The perception of sourness or tartness isn’t easy to explain.

Tartness is a sensation on the tongue caused by hydrogen ions (H+) of an organic acid on the tongue’s flavor receptors. In sour beer, it is the presence of these organic acids–produced by wild yeast, fruit additions, as well as lactic acid bacteria fermentations–that define this style of beer. Of the four main organic acids that play a flavor role in sour beer, Acetic, Lactic, Citric, and Malic, the two acids that are in the most direct relation are Lactic and Acetic.

Often, we are asked the difference between measuring these acids using pH and titratable acidity. The short answer is that pH is measuring the concentration of “free” hydrogen ions as donated by acid molecules in solution, whereas titratable acidity–or T.A.–is quantifying the total amount of these hydrogen ions, whether they are “free” or still bound to weaker acid molecules. The pH value is expressed in a logarithmic scale, while T.A. is expressed in a linear fashion, similar to bitterness or color.

In beer making, measuring pH is critical in many steps, like adjusting mash pH acidity for optimal enzyme activity or acidifying brew kettle or whirlpool wort prior to fermentation. Final fermentation pH can also tell you a lot about your yeast health or cellaring techniques. As a visual reference, think of pH as a way of measuring optimal windows for enzymatic or chemical reaction. But for all pH does in beer making, it comes up short with regard to flavor. Since we taste acids and not pH, it’s titratable acidity that better describes the experiential sourness of beer. Further, it’s easy to find two beers with the same pH but different levels of perceived sourness — another example of why pH isn’t the right scale to measure acidity in beer.

In the early years of our Barrelworks wild ale program, we were searching hard to find an assay to promote a consistent level of acidity in the beers in a timeframe of about 16-24 months of barrel time. The floras used were predominately Brettanomyces, used as a base, with a mix of lactic acid producing bacterial organisms, particularly Lactobacillus and Pediococcus. Not for lack of trying, but measuring the pH of these beers left us scratching our heads. Often, we would find one barrel to taste extremely sour, but the barrel right next to it would have a soft, agreeable, and balanced tartness — despite both being from the same batch, aging for the same duration, and using the same souring organisms. Strangely, these barrels would have close to an identical pH.

Curious for answers, we reached out to our winemaking neighbors and learned an interesting trick. Because of this pH enigma, winemakers had adapted to using titratable acidity to get an absolute quantification of acid in their samples, allowing them to define upper and lower limits of T.A. that would relate to the tactile sensations these acids had on qualities like mouthfeel, aftertaste, and overall drinkability. The winemakers jokingly called the test for T.A. “Tactile Acidity” because it had more to do with how wine felt in your mouth and, ultimately, drinkability.

We adopted this technique at Barrelworks during our blending session to help create the perfect, balanced sourness with satisfying and consistent drinkability in our beers. To help our fellow beer lovers begin to understand this important aspect of blending as related to mouthfeel and flavor, every bottle of Firestone Walker Barrelworks wild beer now has a printed Titratable Acidity number on the label.

What is the T.A. Scale?

Titratable acidity is measured in grams per liter, and it basically measures the ability of an acid to neutralize an alkaline or basic liquid. T.A. can be manipulated to measure the most prevalent acid solution — and for beer, that is almost always lactic acid. T.A. and acidity are two elements of flavor. Take a look below at the T.A. of different beverages, many of which aren’t associated with sour intensity:

Apple juice — 3.6 to 8 g/L Malic Acid
Orange juice — 8 to 14 g/L Citric Acid
Cola soda — 18.3 g/L Phosphoric Acid
Energy drink — 51.9 g/L Citric Acid

In comparison, here are the T.A.s of some Firestone Walker Barrelworks beers, which are a blend of Lactic and Acetic, estimated at a 4:1 ratio:

Primal Elements — 6.1 g/L
Frazzle Sass — 10 g/L
Big Mood — 10.1 g/L
Blue Love — 10.2 g/L
Champs de Fraises — 11.6 g/L
Nec Bones — 14.2 g/L

We might be able to categorize T.A.s as:

5 to 8 g/L — light acidity, easy drinking tart beer
8 to 11 g/L — medium acidity, balanced drinking sour beer
11 to 17 g/L — high acidity, noticeably sour as a main flavor component
17+ g/L — very high acidity, the character of the beer is. likely overwhelmed by sour intensity

T.A. in Context

As beer consumers, many of us have come to rely on several different measurements to understand a beer before it’s even tasted. IBU measures bitterness (read our blog on International Bitterness Units here), ABV tells alcohol content, and SRM shows color and opaqueness. Titratable acidity does the same with the experienced sourness in beer.

This being said, the T.A. level and perceived sourness isn’t an absolute. Acidity can be balanced in beer by a number of other characteristics like sweetness, fruit character, bitterness, alcohol, and even carbonation. The balance of any beer is determined by its overall character.

Click here to browse all the Barrelworks beers available for purchase at our online store, or plan a visit to our Buellton location, home of our Barrelworks wild ale cellar.