Step 6/15 - Fermentation: Yeast & Bacteria

We have finally reached one of the most exciting steps in spirits creation, fermentation. It is during this process that all the alcohol and most of the flavor of the rum is created. And the little creature that makes this all happen is the hero of todays lesson: Yeast!

While there are countless types of yeast the most common and hard working species is called Saccharomyces Cerevisiae (Latin for Sugar Eater). There are many different strains of this type of yeast though. What is often called Distillers yeast is a fast acting strain that can tolerate high levels of alcohol, while not creating much flavor. Bakers yeast and Brewers yeast, on the other hand, work slower but are often responsible for creation of more congeners.

Depending on each rum-producers focus, be it volume or flavor, many distilleries propagate their own strain of yeast that gives the output and flavor compounds that they are looking for. As long as the composition of the sugary wash stays the same, the output of these cultured yeast strains can be predictable to a certain point.

Yeast is also naturally occurring everywhere around us and this ‘wild’ yeast will often propagate in open fermentation tanks to some degree, along with airborne bacteria (most notably Lactobacillus). These microorganisms are in constant competition for food, in this case sugar. Yeast has two notable advantages in this competition though. Yeast is able to tolerate acidic and alcoholic environments that many bacteria struggle to cope with.

Next, we’ll get into the organic process of fermentation…stay tuned!