By Laura Burns and Shana Solarte
Nov 29, 2022
Introduction
As a part of a sour beer workshop at the National Master Brewers Conference in Cleveland, I had the opportunity to work with Lindsay Barr of DraughtLab to discuss the methods available to brewers for measuring sourness. It was a fun challenge to find ways to demonstrate the concept that pH might not be the most effective method for measuring the perceived sourness — due to various acid strengths and the buffering capacity of different worts, titratable acidity (TA) is the true test.
Measuring sourness
pH is a measurement scale used to determine the acidity or basicity of a solution — for our purposes, of course, the solution is beer. However, pH is a bit limited in that it only measures a small snapshot of the acidity in a given beer by way of the dissociated hydrogen ions.
Measuring titratable acidity is an incredibly useful and practical way to really discover the true sourness of your beer. TA measures free hydrogen ions and hydrogen atoms bound to organic acids, meaning that the reading directly correlates to the amount of acid that has been produced during fermentation.
Before comparing the two, consider acetic acid and lactic acid, the two main acids we tend to encounter in beer. Acetic acid is a major component of vinegar, and therefore adds a vinegar-like character to any beer where it plays a role, like a Flanders red ale. Be careful, though — acetic acid can be perceived as being very sharp when found in high concentrations. Lactic acid is often found in tart foods like yogurt and pickles, and lends a “softer” sourness to beers like Berliner Weisse. From a hedonic standpoint, both acids have their place in some beers and can be quite pleasant to drink.
Acetic acid and lactic acid differ in their strength (in scientific terms, pKa). Acetic acid is weaker (pKa = 4.76), relative to lactic acid (pKa = 3.86), and as a result will require more grams per liter in a given solution to achieve the same pH as the same solution treated with lactic acid.
The test
To better understand the differences between acid strengths at various concentrations, we dosed beer samples with lactic acid and acetic acid to see how the pH and TA measurements would differ. It’s important to note that the beer style used can affect the pH measurement even when the TA remains consistent across all samples. For example, when we added just 2g/L lactic acid to both a lager and an IPA, the pH of the lager came in at 3.2 (sample B below), whereas when we added that same amount to an IPA for comparison, the pH measured 3.82 (not included in the flight below).
Varying concentrations and different beer styles
| Sample | Acid + beer style | pH | TA |
|---|---|---|---|
| A | Acetic + lager | 3.20 | 8g/L |
| B | Lactic + lager | 3.20 | 2g/L |
| C | Lactic + lager | 2.71 | 8g/L |
| D | Lactic + IPA | 3.15 | 8g/L |
Samples A&B — different acids, same pH
Our sensory panel was blown away by the intense sourness of sample A, while finding sample B to have a more pleasant, slightly sour flavor. This comparison underscores the importance of using TA to measure acid content. Stronger acids (in this case, lactic acid) will cause the pH value to drop more dramatically at a lower volume of acid than in comparison with a weaker one, like acetic.
Samples A&C — different acids, same TA
Here we tested a strong concentration of both acetic and lactic acids in the same base beer. Even though lactic is a stronger acid than acetic, our panel found the acetic sample to be much more intense and unpleasant than the sample dosed with lactic at the same concentration. One takeaway here is that each acid has its own unique flavor impact.
Samples C&D — different beer, same acid at same TA
This pair showed how the base beer can affect the final pH, even with the same concentration of lactic acid. Because the IPA sample had different buffering factors, the pH didn’t drop quite as far as the lager, with its more simplified recipe and buffering capacity.
Samples B&C — different TA & pH, same acid
Based on TA, the numbers here would imply that sample C is four times more sour than sample B. But for our sensory panel, while C was more sour than B, nobody perceived the sample as having a fourfold increase in sourness. So while the numbers imply a drastic increase, our perception of sourness doesn’t necessarily increase in line with concentration.
Panelists rated samples A – D based on the intensity of sourness. n=12
Despite both samples being adjusted to the same pH, our sensory panel found Sample A (acetic acid at 8g/L) to be the most intense in terms of sourness, but half the group found Sample B (lactic acid at 2g/L) to be the least intense.
While 2g/L of lactic acid was perceived as the least intense of the four, when the lactic was increased to 8g/L in both the lager and the IPA, panelists still didn’t find it as intense as 8g/L of acetic acid.
Conclusion
One caveat to all of this is that while pH and TA can be helpful measurements for sourness, they don’t supersede the capabilities of the human organoleptic system. Taste your beers! Sensory data can reinforce quantitative findings. If your sensory team is constantly finding a beer to be pleasant at a given pH, keep making your beer to that specification. Also, remember that while pH will change throughout fermentation, TA will remain the same from wort to finished beer. Measure your TA and discover what to aim for as you continue to dial in your recipes.
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