Measuring Low Acid Coffee
In this post, I will address the quantitative aspect. Acidity levels in coffee are typically measured with two different methods.
- PH Test
- HPLC Analysis
The first and most popular method is by measuring the PH level of a coffee after it has been brewed. In case you are ever on Jeopardy, The PH scale, which stands for possibility of hydrogen, is the scale used to report how or acidic or basic a substance might be.
The second method of determining acid levels in coffee would be through the use of a High Performance Liquid Chromatography (HPLC). The HPLC is an instrument used to provide an analysis of the chemical composition of a given substance. In the case of coffee, the HPLC analysis can isolate for quantify the amount of Chlorogenic acid in a coffee bean. Both methods on PH testing and HPLC chemical analysis can give a measure of the level of acidity in a given coffee.
The PH method is used to assess the acidity in a aqueous mixture, which is a fancy way of saying in liquid form. A brewed cup of coffee would be an example. The HPLC analysis uses the dry weight of the chemical substance, which might be expressed in milligrams.
By the numbers, a given liquid will return a value on the PH scale between 1 to 14. On the PH scale, 7 is considered to be neutral. Any aqueous mixture less than 7 is considered acidic and any liquid over 7 rated basic. Battery acid would measure 1 on the PH scale being very acidic, and ammonia being a basic mixture would rate around 12.
Most coffees will measure on the range of 4.5 to 5.0 on the PH scale. The non specialty grade coffees you will find in a can at the supermarket are very acidic measuring closer to 4.5. Most specialty coffee today, including the national coffee chains, score closer to 5.0, which still retains a significant level of Chlorogenic acid.
Low acids coffees are closer to 6.0 on the PH scale. The PH scale is a logarithmic scale. Logarithmic means that a change in 1 unit of PH is expressed by a ten-fold increase or decrease in percentage. To make this more clear, let’s look at an example of two different coffees.
PH Scale examples:
Coffee #1: Bucks House: PH 5.0
Coffee #2: Mavericks House: PH 5.8
Using the PH, which is expressed on a logarithmic scale (PH+ -log[H+]), coffee #2, Mavericks House, would be 80% lower in acid then Coffee#1, Bucks House. So what might appear as small differences in the PH at .8 is actually very mathematical relevant. For sensitive coffee drinkers that might be the difference in being able to drink and enjoy a cup of coffee versus not being able to drink a cup of coffee at all.
For the HPLC method, chemical compounds within the coffee bean can be isolated and analyzed. In the case of studying acidity in coffee, we are actually discussing the levels of Chlorogenic acid present in a coffee bean. Chlorogenic acid is an organic acid compound that exists in relative high concentrations in coffee and is arranged at the molecular level in nearly a dozen configurations. If you are ever on Jeopardy, these chemical configurations are called Isomers, which simply means the same.
These isomers are all still classified as Chlorogenic acid, they are just arranged differently. The arraignments impact how each of these isomers are affected by heat during the roast. The HPLC analysis, can not only tell us which organic acids such as Chlorogenic acid are in the coffee, it can also detail which specific Chlorogenic acid configurations (isomers) are present and how they where affected by the heat during the roast.
This can be important for several reasons. Obviously, Chlorogneic acid can affect people with sensitive stomachs. Additionally, Chlorogenic acid can also be associated with bitterness and other unpleasant flavor notes in coffee. This information can also help develop a roast profile to not only minimize acidity but also provide a smoother and better tasting coffee, which incidentally are both hallmarks of slow roasting.