Targets are often what drive brewers.
When contemplating a new beer, for example, you might start from a desired ABV, color, or level of bitterness. With a desired flavor profile in mind, you select your malt, hops, and yeast, and you tweak your water.
Occasionally, however, brewers will turn that convention on its head—instead of chasing numbers and flavors, they just let the process decide.
“We didn’t set out with a specific outcome in mind,” says Jake Sandenbergh, head brewer at Afro Caribbean Brewing in Cape Town, South Africa. “For this beer, it was all about the process, and we decided to let the process drive the flavor.”
The beer in question began with a grain bill of 97 percent Maris Otter malt. It ended up rich and viscous, near-black in color, with complex flavors of licorice, treacle toffee, Christmas cake, and a sprinkling of soy sauce. Clocking in at 17.5 percent ABV, the beer owes its ponderous depth and complexity to a process of heating and boiling stretched out over several days.
Swapping Stories
It began with two brewers trading stories over pints.
Nick Smith, founder and brewer at the award-winning Soul Barrel in the Cape Winelands, was reeling from a rough brew day—in mid-boil, a power outage had taken out his planned oatmeal stout. The wort sat in the kettle overnight; he eventually boiled it again, cooling and fermenting the beer to see how the extended kettle time would affect it.
Smith was recounting the story to Sandenbergh, who replied with his own tale of a boil that lasted longer than intended.
Sandenbergh’s first brewing job was in Johannesburg, just over a decade ago. The rudimentary brew kit at the small, startup nanobrewery turned brew days into marathon sessions, often carrying on into the evening. On one occasion, Sandenbergh had to head home mid-boil, leaving the brewery owner to finish the process. Arriving back at work the next day, however, he found the wort still sitting in the kettle—so, he fired it up to start the boil again.
“It turned out to be the best beer I’d ever made at that point,” Sandenbergh says. “We even took bottles to a local festival organizer, to ask if we could take a stand at his next event—and after sampling the beer, he accepted us.”
Smith’s story likewise ended up with a beer that surpassed expectations. So, the two hatched a plan.
“We began to talk scientifically about what was happening during this process,” says Smith, a graduate of the master brewer program at the University of California, Davis. “And then we thought, what if we really pushed it to the extreme? This is the kind of beer that definitely works best as a collab, since you’re exploring uncharted territory and trying new things. It really helps to have someone to bounce ideas around with.”
Much like the beer that would eventually follow, the idea marinated for a while—until one morning in September 2024, when the two locally respected brewers arrived at Afro Caribbean’s suburban brewpub to mash in on one of the most extreme beers either of them had attempted.
Their only real target: to achieve an evaporation rate of 50 percent. They set aside four days to boil the beer in various stages.
Boiling for Days
After mashing, Sandenbergh, Smith, and Afro Caribbean assistant brewer Jordan Hole began with a relatively standard two-hour boil, then they killed the heat.
They monitored the wort’s temperature: Whenever it dropped below 176°F (80°C), they’d fire up the gas burners and boil it again for another two or three hours, further developing the flavor and concentrating the wort. Maillard reactions took hold, gradually turning the wort from amber to brown to a tar-like black, as deeper and deeper levels of caramelized flavors developed.
In total, they actively boiled the wort for 20 hours. Sandenbergh estimates a further 20 hours of caramelization time as they repeatedly used the direct-fire brewhouse to reheat the wort to boiling point.
“That’s part of the reason we didn’t just do it for 20 hours straight,” Sandenbergh says. “The extra caramelization from reheating definitely added a lot more depth to the beer.”
“Plus, of course,” Smith says, “doing it this way was part of the original story—part of the reason we got here in the first place.”
A Challenging Fermentation
The original plan had been to conduct the boils over four days, assuming they’d achieved their target evaporation rate. However, issues in acquiring a suitable yeast strain added an extra two days to the process.
“We ordered a yeast that we thought would be capable of doing the job,” Sandenbergh says, “but the yeast didn’t arrive on time, so we ended up carrying on the boil for six days while waiting for the delivery.”
When the yeast did arrive, a new problem arose: “We oxygenated and pitched,” Sandenbergh says, “and nothing happened. Absolutely nothing.”
“We didn’t know how much complex sugar we had created,” Smith says. “Had we created a wort that was actually unfermentable? Did the yeast crap out because it was unhealthy or because there were no fermentable sugars left? Or did it crap out because of a lack of nutrients after such a lengthy boil?”
After a late scramble, they managed to buy a brick of Fermentis SafBrew DW-17, an enzyme-enriched yeast strain that’s suited to super-high-gravity wort. That strain is phenolic off-flavor positive (POF+), but that character wasn’t evident in the finished beer.
“We didn’t realize it was a POF+ yeast, but in the end, this didn’t affect the beer’s flavor,” Sandenbergh says. “Fermentation kicked off, and in just under two weeks we had a very clean beer finishing at 12° Plato [1.048].”
From Barrel to Bottle
They cold-conditioned the beer for a month before transporting it via keg to Soul Barrel, a 45-minute drive away. There it would spend the next year in a second-fill bourbon barrel. The brewers tasted the beer every few months to document its evolving flavor profile.
“It was very sweet at first,” Smith says, “like molasses, which of course goes through a similar process. Then, as it aged, it picked up a lot of dried-fruit character, and it has really mellowed out. I think it’ll probably age well in the bottle for a further 20 years or so.”
They named the beer Opus Aeternum—eternal work. They filled 500 bottles of it to release in South Africa just in time for Christmas 2025. They’re holding back some more bottles for aging, but that should be the end of it—they say they’re unlikely to repeat the experiment.
“I’m really happy with the beer, but I wouldn’t repeat this exact process,” Sandenbergh says. “But I would consider doing another beer with a 50 percent evaporation rate, to keep aside for blending. It has a very distinct, deep flavor, and I’d love to have 10 kegs sitting in the cold room to play around with.”
In the end, the beer is a testament to innovation—and to the resilience of South Africans in general, taking inspiration from a moment of adversity and transforming it into something rare and wonderful.
