% alcohol by volume).
- Bourbon must be 100% natural (nothing other than water added to the mixture).
- Bourbon must be aged in new, charred oak barrels.
- Bourbon which meets the above requirements and has been aged for a minimum of two years, may (but is not required to) be called Straight Bourbon.
- Bourbon aged for a period less than four years must be labelled with the duration of its aging.
The first step in the Bourbon production process is the selection and processing of grains. As per the rules this grain mixture has to include at least 51% corn. The remainder is then made up of any of the other fermentable cereal grains, e.g. rye, wheat, barley, rice I suppose, etc. The grain mixture is one of the deciding factors in the final flavor of the Bourbon. As an example Bulleit Bourbon uses a high percentage of rye which gives the resulting spirit it’s characteristic spiciness. Since its this specific recipe of grains that makes each Bourbon unique it makes sense that the specifics are tightly guarded secrets. The distiller then takes the selected grains and mills them. Milling the grains maximizes the surface area allowing a more complete starch conversion, the next step in the process.
Once the grains have been milled water is added and heat is applied to the mash. The application of heat causes the starches in the grains to break down in to fermentable sugars that can then be consumed by the yeasts. Once the mash has been cooked a small portion of the previous mash is added to the new mash. The acid from this “sour mash” slows the growth of bacteria and creates the pH balance that the yeast requires for alcohol production. Which brings us to the fermentation itself. Depending on the chosen yeast this process can take anywhere from days to weeks but the result is the same a low alcohol content wash.
The wash is then transferred to a still where it will undergo distillation into a clear alcohol. When you buy a bottle of Everclear you are buying un-aged whiskey straight from the still. The maximum alcohol percentage that can be obtain through standard distillation is 94%. In order to go higher you have to employ a process called vaccuum distillation which is considerably more complicated, not to mention a story for another post.
At this point the un-aged Bourbon is transferred to new, charred oak barrels for aging. There are varying degrees of barrel char that can be utilized to produce specific characteristics. Once filled the barrels are moved to a barrel house for aging. As the temperature varies throughout the year the Bourbon is pulled in to the wood (as temperature increases) and pushed back out (as temperature decreases). This aging produces two distinct results. First the char on the barrel serves to filter the Bourbon to some degree. Second as the alcohol moves in and out of the wood it picks up color and flavor. There are lots of compounds in wood that help to give the Bourbon it’s unique final flavors.
Bourbons are aged for a minimum of two years and the sky seems to be the limit. Once aging is complete there are a few more options. One, the Bourbon can be bottled without dilution at what is called cask strength. Bourbons from the larger distilleries are typically blended to produce a consistent flavor and then diluted to the proof desired. Some distilleries however and choosing to bottle the product un-blended from single barrels. These single barrel Bourbons, such as Eagle Rare, one of my personal faves, will vary in flavor from barrel to barrel slightly depending on the barrel itself and where the barrel was aged. As such, you end up with a product that although similar will never be exactly the same. I like this as it gives cocktails a bit, although not too much, variability.
Well I hope this overview has been interesting for you. I’ve glossed over some subjects intentionally (e.g. the specifics of distillation) and I’ll be covering those in more detail later on. Some topics (e.g. barrel chars) I’ve skimmed over due to a lack of knowledge. As I know more about these I’ll be sure to write update posts. I’ll be visiting a couple distilleries this weekend in Kentucky and hope to find out a lot more interesting info and get some good pictures.