Cassis- A Story of Development on a Complex Barrel-Aged Sour

Cassis is a complex barrel-aged sour inspired by simple childhood memories of sour fruit in Germany.

In 2009, Derrick Morse was an avid home-brewer putting his recent food science college degree to work experimenting with sour beers in Boulder, Colorado. Sours had been around for centuries, but at that time, the style was not widely marketed to the mainstream beer consumers and was misunderstood, even among pioneering homebrewers. However, Derrick admired the style and genuinely enjoyed sour beers, especially from breweries like Cantillon, Brewfontaine.

With no literature on the style nor recipes to follow, Derrick spent $20 on a packet of lactobacillus and dove into experimentation. As a student of food science, he knew that lactobacillus and bacteria grow exponentially in high temperatures, but it was a cold winter in Colorado. So he creatively converted his garage into a mad scientist’s lab using a stainless-steel keg as a fermentor and placed it inside a water bath with aquarium heaters cranked up to 90 degrees.

Derrick explains, “I had this keg in a water bath with a water circulator pushing the water around, and two aquarium heaters keeping it warm. Every so often I would add more water since it evaporates. Friends would come over to brew and hang out and wondered what the hell I was doing with that weird rig.”

He described his first sour as interesting. “It was pretty good for my first sour. I had been home brewing for about two years at that point, drinking sours. I had a good understanding of the fundamentals and what it should taste like. It had some funk to it, and I was proud of it for being


my very first sour … and interestingly, a recipe that we eventually turned into Cassis. Though it was nothing compared to what we do today.”

In 2014, as Derrick Morse and Chad Frost were opening up Mantra Artisan Ales, Derrick was inspired by Rodenbach’s Alexander Grand Crew with cherries. Rodenbach’s version reminded Derrick of eating “Johannisbeeren”, or sour red currants, in Germany as a child. These childhood flavor memories inspired the name Cassis. In Belgian beer nomenclature, “Cassis” typically means the beer recipe includes currants. So Derrick named the sour beer Cassis based on this tradition. “It was pretty simple and obvious. It’s like calling an IPA an IPA. It’s like a style.”, says Derrick.

Derrick wanted the beer to be unique enough to spark conversation, and elegant enough to enjoy during the holidays. With this in mind, he visited breweries that specialized in barrel aging, to compile notes and outline specific goals for the Cassis recipe. Morse asked nearby Arrington Vineyards for some barrels to age the beer, and they were more than happy help. These barrels were very complex vessels, originally filled with Tennessee Whiskey, and then used to age Arrington Vinyard’s Antebellum series. The vanilla, wine, and bourbon flavor profiles of the barrels made them perfect for aging Mantra’s Flanders Red, Amour Rouge because Red Flanders already have cherry characteristics.

Morse explains the Cassis aging process, “It takes three isolated aging processes. We age our Flanders Red, Amour Rouge in Antebellum barrels. In a second barrel, we age Amour Rouge with currants. In a third barrel, we age Amour Rouge with cherries. Then we blend these three


barrels for the final recipe. It takes 8-12 months to get the perfect blend. Throughout the aging process, samples from each barrel are blended together and evaluated until it reaches its perfect maturation of flavor.”

The blending process is the most crucial part of creating Cassis, and the whole team participates. Everyone on the blending panel is assigned a multiplier based on their experience in tasting that determines their influence on the final blend. Higher numbers have a greater influence on the final flavor profile, but everyone has an influence. The blending process takes a lot of time, patience, and experience. Samples are taken from each barrel: the mother Amour Rouge beer, the Antebellum batch, a nine-month-old, three-month-old, and one-month-old Flanders, and previous batches. Each is poured into numbered glasses and team members rate the glasses on a flavor wheel. Initial blends are created based on the flavor profiles of each barrel, and the team pairs specific barrels together into the semi-final blends, which Derrick uses for his final blend.

The blending process makes every batch of Cassis unique. Morse shares, “In 2016, the Cassis blend was rich, jam-like, sweeter, and funky sour. It was well balanced between cherry and currants. The 2017 batch was more cherry forward because the customer base asked for it. Cassis 2018 will return to even balance, bringing back the strong currants flavor, with a jam-like, rich flavor profile. That’s where this beer shines.”

Mantra takes the time to make each batch unique and personal, following the personal mantra of quality over quantity. Every little detail of Cassis is an intentional work of art. Once the beer is blended, Cassis is treated like royalty in the beer world, with true elegance that speaks for itself.


Beautifully designed, embossed and foiled linen labels are applied by hand, and bottles are sealed with wax and stamped with the Mantra logo. Cassis is bottled in 750 mL bottles. When asked why he chose the bigger bottles, Derrick’s answer was simple: “I like to share … Something as beautiful as Cassis deserves to be shared with others. Cassis stands out in our spectrum of sours. We have no plans to change the recipe or process. Both are perfect, just as they are. Fans wait patiently all year for this beer to release because they know that art takes time. In the modern world, science enables us to mass produce the same thing over and over again, with precision and accuracy. But Cassis isn’t like that. It’s more art than pure science of brewing. We don’t set the deadline. It tells us when it’s ready … and when it does, it is a prized masterpiece that evokes wonder.”  

Cassis is distributed internationally. Stop by the Mantra Taproom to experience this story and masterpiece for yourself, and share it with others.