Measuring Titratable Acidity
This tool uses the calculation from the American Society of Brewing Chemists, Beer Method 8. Measuring Titratable Acidity is an important tool for brewers to use to understand exactly how much of a particular acid (lactic acid most often) is in a beer. Whereas total acidity identifies the total amount of all acids in solution, titratable acidity can be used to identify specific individual acids. As lactic is the most prominent acid in beer, this tool uses the ASBC beer method #8 to help brewers calculate the amount of lactic acid in solution.
What is Total Acidity?
Typically each acid is reported as a concentration in grams per liter (g/L)
What is Titratable Acidity?
Measures how much a strong base (ex. sodium hydroxide (NaOH)), it takes to reach a basic pH (typically pH 8.2).
This details the total available hydrogen ions and is a more accurate to measure of perceived sourness
Is typically reported in either g/L or a percent TA, g/100ml.
In beer, this calculation is used to measure lactic acid (the most prominent acid in beer), for other beverages (cider for example) this calculation can be modified to reflect their prominent acid.
How to Measure:
- pH meter
- degassed beer sample
- stir plate with magnetic stir bar
- sodium hydroxide (NaOH) in liquid form (typically sold in 0.1M form)
- Pipettes and glassware, with precision down to 0.1 mL (25 or 50mL buret)
- Take the specific gravity of the beer.
- Take a precise amount of degassed beer (ex. 50ml) in a beaker.
- Using the liquid NaOH and your pH meter, measure a precise amount of the NaOH (usually around 0.1-0.5ml) into your beer sample, stirring each time you add the NaOH.
- Take a pH reading.
- Continue adding the NaOH in 0.1-0.5ml increments until you reach 8.2pH (at this pH you have reached the point where NaOH and lactic acid are equivalent in the solution).
- Add up the 0.1-0.5ml increments, or the total volume in ml, it took to get to 8.2pH point. This is your ml 0.1M NaOH number.
Calculating mL Lactic Acid and g/L of a Specific Acid
- Now we can do math. You will need:
- volume of beer
- the ml of 0.1M NaOH used to get to 8.2pH
- and the specific gravity of your beer.
- There are two different calculations that will provide you ml of lactic acid per 100g of beer (Equation A below) or, another calculation to provide you with g/l as a specific acid (Equation B, more common).
TA = 5.6ml x 10/50 x 1.010
TA = 56/50.5 = 1.11
Or 1.11ml of 1.0M alkali per 100 g of beer.
Total Acidity (mol/L) = ml x 0.1M / vol of beerEx. Total Acidity (mol/L) = 5.6ml x 0.1M / 50ml = 0.0112 mol/L
Now we need to find the g/L of lactic acid:
g/L Lactic Acid = TA (mol/L) x (90g/mol)*Ex. g/L Lactic Acid = 0.0112 mol/L x (90g/mol) = 1.008g/L
*The 90g/mol is a standard correction for lactic acid
You can also express this number as a % lactic acid by
% Lactic Acid = g/L lactic acid / 1,000gEx. % Lactic Acid = 1.008g/L / 1,000g = 0.0018 x 100 = 0.18%
For more information you can visit https://www.asbcnet.org/Methods/BeerMethods/Pages/Beer-8-SuppInfo.aspx
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