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Understanding pH and Titratable Acidity in Sour Beer: Tools for Brewers and Enthusiasts Alike

Brewers have often used pH to describe the sourness of their beer, but recent research has shown not only that titratable acidity correlates more closely to perceived sourness, but that additional factors are also important. Stan Hieronymus elaborates.

Stan Hieronymus Jun 26, 2017 - 11 min read

Understanding pH and Titratable Acidity in Sour Beer: Tools for Brewers and Enthusiasts Alike Primary Image

Consider the words used to describe the character acidity may add to a particular wine. One with pronounced acidity is described as bright. One with acidity but little substance is thin, and one with very high acidity and little fruit flavor is austere. A soft wine has low acidity, a flabby one even less.

Sometimes the same descriptors are appropriate to use with beer, particularly those flavored with fruit and ones categorized as sour or wild. They are only a starting point, just as are the measurements brewers take to indicate the level of acidity in a particular beer. Here’s how Ehren Schmidt, the “Sour Scientist” at Toolbox Brewing in north San Diego County, characterizes two of them: potential of hydrogen (pH) and tritratable acidity (TA): “pH is the first look, peeking in the window. TA is really putting it under a microscope.”

pH (a measure of the power of an acid in solution) measurements, of course, are used in scores of industries and throughout the brewing process, for both sour and “clean” beers. In a sentence, it is expressed on a logarithmic scale (so that a change of one pH unit corresponds to a tenfold change in concentration) with numbers below 7 more acidic than pure water, those above more alkaline. pH measures only disassociated hydrogen, but the organic acids in fermentation are weak acids and do not disassociate as easily as strong acids. TA (a measurement of volume of acid in solution) measures both associated and disassociated hydrogen. It is not the same as total acidity (although both are referred to as TA), which is harder to measure, but it is a good approximation in both beer and wine.

For a primer on titratable acidity see “Quantify Your Funk: A Primer on pH and Titratable Acidity”, but one important variable is the acid that is used in the calculation because TA basically measures the ability of an acid in beer or wine to neutralize an alkaline substance. Units of TA are quoted in grams per liter, and TA is expressed in terms of those different acids. In wine that’s usually tartaric acid and in beer lactic acid, although other acids can be specified. Unlike with pH, which is logarithmic, the relationship between TA and perception tends to be linear so that when TA doubles, drinkers perceive the beer or wine as twice as sour.

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pH and TA are, first of all, tools that Toolbox’s Schmidt uses in the brewhouse, but in the case of TA, it may also give drinkers a better idea of what to expect when they order a Toolbox beer. Again, the numbers are simply the beginning of a conversation because there’s more to these beers than acidity. “People get caught up in the idea that [more] sour is better,” Schmidt says. That is as frustrating for him as it is for other brewers. “I spend endless hours finding microbes that provide additional flavors. There’s a lot more than the sour aspect.”

A Sensory Challenge

It seems a bit like twenty years ago, when many brewers and drinkers rated IPAs based on IBUs, and more equaled better. Intuitively everybody agrees that is not the case, but when there are numbers to compare, they can be hard to resist. What is needed, Kara Taylor of White Labs pointed out during a presentation at the 2015 Craft Brewers Conference, is more research related to “sourness in beer on the sensory side.” Her presentation—appropriately titled “Sour Beers: It’s more than just pH”—illustrated just how complicated sour can be. She provided details about an experiment in which eleven trained panelists at White Labs tasted eight beers and rated the level of sourness from zero to three (see chart below). Many times individuals ranked some of the beers off the charts (over three).

White-Labs-Sour-Beers

The results illustrate that while pH and TA are most often correlated (i.e., TA will be higher when pH is lower), that is not always the case. In addition, different organic acids have different flavors. They also have different thresholds of perception. Of the four acids Taylor measured, lactic acid has the lowest, followed by malic, acetic, and citric. Of course several other acids—tartaric, succinic, butyric, ascorbic, etc.—may add to the flavor matrix. Other factors that change perception include carbonation levels, alcohol levels, flavors from fruit or barrels the beers aged in, and how hard it was to distinguish between super sour and super, super sour beers.

Consider Beer D, for instance. It had the lowest pH (3.35) but was not perceived as the most sour. Instead the TA was a better predictor, although the higher finishing gravity and lack of acetic acid should also be considered. In contrast, the beer rated the most sour (Beer A) did not have the highest TA but had the second lowest pH, contained acetic acid, and had a relatively low finishing gravity.

More recently, Urban Chestnut Brewing Company in St. Louis gathered information from a broader audience: 355 of its customers. UCBC invites consumers to sample beers (for a nominal price) at its Urban Research Brewery across the street from its production brewery and offer detailed feedback (photo at top). In February, the lineup featured three Berliner weisse beers with varying levels of acidity. One had a pH of 3.8 and TA of 6.1; another 3.5 and 7.2; and a third 3.2 and 12.1.

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The results provide plenty of fodder for future studies—for instance, the third beer rated much higher for umami/savory, and it was easily the most divisive of the three (drinkers liked it first or third). But what was also apparent is that even though a majority of drinkers still rated drinking the most acidic beer pleasurable, as the level of sourness increased, they were less likely to buy it on tap.

Drinkers “Are Ready”

By the time Toolbox’s Schmidt starts blending, he has checked the numbers many times. He regularly takes readings on gravity and pH for all the barrels. He may simply be looking for a drop in pH to signal that what he has added to a barrel, for instance Pediococcus, is doing its job. There are other variables that he can’t carefully put calculated numbers to—like the size of the barrels or how long they’ve been aging.

Fruit is an important ingredient in many of his beers. Fruits obviously have different flavors and varying levels of sweetness and acidity, and those acids may be converted into still other acids during fermentation. Consider citric acid, which obviously is found in citrus fruits as well as berries and tropical fruits. It is a relatively weak acid that is easily converted into lactic acid—which is relatively mild—or by lactic acid bacteria into acetic acid—which is much stronger and often one drinkers requesting “more sour” look for.

Toolbox-Ehren-Schmidt

PHOTO: COURTESY TOOLBOX BREWING

Schmidt measures the TA of each of the individual components, but he decides how he will get to the final blend based on what he tastes, his experience, and what he knows beyond relatively simple numbers. “Finding the balance, finding the barrels, it’s part of the game,” he says. “It’s a definite challenge to find the ones that taste good. To find the ones that have a characteristic the others don’t, that isn’t desirable alone, but when you put them together…”

The process is not completed until bottling day, when he will measure TA again and put the number to the label. He understands TA may change if a customer decides to age that bottle for several months. A beer that contains 12 g/L when it is packaged could be 14 g/L by then. “But that’s the world we live in,” he says. He initially used TA simply as an aid when blending, but Jeffers Richardson at Firestone Walker convinced him to add the number to his labels. Firestone Walker was the first brewery in the country to publicize its TA and Toolbox the second.

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“People are ready for this. They want to know what they can expect,” he says. “This is what a 14 is versus a 10. In the future, other breweries are going to be talking about this.” He doesn’t want the conversation to be only about acidity, but he does want customers to understand it. In the Toolbox tasting room, customers may learn that freshly squeezed orange juice has a TA of between 8 and 10 g/L. They also may try blends of Toolbox beers that are much more sour than those it packages. “Something for everyone,” Schmidt says.

The next conversation isn’t about what comes after acidity but what works alongside it. Schmidt is constantly searching for “stuff I can make beer with” pretty much anywhere he can find it around San Diego. “Too many people can call [a lab] and get the same blend,” he says. He sometimes leaves wort outside the brewery at night to see what lands in it. He keeps a jar in his car because he never knows when he may come across a potential flavor source. That could be bacteria or yeast, although he has a sense that wild yeast adds a level of complexity.

Acidity is a complicated topic; beer is an even more complex one.

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PHOTO AT TOP: COURTESY URBAN CHESTNUT BREWING CO.

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