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Not So Fast: Tips on Brewing Better “Quick Sour” Beers

Kettle acidification has become an important technique in the craft brewer’s bag of tricks. Here’s some advice from a few of the best in the business on how to get greater consistency and depth of flavor when deploying lactic acid–producing bacteria.

Don Tse Mar 31, 2023 - 14 min read

Not So Fast: Tips on Brewing Better “Quick Sour” Beers Primary Image

Photo: Courtesy Jeff Young

The great advantage of “kettle souring” has always been that it’s relatively fast and easy. Yet the flavor results can be as simple—or as complex—as the thought and process behind them.

For example, you can simply add food-grade lactic acid for a balancing tartness—the quickest sort of quick-souring—but that’s unlikely to add alluring depth. On the other hand, by investing a little more time and effort into your lactic acidification, you can elevate your “quick sour” beers with more character and flavor.

Here are tips from a few of the most accomplished pros in the trade.

Help the Microbes You Want, Hinder Those You Don’t.

To get the best from your Lactobacillus culture, you need to create an ideal environment for it.


That’s why Michael Tonsmeire, cofounder of Sapwood Cellars and author of American Sour Beers, recommends pre-acidifying your wort to between 4.4 and 4.5 pH. That will inhibit the growth of pathogenic bacteria and minimize the risk of off-flavors. Using a bit of lactic acid to get your wort into that range between mashing and pitching Lacto will help ensure a cleaner beer in the end.

Whatever vessel you’re using for acidification, whether kettle or tank, Tonsmeire is a proponent of using CO2 to purge it of oxygen. While some argue that purging isn’t necessary—and others may want a restrained touch of acetic acid as part of their profile, depending on the Lacto strain—purging can prevent the growth of unwanted aerobic microbes. Taking this a step further, because a kettle is typically not a sealed vessel, some brewers pump the wort into a purged fermentor for acidification. This necessitates returning the acidified wort to the kettle for boiling but also ensures a more effective, controlled purge, while also freeing up the kettle for more brewing.

Cincinnati’s Urban Artifact enjoys a strong reputation for its tart and juicy fruit beers. Their way is to transfer to tanks for acidification, which cofounder and COO Bret Kollmann Baker says is worth the extra work—all part of a detail-oriented approach to creating an ideal environment for their bacterial culture.

“You could brew beer with bread yeast,” Baker says. “But most brewers pick a yeast [strain] with character and take care to give it what it wants. Why wouldn’t you treat your Lactobacillus with the same respect?”

Also, since acidification can be unpredictable, using a fermentor allows Baker and his team to leave the wort for as long as it needs to acidify—rather than for as long as he can afford to occupy a kettle.


Baker also recommends adding manganese for the acidification phase, to encourage the growth of Lactobacillus. Indeed, manganese is what laboratories use to grow lactic bacteria. In Baker’s view, the amount of manganese found in grain is insufficient for Lactobacillus growth. Also, since manganese isn’t needed by Saccharomyces, it is not included in commercial yeast nutrient blends.

Once the wort has been acidified and boiled, it’s ready for yeast. Baker recommends propping up the yeast starter in acidified wort to allow it to acclimatize. At Urban Artifact, they also use 50 percent more yeast nutrient than recommended, and they split it into three additions: pre-acidification, at boiling, and when they add fruit. The latter is typically two to three days after they pitch the yeast.

At Sapwood Cellars, Tonsmeire and team take a similar approach to preparing the yeast and generous nutrients. “If you have a really low pH—3 or so—you can acclimatize the yeast by acidifying the starter,” he says. “Yeast is acid-tolerant, but only to a certain point. So, a little extra zinc and other nutrients combined with a higher pitch rate will help the fermentation.”

Know Your Acidity.

Measured on a logarithmic scale, the pH of wort or beer can easily be read with a meter. However, that number doesn’t tell drinkers a whole lot, and it doesn’t necessarily determine how sour a beer will be perceived on the palate.

In fact, pH doesn’t directly measure the amount of acid in a solution—it’s a measure of hydrogen ion activity since acids release hydrogen ions and bases soak them up. This is why brewers sometimes choose to measure titratable acidity (TA), which instead measures the ability of an acid to neutralize an alkaline substance. This is measured on a linear scale—so a beer with twice the TA should, more or less, taste twice as sour.


At Blue Owl in Austin, brewer and co-owner Jeff Young takes the measurement of acidity a step further—they have their own scale that they call sour units, or SUs. It’s simply the percentage of titratable acidity multiplied by 100, to become a number that drinkers can understand.

“Because we are designing unique beers, we needed a metric to use in formulating recipes,” Young says. “Souring units are based on titratable acidity, assuming it is all lactic acid.”

Because he’s accustomed to brewing with his own slurries, he can push and pull levers—time and temperature—to control the amount and the character of the sourness in his beer, even aiming for a certain number of SUs.

Malt, Hops, and Fruit

“We used to try different malts and hops,” says Baker at Urban Artifact. “But the bitterness of the hops gets in the way of acidity. We found the hops that work best have fruity flavors—and if we want fruity flavors, it’s easier to use fruit.”

Also, in a tart fruit beer, the differences in malt tend to be obscured, so they keep the base straightforward at Urban Artifact—usually just two-row, with a dash of acidulated malt. Instead, what sets the beers apart is careful brewing techniques that assist the microbes. Among other things, that includes first-wort hops to get about 15 IBUs, ensuring a controlled acidity from the Lactobacillus culture; it includes pre-acidifying to 4.5 pH before pitching the bacteria; it includes souring in a purged tank kept between 75–85°F (24–29°C); it includes plenty of yeast nutrients, as discussed above; and it includes attention to sourcing quality fruit purees.


Fruit is an important consideration, given that fruit beer as a popular category has essentially taken the kettle-sour technique and fully subsumed it.

At Sapwood Cellars, Tonsmeire suggests using pre-pasteurized juice or puree when fermenting beer on equipment not dedicated for mixed-fermentation. He also says to keep in mind that fruit will dilute the base beer’s strength if it’s not allowed to referment. Yet if you allow the yeast to consume the fruit sugars, the alcohol produced will roughly offset that dilution in most moderate-strength beers.

The beer also will dilute the fruit’s acidity, with the flavor impact depending on the relative acidity of the beer and fruit—another thing to keep in mind. For example, a highly acidic fruit (such as passion fruit) can provide enough acidity to make a sour beer without a soured base beer.

Tonsmeire also recommends sampling the same fruit from multiple suppliers. “I like certain fruits from one supplier, but for other fruits, I find other suppliers are better.”

Quick acidification using Lactobacillus has become a widespread technique at breweries thanks to its simplicity and efficiency, as well as its ability to reinforce popular fruit flavors. However, the appeal of these beers depends on balance, drinkability, depth of flavors, and attention to detail.


Mastering and dialing in your own approach is what can take them to the next level.

The Blue Owl modular innoculation unit, or MIU. Photo: Courtesy Jeff Young

A Distinctive Souring Approach, Using Grains

Broadly, best practice in the industry these days is to avoid using unpredictable sour mashes and not to pitch grains into wort to get their souring bacteria—two tricks that were once popular among homebrewers.

However, at least one brewery embraces those natural microbiomes that exist on barley malt and uses them for acidification—even if it uses a unique process that’s been carefully honed to avoid off-flavors and preserve drinkability.

“We built our brewery around the idea of integrating acidity into beers people are already familiar with,” says Jeff Young, co-owner and brewer at Austin’s Blue Owl Brewing. (“Like the salsa on your taco,” the brewery says in its Untappd listing, “sourness in a beer should accentuate what’s already there instead of dominating your taste buds.”)

How Blue Owl gets that sourness diverges from the modern approach. Young says he believes there is magic in microbes; notably, he was an analytical chemist for a pharmaceutical company before he became a brewer. At Blue Owl, he eschews pure commercial strains of Lactobacillus in favor of creating and re-pitching his own blends of souring organisms propagated from different grains.


He has built his own “modular inoculation unit,” or MIU—he pronounces it “mew.” Rather than sour in the kettle, Young runs wort through a relatively small amount of fresh, crushed grain in the MIU, picking up their natural microbes. The result is a more controlled type of sour mash.

After going through this souring process more than 600 times, Young says Blue Owl has never had to dump a batch due to off-flavors. However, they do take several precautions, including:

  • pre-acidification of the wort to 4.4–4.6 pH
  • pasteurizing the wort before cooling it to souring temps
  • keeping the range of temperature for souring between 113–125°F (45–52°C) depending on the recipe
  • scrubbing with CO2 while cooling

“There’s no concrete evidence we’ve seen that shows the anaerobic condition is entirely necessary for avoiding aerobic bacteria species,” Young says. “But yes, we do it because it’s easy, cheap, and helps us sleep.”

Also, because Blue Owl has captured a blend of naturally occurring microbes that live in harmony with each other, Young keeps a slurry of it that he can prop up and re-use, just as a brewer would with yeast. He has used this mixed culture for hundreds of generations without trouble, and he says it gives Blue Owl beers more complexity.

Blue Owl also uses the MIU to create terroir-driven beers. They have an occasional series called “SMash SMaSH”—variations on a sour-mashed, single-malt, single-hop IPA. A recent version featured malt from New Zealand and Motueka hops. For this kind of beer, they’ll get their sour slurry by putting some of the base malt in the MIU.

Young believes that he gets a more complex and distinctive beer by harnessing the microbiome on grain, and there is science to back him up. Recently he partnered with researchers at Indiana University to identify the microbes on different sources of barley through DNA analysis. Besides strains of Lactobacillus, they also found a different type of bacteria called Weissella cibaria. The microbes they found produced not only lactic acid, but also acetic acid, succinic acid, malic acid, and pyruvic acid. The point is that different grains can produce unique results.

Blue Owl applies its unusual sour-mash process to a range of styles, including pale ales, red ales, and lagers. While Young says the process ensures a level of repeatability, they have had to adapt virtually every other brewing step.

“We are fundamentally making a different beer,” Young says. With the lower pH, “everything will act differently throughout the process. Hop utilization, yeast, even clarifying agents behave differently. Oil solubility is decreased, so you have to hop more aggressively and find a mechanical way to get those oils into solution. Any yeast will produce different flavors with pH two points lower. Yeast produce CO2 and ethanol, but what about all the other esters and compounds? The materials provided by your yeast supplier describe the yeast under conditions that just don’t apply to sour beers, so we have had to re-characterize all of the yeasts we use. Even fining agents and enzymes, we’ve had to reassess how they act.

“But it’s cool to be doing something no one else is doing.”

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Don Tse is an internationally recognized beer writer and beer judge, working from his home base in the middle of North America’s barley belt.