Loving Lacto

Lactobacillus: the friend who could wreck your party, but you invite them over anyway because they keep things interesting. These bacteria brighten things up with their lively acidity, but if you’re not careful they can get out of hand or overstay their welcome. Love or hate them, acidic beers wouldn’t be the same without Lacto.

There’s more than one way to get lactic acidity in your beer, and each method has different requirements and produces different results.

Kettle souring is an efficient path toward acidity that, when done properly, produces a bright, clean acidity like a glass of lemonade. It’s a one-hit wonder, but sometimes a one-hit wonder is all you need.

Traditional mixed-fermentation souring is the path toward a wider array of acidic qualities. It uses Lacto co-pitched with a cocktail of other yeast and other lactic and acetic acid-producing bacteria. These combinations can create deep, layered acidic characters in the finished beer, but that development only comes with time, often months and sometimes years. That extended timeframe also creates a much larger window for bacteria and other yeast to end up somewhere they shouldn’t (but that’s a longer story for another time…)

Acidity right in the brewhouse

Kettle souring is a crucial tool for brewers who are looking to create acidity in their beers on a tight timeline. It’s also appealing because the whole process is done right there in the brewhouse. There’s no need for separate equipment, and the possibility of cross-contamination is reduced by keeping bacteria on the hot side.

Brewers boil unhopped wort (Lacto is notoriously hop-intolerant) and pre-acidify the wort to a pH of 4.5 or lower with food-grade lactic or phosphoric acid before chilling it. Pre-acidification prior to pitching Lacto is a safeguard against the development of pathogenic bacteria and off-flavors.

Many strains perform well at 90 – 95°F (32 – 35°C), but like yeast, different Lacto strains perform better at different temperatures. Make sure to choose the right temp for the strain, or the batch might not sour. After chilling the wort, just add the Lacto. For a healthy pitch of Omega Yeast’s Lacto blend, the standard pitch rate is 1L of Lacto for every 3 bbl of wort. Some brewers opt to close off the kettle and blanket the wort with CO₂, but that might not make that much of a difference with a healthy pitch.

Time is a factor with kettle souring. The wort will typically reach its target pH/TA within 24 hours, but it will continue to sour if left unchecked. Regardless of those measurements, it’s crucial to taste the flavor progression. Drinkers experience beers with their palates, not lab equipment. After reaching the desired level of acidity, the wort is brought back to a boil, or pasteurization, to kill the Lacto. From there, the process and quality concerns are the same as any clean beer fermentation.

Is there a more efficient way?

Kettle souring can keep Lacto on its best behavior on the quick path toward acidity, but the convenience does come at a cost. At a minimum, the kettle is tied up for an additional day while wort is souring. This could cause problems for brewers looking to streamline their production schedules. There’s also the time and energy costs associated with boiling the wort again to kill the Lacto. So what’s another way?

Even for brewers with solid systems in place to make sure Lacto stays where they want it, there’s always a risk of cross-contamination when bringing any bacteria into the brewery. But what if that doesn’t cause you to flinch and you just didn’t want to mess with it? Could you skip the hassle of added time and steps of co-pitching Lacto and still produce quality acid-forward styles? How could the process be faster and more convenient?

These are the questions that led to the search for and development of yeast strains that produce their own lactic acid. They provide an opportunity to maximize efficiency in the brewery when producing acidic beers.

Found Strains

Some researchers discovered the answer in nature where they captured and isolated non-Saccharomyces strains like Lachancea thermotolerans, which evolved away from brewers yeasts over 150 million years ago. These wild strains were grown up, isolated, and selected for their suitability for beer fermentation as well as their lactic acid production.

The key to Lachancea thermotolerans’ naturally occurring lactic acid production is the presence of the enzyme lactate dehydrogenase (LDH). In this species, the path to lactic acid and ethanol starts off the same. The yeast converts simple sugars (glucose and fructose) into pyruvate through a reaction called glycolysis. Then the LDH enzyme converts a portion of the pyruvate into lactic acid. The rest of the pyruvate is converted into ethanol via the enzyme alcohol dehydrogenase (ADH), just like what happens with yeast that doesn’t contain the LDH enzyme.

Developed Strains

Other researchers embraced technology in search of answers, using gene-editing technology to enhance existing yeast strains with the LDH enzyme. Knowing that LDH can enable other organisms to produce lactic acid in fermentation, researchers were inspired to add LDH to traditional brewing strains. These new innovative strains allow brewers to streamline sour beer production without the added hassle of using alternate yeast or bacteria. ​“Tartango” is a brand new lactic acid-producing yeast strain, developed by Omega Yeast.

Using CRISPR technology, Omega Yeast spliced in the LDH-producing gene isolated from Lactiplantibacillus plantarum, a component in Omega Yeast’s Lacto blend, which allowed Tartango to produce ethanol and lactic acid from simple sugars. Its other characteristics remain similar to those of the parent Voss Kveik strain, including a super clean fermentation across a wide temperature range (68 – 95°F / 20 – 35°C) without phenolic off-flavors, though attenuation may be lower with higher levels of acidity.

In addition to the lactic acidity that complements the parent yeast’s pithy citrus flavors and aromas, the modified yeast provided other benefits. Kveik’s short lag phase helps ward off spoilers. The yeast also could be harvested and repitched without creating additional pinch points for infection in the brewery. Omega Yeast suggests harvesting the yeast and repitching it promptly after primary fermentation to minimize the stress the acid puts on the yeast.

Through early R&D trials, another clear observation was that the beer’s level of acidity had a correlation to its original gravity. The higher the gravity, the more acid produced: for example, a 12°P wort ended up with ~10 g/L in titratable acidity from lactic acid. Expect approximately 1 g/L +/- for every 1°P change in OG, but this may vary depending on the wort’s overall fermentability.

The paths toward creating lactic acidity in the kettle or in the cellar during fermentation each have their strengths and weaknesses.

Traditional kettle souring allows brewers to precisely lock in their desired level of acidity by bringing their wort back to a boil and killing off the bacteria. It leaves their wort just so while eliminating that bacterial threat downstream. However, boiling too hard or long could create a ​“cooked” flavor in the wort or alter the color through Maillard reactions. And, as we know, it ties up your brewhouse for at least another day.

“Cellar Souring” with lactic acid-producing yeasts eliminates the need for an extended stay in the brewhouse, so brewers have more time to get creative with acidic beers and they remove a threat for bacterial contamination. Inoculating wort with these yeast strains from the outset may also eliminate the need to pre-acidify the wort with lactic or phosphoric acid after boiling to ward off spoilers.

The trade-off with creating acidity during fermentation is that brewers really let yeast take the wheel. Brewers can make adjustments to nutrients, sugar sources, and original gravity to try and influence the beer’s final acidity, but ultimately it’s up to the yeast. Some lactic acid-producing strains can go too sour, too quickly, which can make ethanol production sluggish or create a case where blending with another beer is necessary to achieve balanced flavor in the finished beer. Other wild Lachancea strains may also produce unwanted phenolic compounds.

Lactic acid-producing yeasts may also be more viable candidates for repitching compared with regular yeast that’s been stressed by the acidity produced by kettle-soured wort. Brewers looking to repitch lactic acid-producing yeast should harvest and reuse it promptly to minimize stress from the acidity. Viability for repitching is also strain-dependent, so check with your yeast supplier before diving in.

Comparing traditional kettle souring to cellar souring with lactic acid-producing yeasts could be seen as a contest between the quick and the quicker in the pursuit of bright and clean acid-forward beers. Lactic acid-producing yeast may give brewers more time in their production schedules to get creative if they really get to know their yeast, but both routes can produce thirst-quenching refreshers perfect for pool and patio weather. What would you create with these single-strain solutions? Or would you rather keep the Lacto in the kettle? Let us know!