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North Carolina Brewery

Open Tanks and Free-Range Flavors

1 month ago, by Sierra Nevada
Posted in North Carolina Brewery

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There’s an old saying: brewers don’t make beer, yeast does. Without fermentation, there would be no beer. Much of what we as brewers do is work to keep yeast happy so it will produce the flavors we want in the finished beers. Now that we’re brewing on a consistent basis at our Mills River facility, healthy yeast is at the top of our minds.

Most of our fermentation cellar was completed nearly a year ago. The big cylindrical fermenters that we use for the bulk of our beers have proven to be as sound and reliable as any we’ve seen. This month, however, we installed a set of very special fermentation tanks—two brand new open fermenters.


Open fermenters—as the name suggests—are tanks with open tops that allow yeast to convert sugars into alcohol in an unrestrained environment. Conversely, the liquid in closed tanks creates pressure that can impact aroma and other characteristics. Most brewers around the world have adopted closed cylindrical fermentation tanks due to their ease of operation and cleaning, efficient use of space, and the ability to capture the natural CO2 produced during fermentation for reuse. For certain styles of beer, though, open fermentation makes all the difference.

Some beers just can’t be tamed by an ordinary closed tank and need the open-air freedom so yeast will produce the complex flavors and aromas a style requires. Beers like Kellerweis®, our Bavarian-style hefeweizen, rely on the intense clove and banana characteristics that come from the yeast. Other beers like Bigfoot®, our classic barleywine, need the open fermentation to allow the yeast to devour the massive amount of malt sugar and reach our target alcohol levels.


In 1980, our first brewhouse used recycled dairy tanks as open fermentation vessels. Ever since, we’ve insisted on doing a portion of our beers in open fermenters to encourage the yeast flavor. Our present-day Chico brewery has four 100-barrel square open fermenters. (One barrel is 31 US gallons.) These tanks have served us well over the years, but to be honest, they’re a pain in the neck from a brewer’s perspective. The tanks require someone to climb inside after each batch to scrub and sanitize every surface. In addition, oftentimes when fermentations build to fever pitch, yeasty froth will spill over the sides, making a sticky mess on both the tanks and the floor of the sealed room. Free-range yeast is tasty, but it sure isn’t easy. Check out this video to see for yourself:

Our new open fermenters in Mills River are state of the art. In fact, we’re the only brewery in the U.S. using them under license from an Austrian brewer. They were manufactured by Gresser in Regensburg, Germany, and shipped directly to us. The new vessels are round 200-barrel tanks with a built in clean-in-place (CIP) system, so no more climbing in. They also have a skimming chute along the top third which allows for easier top cropping—the harvesting of ale yeast from one tank and using it again in another. The new tanks will only make it easier for us to brew more of the labor-intensive open fermented beers we love to make.

Happy brewers make great wort, and happy yeast makes great beer. Hopefully, these new open fermenters will make life a little easier for the brewers, and the beer will make everything a little happier for the rest of us.