Two of most the important components to understand when making great bourbon are the ingredients and the fermentation process. The grains of bourbon must be comprised of at least 51 percent corn, and normally also consist of malted barley and either rye or wheat. However, a of bourbon will show many grains can be used. But the real action in the bourbon making process happens during fermentation.
The Break-Down: Fermentation
The textbook definition of fermentation is: “a chemical process by which molecules such as glucose are broken down anaerobically.” Meaning that an agent like yeast is used to break down the sugars in the cooked mash and turn them into ethyl alcohol. This generates just enough heat to make the vat of fermenting liquid look as if it is boiling, even though it is seldom more than room temperature. This breakdown of sugars into alcohol is actually the beginning process of making beer, wine and other spirits.
The fermentation process begins once the cooked mash is cooled down to 25-30 degrees. The mash then moves into a fermenter – a large, cylindrical room made of metal or sometimes Cyprus wood. While adding the new mash to the fermenter, distilleries add some of the old mash to help control the PH level (or acidity) of the new mash. The cooking is a slow, low-heat process to preserve the character and flavor of the grains.
When fermenting, the liquid’s temperature is determined by the yeast. If the temperature is too low, fermentation could be slow or never reach its peak. If it’s too warm, you might get some off-flavors that will make the by-product taste off. Provided the temperature is just right, the fermentation process can take up to three to four days. The grains will start to sink to the bottom of the fermenting tank and yeast will bubble while it’s searching for sugars to turn into alcohol.
At the end of the fermentation process, the final liquid product that results is a basic beer, called Distiller’s Beer. It has about 10-15 percent alcohol content and is not unlike the type of beer that is filtered and refined to make the kinds of beers you find in restaurants, bars and stores around the world. The difference between bourbon and beer is bourbon makers aren’t done. At a distillery, once you have beer, you distill it!
Yeast (And no, not for your favorite bread)
Now you know yeast is one of the key components to making a great bourbon, but did you know there are hundreds of different types of yeast strains? For example, a traditional distillery could use a yeast that produces a malty, caramel flavor. Another could have a strain that turns up the intensity of the floral notes or even rye profile of a spirit.
Each distillery has its own yeast strain or several strains it uses. The yeast strains are a well-kept secret because that is where the flavor starts to form for good bourbon. Selecting yeast was always a simple process in years past. Today, few know what yeast strains are used in our favorite bourbons. Some distilleries use multiple types of yeast strains to achieve their bourbon’s flavors. For example, Four Roses Bourbon uses five different types of yeast strains to create certain aromas and flavors within its products.
There are different two types of yeast: Ale yeast (top-fermenting) and lager yeast (bottom-fermenting). Ale yeasts rises to the top of the fermenter during the fermentation process. This yeast will create a thick layer of yeast at the top of the mash bill in the beginning of fermentation process. Lager yeast ferments at the bottom of the fermenter. It does not reproduce as quickly as ale yeast, because it is made in cooler temperatures than its counterpart.
And for those of you who really want to get ahead of your friends on your bourbon trivia knowledge, here’s a little bonus knowledge for you: some popular categories of yeast go by simple letters like Q, K, F, O and V. For the record, Q has a slight fruit/spicy flavor and aroma, while K is rich in spiciness. F is for more herbal tastes and O is floral. Last but not least, V has an effect on the spirit of making it taste a bit creamier than other alcohols.
We can’t guarantee you’ll be correct in identifying a particular yeast category if you detect a bit of spice or floral notes in your next bourbon tasting, but we’re sure your friends will be impressed.
Learn more about the fermentation process and the power of yeast in our section on How Bourbon is Made