Balancing Lactic Acid in Sour Beers

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Few things are as satisfying as tasting a newly opened homebrew and having it meet your expectations. Even more satisfying is when that beer is from the somewhat unpredictable realm of sour beers. Not all sour beers have to be left up to chance in order to achieve predictable results however, especially when trying to balance lactic acid.
Lactic acid is produced when lactic acid bacteria (LAB) converts carbohydrates into lactic acid. In addition to beer, it is also found in kombucha and dairy products such as buttermilk and yogurt. Two strains of LAB are available for producing lactic acid in beer, Lactobacillus and Pediococcus. An entire article could be devoted to the different characteristics of Lactobacillus and Pediococcus, so for the purposes of this guide I’ll stick to solely to methods for balancing the sourness and lactic acid produced by these bacteria.

Balancing Lactic Acid




Balancing lactic acid, and sourness in general, is mostly about taste perception. Several factors can contribute to a beer tasting sour: a lower pH, a lower specific gravity (will increase the perception of there being more acid, not the actual amount of acid) and the production of more lactic acid. The pH scale runs from 0 (most acidic) to 14 (most alkaline), with 7 being neutral. Sours are generally in the 3.0-3.9 range. Each 1.0 change in pH means a substance is ten times more acidic or alkaline. So a beer that has a pH of 3.1 is ten times more acidic than a beer at 4.1. Additionally, if using brewer’s yeast to finish fermenting a beer know that it can have issues as the pH decreases, especially at 3.4 and below. Always pitch a healthy starter and consider adding beer nutrients to ensure the yeast is strong enough to ferment despite a lower pH. Fruit additions to beer will also lower the pH as they naturally contain malic and citric acid and will produce lactic acid when fermented by LAB. Paper pH strips can be used to monitor levels, but a digital pH meter will produce more accurate results.
Several methods are available for producing lactic acid in beer, and thus the perception of sourness. The easiest method is to simply just add pure lactic acid at bottling. This offers the benefit of essentially flavoring to taste, but can potentially result in a chemical or salty flavor and one-dimensional sourness. For this reason it is best used as a slight boost or compliment to an already soured beer.
For a lighter tartness a brewer can add a percentage of acidulated malt to the total grist of their mash. Acidulated malt (also known as sour malt or sauermalz) is malted barley that contains a percentage of lactic acid by weight. According to malt producer Weyermann, acidulated malt can be used at a rate of 1% of the mash bill to lower the pH by 0.1%. So for a mash with a pH of 3.9 an addition of acidulated malt equal to 2% of the grist will lower the pH to 3.7. To reach a sour character typical in a Berliner Weisse-style beer, Weyermann suggests using Acidulated Malt at a rate of 8% of the total malt bill. Beers that rely solely on acidulated malt for a sour character will not be as complex as those fermented with LAB, but also don’t run the risk of contaminating brewing equipment and offers more control over the sourness of a beer than a pure pitch of bacterial culture.
If using LAB to produce the lactic acid in a sour there are essentially two ways to increase the amount of sourness and production of lactic acid. Depending on what the specific gravity of the beer is, either more sugar can be added to a fermenting beer or an additional volume of LAB to increase the level of lactic acid. In “American Sour Beer: Innovative Techniques for Mixed Fermentations”, author Michael Tonsmeire suggests that for a beer above 1.006 to pitch additional LAB to consume the remaining sugars, and for a beer below 1.006 to add sugars in the form of additional wort or fruit. Additions later in the fermentation cycle will produce higher levels of acidity since at this point the wild yeasts and bacteria have become the dominant organisms. Fruit also contain malic and citric acid, which can be a sharper flavor than lactic acid, however LAB will also convert malic acid into lactic.

Kettle Souring for Lactic Acid



Sour Mashing and Sour Worting (aka kettle souring) are two ways to introduce lactic acid to a beer with the advantage of producing a more complex beer than adding more acidulated malt or pure lactic acid, and with more control than pitching a pure LAB culture. A sour mash is conducted by letting a finished mash cool to a temperature where LAB already present on the grain will produce lactic acid (between 100 and 120 degrees), and holding the temperature so the bacteria can sour the wort prior to boiling. Unless the wort can be kept at a constant temperature and also monitored at regular intervals, there is a higher potential for producing a wort with extreme off-flavors from unwanted bacteria that may also be present in the grain. Emboldened by a successful sour mash on my first try I attempted this method for a second brew, but allowed for a few extra hours to try and achieve a higher level of acidity. Those extra hours helped develop of aromas and flavors that led the batch to being referred to as the “Parmesan feet Berliner Weisse” due to the development of butyric acid. For that reason I now use only kettle sours, but some brewers claim a bready or sourdough flavor can only be achieved through this method. To help a sour mash along, a starter sour mash can be made a few days in advance of brew day at a 1:4 ratio of the total malt bill. Add enough acidulated malt to the starter mash to get the pH down to or below a pH of 4.3 to discourage funkier bacteria from taking hold before the LAB can do its work. Add a LAB culture to the mash once it’s cooled to at most 120 degrees and hold it between 100 and 115 degrees. Continue to sour the wort for anywhere from about one to three days, tasting periodically. Once the desired level of sourness is achieved a “clean” mash can be conducted according to your normal mash schedule and blended with the sour mash upon completion. Because the sour mash only makes up one-quarter of the total mash make sure to account for the amount of acidity as it will obviously decrease when blended with the larger clean mash. Sparge and boil as usual before chilling and adding a clean brewer’s yeast.
For a kettle sour, the wort is collected and the spent grains left behind. Prior to fully chilling the beer to temperatures optimal for brewer’s yeast, LAB (or a handful of crushed grains as they naturally contain LAB, but are also more risky as they could contain beer-spoiling organisms) is introduced to the unfermented wort. For an added step in ensuring unwanted bacteria is not left over from the grains, a quick boil can be conducted (10 minutes is plenty) before pitching LAB. However, boiling is not completely necessary. Bringing the wort to pasteurization temperature of 180F to 185F and holding it there for 10 minutes will kill the present bacteria as well.
Chill the wort to below 120 degrees and like a sour mash, keep the temperature between 100 - 115 degrees. Once the level of sourness is achieved (typically 24 hours or so) the wort is boiled, killing off the LAB so no additional lactic acid can be produced. The wort is then chilled and pitched with brewer’s yeast. Note that the sugary, sweet wort will give the perception of a less-sour beer. If the beer seems to be not quite sour enough err on the side of boiling earlier as the sweetness will ferment out once brewer’s yeast is introduced, resulting in a beer with a higher perception of sourness. Be extremely cautious when boiling wort that has been introduced to lactobacillus though. Depending on whether the LAB is hetero-fermentative (able to produce other products in addition to lactic acid), it can also produce alcohol. Alcohol vapors can ignite (ethanol boils at 172 degrees) if boiled, so be sure you do so in a well-ventilated area. To check whether any alcohol has been produced a specific gravity reading should be taken prior to the introduction of LAB to see if it has dropped once you have decided to kill off the bacteria through boiling.
To discourage the production of lactic acid hops are the perfect agent for staving off potential bacterial infections. Even a small amount of hops could derail an otherwise intentionally sour beer as well as keep an already sour beer from producing additional lactic acid. An IBU as low as 5 could be enough to keep the LAB from replicating or even surviving. Additionally sour and bitter don't typically work well together, so keeping the IBUs well below 10 is not unheard of.

Blending Sour Beers



To achieve balance while exhibiting both control and also allowing for the LAB to fully do its work, blending is the best option. A recent batch of Old Ale I brewed was made infinitely better through blending. After fermenting with an English ale yeast the gravity had not dropped to the level I was hoping for, leaving for a slightly cloying beer. Luckily, I had taken a quarter of the batch and added the dregs from a Spanish cider as well as dregs from a Jolly Pumpkin Artisan Ales beer. That soured beer ended up becoming too much so for my liking, so I made a blend of the two to balance each other out. To achieve the right blend I simply poured equal amounts of each split batch and blended into glasses while noting the ratios. Once the desired ratios were recorded, I pasteurized the sour batch prior to blending with the English ale yeast batch, otherwise the LAB and other bugs would have consumed the unfermented sugars from the non-sour beer, creating both excessive carbonation, more alcohol and additional lactic acid. Again, caution must be taken when pasteurizing beer due to the flammable nature of ethanol. If you are going to bulk pasteurize by applying heat to a fermented beer do so at lower temperatures for longer periods of time to be safe. Typical rules of thumb are 150 degrees for 30 minutes, 160 degrees for 20 minutes or briefly at 180 degrees. Once pasteurized chill per your normal brewing procedures and prime if bottle conditioning. If the entire blended batch is pasteurized additional yeast needs to be added prior to conditioning. Other options such as chemical pasteurization (through the use of campden tablets) or filtration can also be used based on your preference.
Ultimately, how you go about souring your beers through lactic acid will result in a variety of different finished products. So experiment with the multiple methods and note both the different results and the process undertaken to figure what works best for your home brewery. For lightly tart styles such as gose the addition of acidulated malt works to both produce a quickly sour-flavored beer and one that is repeatable and easily modified through recipe formulation. For beers like guezes and Flanders Reds and Browns though it’s worth the extra effort and time to let a LAB culture work its magic over a period of time and blend with a sweeter or less-acidic beer to balance out any excessive sourness.
Sources used in research:
Zymurgy - July/August 2013 “Kentucky Common Beer”
American Sour Beer: Innovative Techniques for Mixed Fermentations, Michael Tonsmeire, Brewer’s Publications
Weyermann malting FAQ website
 
Cody Gabbard
Did you know that pH readings are affected by temperature? Having a digital meter with a temperature sensor not only "kills two birds with one stone" but also helps with accuracy.
 
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