When Jeremy Marshall, Head Brewer for Lagunitas, accidentally ordered three pallets of oat malt instead of three bags, the unexpected surplus sparked an idea. Rather than ship it back, which would have been cost-prohibitive, Lagunitas leaned into the challenge and decided to push the boundaries of brewing.
Enter Old Caz Beer, a Sonoma County brewery known for its creative and scrappy approach to beer. The two breweries teamed up for the recent SF Beer Week to create Cazunitas, a 100% oat-brewed IPA that, as the company put it in a press release, “shouldn’t exist — yet, against all odds, it does.”
Using only oat malt presented significant technical challenges, especially in lautering, a process that typically benefits from the structure provided by barley husks.
“Mark Hughes called it ‘nervous brewing’ and literally stood there and watched, waiting for mayhem,” Marshall said. “At the start of the brew, we had straight-up oat milk during wort recirculation! But then, like a thunderstorm passing over, it cleared up, and we had the inklings of what could be a beer — maybe even a new style.”
The first brew was stripped down to the basics, or as Marshall described it, “naked.” No mash salts, no pH adjustments, no enzymes — just oats. The team later introduced beta-glucanase, an enzyme used to break down complex sugars and improve fluidity.
“It performed better in the runoff than we expected, likely due to the high husk content of the oats, the low mash-in temperature, and enzyme addition,” Marshall said.
Unlike barley, oats have lower extract potential, meaning they yield less sugar for fermentation.
“Oats contain about 60% extract to barley’s 80%, so not only are they more expensive, but you have to use even more of them,” Marshall said.
The result? A beer that was more fermentable than expected.
“It just kept going and going, getting really dry. Tom [Edwards of Old Caz] was even worried about losing the balance. We told him to chill; it’s probably fine,” Marshall added.
Despite the unusual grist composition, the team decided against adding rice hulls to aid runoff.
“I don’t like them. They are messy and completely unnecessary,” Marshall said. “Oat malt has tons of husk.”
To navigate the gelatinization temperature of oats, the brewers developed a custom mash schedule.
“We mashed in at 44°C, raised to 55°C for 20-30 minutes for gelat, then raised to 58°C for runoff,” Marshall said. “Tom at Caz had it way harder because he doesn’t have the ability to run a temperature-programmed mash. We forced him to mash in super thick and do a kind of decoction.
“German brewmasters would curse me for calling it that, but it’s accurate.”
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The brewhouse efficiency took a hit, down about 25% from normal. The oat malt clogged the milling and grain handling systems when dry, then clogged transfer pipes when wet.
“Bryan (Donaldson) had to take apart a bunch of things and dig oat schalrf out of them while saying very loudly, ‘This is freakin’ oatrageous!’” Marshall recalled.
Still, Cazunitas gives a look into what can happen when you embrace the unexpected.
“This 100% oat-brewed experiment pays homage to our joint unconventional, fun, and innovative roots while giving a nod to our beautiful backyard of Sonoma County,” Marshall said. “And most importantly, not taking ourselves too seriously in the process.”
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