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Knowledge Base

Perceived Sourness, pH, and Titratable Acidity in Sour Beers

8/13/2019

3 Comments

 
By: TJ Grisel, Beyers Analytical Brewing Sciences, LLC
he rise of sour beers in the craft beer industry has necessitated a standard method to analytically measure the sourness of a given beer. Brewers use pH as a measure of acidity in beers however pH does not reflect the perceived sourness of a beer. Lack of an accurate measure for sour taste can hinder brewers’ ability to establish quality standards for both sour and non-sour beers.
 
If not pH then what can you do to test this sourness? Developments in the production of sour beers indicate that titratable acidity (TA) is one of the best methods to measure the sour taste. TA is defined as the sum of titratable acids by neutralizing the acids with a base. Think back to chemistry class in high school when you would drop something like sodium hydroxide into a solution to get a color change. This is the process that one takes to get these TA values.
 
A study was done to test the perceived sourness and TA values. Beyers Analytical Brewing Sciences, Fermentation Science and Technology program at Colorado State University and Gilded Goat Brewing Company in Fort Collins, CO completed the study. A sensory evaluation was conducted to test the sourness by using a pH meter, TA methods via the American Society of Brewing Chemists (ASBC) and a RedCheck Titratable Acidity kit. The study concluded that a higher TA values were more indicative of higher levels or perceived sourness by the sensory panel. An interesting note is that when they looked at the time it took to take the measurements it was noticed that the RedCheck kit took considerably less time than the other methods of testing TA.
 
The understanding of TA and thus organic acid content is best utilized by the brewer because it bridges the gap between analytical data and sensory perception. This provides an additional control point for the monitoring of out of specification beer.
 
While TA is not a new concept, as it is used within the winemaking industry, it certainly is newer within the beer industry. Those brewing sour beers more frequently are now adding a TA value on the bottles similar to an IBU value. One example where you would see an organization implementing this is, Firestone Walker. The beer Lil Opal was one of the first to display it. As a maker of some great lambics, it seems they see it as a value added to help people understand the different levels of these type of beers. Learning what TA is and understanding this parameter can add consistency when dealing with acids, lactic acid. You must continue to measure pH as it is one of the most basic measurements you can take, and implementing TA through either colorimetric or potentiometric methods will help you dial in the perceived taste of your product.

Whether it is for your own or friend’s consumption or you are starting a commercial brewery, people want to know they can expect a certain flavor from your beers. Don’t fail in this expectation and get the tools you wish use to start measuring titratable acidity.
 
Have additional questions about how the in-house titratable acidity kit works, please contact us!
3 Comments
Adam Bittner link
4/3/2020 01:39:41 am

Hi,
Any theories behind WHY titratable acidity is better correlated with sour taste than pH?

Also, did you publish the experiment?

Reply
Evan
4/3/2020 02:29:33 am

Hey Adam,

My theory is that it has better sensitivity than pH at the relevant concentration ranges. Let me explain:

pH is defined as -log[hydronium ion concentration]. This means that you need a ten-fold change in concentration to move on pH unit (e.g. from pH 3 to pH 4). However, it also means that it is hard to discriminate minor changes in acid concentration. For example, pH 3.6 and pH 3.7 are not very different on the pH scale, but they represent approximately a 20-25% difference of hydronium ion concentration. This poor sensitivity of pH measurements can make correlation hard to obtain because small fluctuations in pH can befuddle measurements. Theoretically, if you had a perfect pH meter and perfect pH measurements, the correlation would exist. Most labs and brewers do not have perfect equipment. Conversely, titratable acidity (TA) measurements generally do not have a wide-range of applicability like pH but they have increased sensitivity.

For example, TA measurements could discern the difference in acid concentration between two samples if one measured 35 mM TA and the other measured 50 mM TA, while both samples would likely have the same pH measurement using standard lab/brewery equipment. This means that you would assume the acidity was the same in the two samples if you only measured pH, but measuring TA would allow you to see the small difference in organic acid concentration (and therefore taste) that exists between the samples.

Lastly, it is important to note that different organic acids have different flavor profiles. pH and TA flavor correlations break-down between different organic acids. For example, 50 mM lactic acid tastes different from 50 mM acetic acid which tastes different from 50 mM gluconic acid, etc. However, TA and pH are great for enhancing reproducibility in brewing assuming the brewer is attempting to standardize the process.

We are working on publishing this data along with HPLC data that we have acquired since the poster was put together by the CSU students. The goal is to show the relationship between pH, TA, and HPLC data in a single manuscript. We have a manuscript in-progress, and we are hoping to submit shortly.

Thanks for the good question. Let us know if you need anything else.

Evan

Reply
Adam Bittner
4/3/2020 07:26:06 am

That's an interesting idea. Thanks for the quick reply!




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