But for a whiskey to be called bourbon, it must Follow very specific rules. For one, it needs to be made in the United States or a U.S. territory — although nearly all products are made in Kentucky. Other rules have more to do with the steps in making it—the amount of corn in the grain mix, the aging process, and the alcohol content.
I am a bourbon researcher and professor of chemistry He teaches fermentation classes and I’m a bourbon connoisseur myself.this complex science What’s behind this aromatic drink reveals why there are so many different varieties of bourbon despite the strict regulations surrounding its production.
Mix and match bill
All whiskeys have what is called a mash bill. Mash bill refers to the recipe of grains that form the basis of a spirit’s flavor.To be classified as bourbon, the spirit’s mash must have At least 51% corn – Corn gives it its characteristic sweet taste.
Almost all bourbon whiskey contains barley malt, which provides a nutty, smoky flavor and provides enzymes, convert starch into sugar later in the production process.
Also used by many distilleries rye and wheat Flavor their bourbon. Rye makes the bourbon spicy, while wheat creates a softer, sweeter flavor.Others may use Grains like rice or quinoa – But each grain chosen, and the amount of each grain, affects the final flavor.
Chemical properties of yeast
Once the stills have ground the grains in the mash and mixed it with hot water, they add yeast to the mash. This process is called “yeast pitching.”Yeast consumes sugar during fermentation and produces ethanol and carbon dioxide as by-products – this is how yeast works bourbon turns into alcohol.
The fermented mash is now called “beer”. While the product is similar in structure and flavor to the beer you buy in a six-pack, it still has a long way to go before it reaches its final form.
In addition to alcohol and carbon dioxide, yeast fermentation produces other by-products, including flavor compounds called congeners. Homologues can be esters that produce fruity or floral aromas or complex alcohols that are rich and aromatic.
The longer the fermentation takes, the longer it takes for the yeast to produce more Delicious by-product, which enhances the complexity of the spirit’s final flavor.Different yeasts produce different numbers of homologues.
Separate fermentation products
During the distillation process, the still separates the alcohol and congeners from the fermented grain mash, creating a liquid spirit.For this they use Pot or column still, respectively a cauldron or column, usually made at least partly of copper. These stills heat beer and anything with a boiling point below 350 degrees Fahrenheit (176 degrees Celsius) to create steam.
this static type This can affect the final flavor of the drink because pot stills generally cannot separate like substances as precisely as column stills.Pot stills produce spirits that often contain more ingredients complex mixture of homologues.
The desired vapor leaving the still is condensed back into liquid form and the product is distillate.
Different compounds have different boiling points, so a distiller can separate different chemicals by collecting distillate at different temperatures. So, in the case of a pot still, when the kettle is heated, the chemicals with lower boiling points are collected first.As the kettle heats further, chemicals with higher boiling points evaporate and are Concentrate and collect.
At the end of the distillation process in a pot still, the distillate has been separated divided into several fractions.One of these fractions is called “heart”,” contains primarily ethanol and water, but also smaller amounts of congeners that play an important role in the final flavor of the product.
The Alchemy of Time and Wood
After distillation, the “heart” part (clear and water-like) is put into charred oak barrels for the aging process.Here, the bourbon interacts with the chemicals in the barrels, approx. 70% of the final flavor of bourbon determined by this step. Bourbon takes on an amber color as it ages.
Bourbon can be aged in barrels for several years. In the summer, when temperatures are hot, the distillate can pass through the char layer inside the barrel.Charred wood acts like a filter filter out Some of the chemicals before the distillate seeps into the wood. These chemicals bind to the charred layer and are not released, a bit like a water filter.
There is a “red line” underneath the charred layer of the barrel, which is the layer of oak that was toasted during the charring process of making the barrel.baking process Break down starch and other polymerscalled lignin and tannins, found in oak wood.
When the distillate penetrates into the red line layer, Dissolved sugars There are also lignin by-products and tannins in the barrel.
During the cold winter months, the distillate flows back into the barrel, but it takes away the sugars, tannins, and lignin byproducts of the wood, enhancing the flavor. If you take apart your bourbon after aging it, you can see “solvent line,” which shows how deeply the distillate has penetrated into the wood. The type of oak barrel, the size of the barrel and the degree of charring can all have a profound impact on the final flavour.
For most wineries, the barrels are stored in large buildings rickhouses. The ethanol and water in the distillate evaporate from the barrel, and the humidity in that part of the warehouse plays a big role.
Lower humidity generally results in a bourbon that is more durable because more water leaves the barrel than ethanol. Additionally, air enters the barrel, and the oxygen in the air reacts with some of the chemicals in the bourbon to create new flavor chemicals.These reactions will often Soften the flavor of the final product.
have Thousands of bottles of bourbon On the market, they can be distinguished by their unique flavor and aroma. The diversity of brands reflects the many choices made by winemakers on mash bills, fermentation and distillation conditions, and aging processes. No two glasses of bourbon are exactly the same.
Michael W. Crowder, Professor of Chemistry and Biochemistry, University of Miami
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