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Proprietary Wild Yeast

Guided by traditions other distillers have forgotten.

Not all yeast strains are created equal.

Before we can make our bourbon, we must ferment a mash of corn, wheat, and malted barley. Fermentation is carried out by a species of yeast called distiller’s yeast (scientific name is Saccharomyces cerevisiae). This species has the ability to metabolize sugars in the bourbon mash and produce ethanol as a by-product. Nowadays, most distilleries buy yeast that are manufactured in large quantities by a commercial lab. While consistency has improved with such commercial yeast, flavor diversity has suffered as distilleries are using the same, or very similar, strains.

Mashing

Yeast Lab Thumb

Yeast

The secret sauce.

What do we mean by a strain of distiller’s yeast? While all distillers use the same species of yeast (S. cerevisiae), there are many different strains within the species that will produce diverse flavors in the whiskey. This is due to the fact that while all distiller’s yeast produce ethanol as a by-product, there are a variety of other compounds (called congeners) produced – good and bad – that will contribute up to 25% of the whiskey’s flavors and aromas. Therefore, one strain of distiller’s yeast may produce a plethora of fruity esters, while another may ferment a very clean mash with very few congeners.

Think of it in the context of the humans: we are all apart of the same species – Homo sapiens. However, there is great diversity in our species. And even those humans that are similar in many ways (just as distiller’s yeast are similar in many ways), there will always be differences between each individual (or between each strain). This is the same case with the species S. cerevisiae. Only some S. cerevisiae are suitable for fermenting a mash, making them distiller’s yeast. But even with those that are distiller’s yeast, there are many individual strains that will produce different flavor congeners in a mash.

Therefore, a bourbon mash fermented with a unique, proprietary strain will possess flavors and aromas not produced by other strains. When the mash is distilled, the whiskey produced will maintain some of these unique notes that are solely due to the yeast strain used. Only a select number of distilleries still propagate a proprietary yeast strain, giving their whiskey a unique flavor as only their distillery uses that strain. Capturing and propagating a proprietary whiskey yeast strain is a craft that has largely been forgotten. In fact, it hasn’t been done since the end of prohibition when THE Jim Beam captured the yeast strain used by his distillery today.

Time to put on your lab coat.

Our Head Distiller, Rob Arnold, first collected a number of different samples (fruits, nuts, and soils) all from North Texas. Each individual sample was placed into a special, proprietary liquid media that encouraged the growth of alcohol tolerant yeast. After 3-10 days of growth, Rob isolated the yeast growing in the liquid media onto a solid media. Using this method, about 100 different yeast were isolated. With these isolates, Rob then had to determine which were of the S. cerevisiae species. Using the polymerase chain reaction (PCR) and DNA sequencing, he was able to identify 30 isolates within the original 100 that were S. cerevisiae. With these 30, he had to identify which, if any, were suitable for the fermentation of a bourbon mash. Employing small-scale fermentations, attenuation/flocculation analysis, and selection studies, Rob identified 11 of the 30 S. cerevisiae isolates that possessed the required ability to thrive and ferment in a bourbon mash. From here, it was all about flavor. Rob, Leonard, and Troy employed organoleptic analysis to determine which of the 11 strains possessed the desired flavor and aroma characteristics we wanted for our bourbon. Namely, we wanted a strain that produced a variety of fruity esters (banana, apple, pear) and floral acetals (rose), yet lacked any “earthy” notes (common with many wild yeast). We identified a strain from the 11 that fit perfectly with the desired profile. And as fate would have it, this strain was captured from a pecan tree nut in Glen Rose, Texas. With pecan being the state tree of Texas, we couldn’t be happier with our proprietary yeast strain. His scientific name is RHB-422, but we like to call him by his nickname – Brazos.

And that's just half the story.

Along with capturing our own proprietary yeast strain, F&R employs another technique that is used by very few distilleries – on-site yeast propagation. Unlike most distilleries who buy yeast in large quantities, we have to start from scratch to propagate enough yeast for 1000 gallons of mash. First, we start with a single colony of Brazos that has grown on solid media. Over the course of the week, we’ll propagate Brazos up from a single colony into 40 gallons of a thick yeast culture. The 40 gallons is then pitched into 1000 gallons of bourbon mash and allowed to ferment for 3-4 days. While this process is very labor intensive, it is a necessary step we must take in order to ferment with our own proprietary yeast.