Titratable Acidity

Titratable Acidity (abbreviated as TA) is an approximation of the Total Acidity of a solution, and has long been used in the production of wine. It is expressed in units of grams per liter (g/L). Titratable Acidity is often mistakenly confused with Total Acidity, but they are not the same thing (see reference). While Total Acidity is a more accurate measurement of the total acid content of a solution, Titratable Acidity is usually used because it is easier to measure . TA has also proved to be a useful way to measure perceivable acidity in sour beer .

TA versus pH

Many sour beer producers use pH to help determine how "sour" their beer is in relation to a set goal, previous batches, or commercial examples. However, often times TA is a more useful measurement of how acidic a beer will be perceived on the palate.

pH

In chemistry, pH is the negative log of the activity of the hydrogen ion (H+) in an aqueous solution. Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline. Pure water has a pH of 7.

The pH scale is traceable to a set of standard solutions whose pH is established by international agreement . Primary pH standard values are determined using a concentration cell with transference, by measuring the potential difference between a hydrogen electrode and a standard electrode such as the silver chloride electrode. Measurement of pH for aqueous solutions can be done with a glass electrode and a pH meter, or using indicators.

pH measurements are important in medicine, biology, chemistry, agriculture, forestry, food science, environmental science, oceanography, civil engineering, chemical engineering, nutrition, water treatment & water purification, and many other applications .

pH is best tested in sour beers using a PH Meter and is most useful for biological parameters. Cells live or die based on pH, not TA. This means pH should be used when testing sanitizer, sour worting, starter cultures, etc.

Why TA?

When attempting to use pH for sensory parameters (how sour something tastes), the measurement falls short. Humans perceive acidity from tasting acids rather than the dissociated H+ ions which determine pH. With strong acids, where the H+ ions are fully dissociated from the remaining acid molecules, the amount of acid is always equal to the amount of H+ ions. However, lactic acid, the primary acid in sour beer, is a weak acid. Weak acids do not completely ionize/dissociate, leaving some portion of the H+ still bound to the acid. The degree to which a weak acid dissociates depends on the identity of the acid and the composition of the solution it is in.

Any acid not dissociated (in other words, an acid still holding onto its H+) does not affect pH. On the other hand, humans will perceive an increased "sourness" based upon the amount of acid in a beer, dissociated or not. The best way to test for total acidity, regardless of dissociation, is using a test called Titratable Acidity. Because different acids have different characteristic flavors and some acids might taste more smooth or aggressive than others (think lactic acid verses acetic acid), samples with the same titratable acidity may have either different perceived acidity or acidity that seems more or less pleasant than other samples. However overall titratable acidity does show a stronger correlation to perceived acidity than measures such as pH.

Kara Taylor at White Labs has done a reasonable amount of professional sensory panels showing the correlation between TA and perceived sour taste, as well as showing a more poor correlation between pH and sour taste. Her full presentation, where most of this information was sourced, is available to any attendee of the 2015 Craft Brewer's Conference.

Testing for Titratable Acidity in Sour Beer

Equipment Requirements:

1. pH Meter with Automatic Temperature Correction
2. Buffer/Testing Solutions for pH Meter
3. Buret (100mL recommended) with Stopcock
4. Buret stand (can be DIY)
5. 250ml - 500ml Beaker (or pint glass, etc)
6. 0.1N Sodium Hydroxide (NaOH)
7. Accurate way to measure 50mL (can use the buret for this, but I recommend a serological pipette or high-grade graduated cylinder)
8. Coffee filter or some other way to decarbonate beer (shake and vent repeatedly, pour through filter, etc)
9. Hydrometer

Procedure

1. Calibrate the pH meter.
2. Pipette 50mL of decarbonated beer into the beaker.
3. Place the pH probe and the ATC thermometer into the beaker, submerge tip of the probe into the beer.
4. Fill the buret with 0.1N of NaOH.
5. Open the Stopcock and add the NaOH to the beer until pH meter reaches a reading of pH 7.0.
6. Upon reaching 7.0 pH, slowly add more NaOH until pH meter reads exactly pH 8.2, keeping track of how much NaOH is added.
7. Record the total amount of NaOH used to reach pH 8.2.
8. Use the following formula to find the Titratable Acidity: Titratable Acidity = (mL 0.1N NaOH * 0.9) / (mL beer * S.G.)
9. The number you get is TA in grams/L.

Uses in Sensory & Further Reading:

• It may be best to compare the ratio of Titratable Acidity to Final Gravity as sweetness counter-acts acidity in sensory experiments .
• More information on this procedure is available from the American Society of Brewing Chemists, who publish a similar set of procedures under the name "Total Acidity with Potentiometer".
• Jim Crook of Firestone Walker has created a presentation about blending sour beers using TA. Contact him for a copy.