The Build Up (and Break Down) of Fermentation at Black Frost

Fermentation is everything.

When you visit Black Frost, the first thing you will see is our fermentation and distillation area. While the stills typically get all the attention in the distillery, without the fermenters, you would have nothing to distill. We are particularly proud of our fermenters, and as you will learn, there is a lot more to them than meets the eye.

From the very beginning, we planned to have open top wooden fermentation tanks here at Black Frost. Beyond that, we decided to go with a very specific shape- tanks that are wider than they are tall. The decision to go with this style of fermenter was heavily influenced by my background in brewing. After I graduated from brewing school, I had the fortunate opportunity to intern at a classmate’s brewery in Austria. Their beers were fermented exclusively in open top fermenters. Having the chance to work with them and taste the difference it made in the quality of their beers is something that has always stuck with me. Yeast produces CO2 during fermentation and allowing that C02 to escape freely and effortlessly during fermentation, vs through a small pipe in an enclosed tank, helps to minimize stress on the yeast. Going with a fermentation tank that is wider than it is tall also helps to minimize stress on yeast. This combination of size and shape encourage the yeast to produce more esters during fermentation. Esters are the pleasant, fruity notes you smell in your whiskey, and something we want to be a big part of our flavor profile. Esters can be produced by yeast alone, but also through a chemical reaction of an acid and an alcohol called esterification (…try saying that three times fast!) This is the reason why we chose wood instead of stainless steel for our fermenters. The surface of wood is very rough, and nearly impossible to clean. Over time, bacteria will build up inside the wood, creating a unique microbiome that will produce an abundance of acids during fermentation to be esterified. 

The fermenters at Black Frost have a rather interesting past of their own. Built in 1989 entirely from French Oak, they spent their first 28 years making wine in California. They were then dissembled and rebuilt at a brewery in Illinois for a project that never got off the ground. After they sat empty for four years, I received a very serendipitous phone call from a friend who asked me if I was interested in them. Although we had planned on building new tanks, they were the exact size we were looking for. I jumped at the opportunity, spent 3 days disassembling the tanks, and then had them shipped to the distillery. It would be almost a year before I was able to start working on them. The first step was cutting the tops of the tanks off to transform them from storage vessels into fermenters. Then came the fun part- putting them back together one stave at a time. The floorboards are laid down first, placing a reed in-between each stave to help retain water during rehydration. From there it was putting the walls back together. It’s a bit like building a house of cards, especially because the wood was so dry, and I was rebuilding them differently than what they were originally intended for. Contrary to popular belief, I am by no means a master cooper, so I was figuring it out as I went along. There is no nails or glue - only wooden dowels between each stave, and then metal hoops around the outside holding it all together. As the wood absorbs water, it expands and eventually becomes watertight entirely through pressure. 

Soon, we will begin putting these fermenters to use making whiskey and rum. We’re excited have you along for the journey, and will continue sharing the science behind the flavors and the process we’re using to create our one of their kind, northern terroir inspired liquors. Stay tuned. 

- Jace Marti

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Farm to Barrel: Bringing the Flavors of the Northern Terroir to Whiskey

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The Beginning.