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​​Beer 9. pH (Hydrogen Ion Concentration)​​​​​​​​​​​​​​​​

pH is one of the most important and simple metrics to monitor throughout the brewing process. This method details how to carry out measurements and calibrations using a digital pH meter to ensure accurate results.

Figure 1 - Click to englarge

Digital pH meters consist of two parts; a probe and the meter. The probe is what will be submersed into the sample and the meter is the computer that will display the results. These can either be two separate parts connected by a cord (see Figure 1) or contained all in one.

Figure 2 - Click to englarge

When performing a calibration, the computer within the meter creates a calibration curve where pH is the x-axis variable and voltage is the y-axis variable, or the response (see Figure 2). Depending on the meter, calibration curves can either be a one, two, or three point calibration using 4.0, 7.0, and 10.0 pH buffers. A calibration curve will be more accurate the more points used so if possible calibrate with three points. If limited by the meter, calibrate closest to the range of the samples. For beer this would be a pH of 4. This demonstrates why it is important to use fresh, unexpired buffers. If the buffers are not the values you expect them to be the calibration will be inaccurate and so will the pH results.

Figure 3, image credit: Katie Fromuth - Click to Enlarge

​The glass electrode probe is filled with a potassium chloride (KCl) solution with a neutral pH of 7 and a known amount of hydrogen ions. The storage solution is also a potassium chloride solution to keep the hydrogen ions inside the probe constant. If a test solution is acidic it contains more hydrogen ions than inside the probe. The opposite is true for basic solutions. The hydrogen ions inside and outside the glass electrode will interact and create a difference in voltages between the measuring electrode and reference electrode (see Figure 3). The voltage (mV) response is based off of the Nernst Equation. Using the calibration curve, the meter will compute what pH the test solution is.

Green Chemistry

Green Action	Principle	Benefit
Degas by sonication or agitation	​ Prevent Waste	Eliminates costs and wastes associated with degassing by filter paper.
Compost filter paper if use for degassing is necessary.	Atom Economy	Minimizes filter paper waste to landfill

• ​All pH meters and probes work under the same fundamental principles however, always refer to the manufacturer’s recommendations for how to calibrate, and cleaning and storage (calibration, cleaning, and storage) instructions.
• If you have misplaced the manual they are often found online and are free to access. Simply search the manufacturer and model number.
• As with any instrument, if taken care of properly a pH probe can last a long time. If it is not kept in the correct storage solution and regularly cleaned it will reach the end of its life much quicker.
• Keep a backup probe in house for when the pH probe stops working. This is inevitable.
• There are many different types of cleaning solutions for probes based on the solution being tested. For beer, use a cleaning solution that will remove proteins.
• Typical cleaning regimes require a 15 minute soak in the cleaning solution followed by rinsing with reagent water and then soaking in the storage solution for 2-3 hours before using again.
• Do not leave the pH probe in wort, beer, or distilled/deionized water. Take a reading and return immediately to its storage solution after rinsing with reagent water. Wort and beer will rapidly build up protein on the probe requiring more frequent cleaning. Distilled/deionized water will leach the internal ions out into the water solution due to concentration gradients; an area of high concentration will diffuse to an area of low concentration.
• The storage solution for a pH probe is a 3.5M Potassium chloride (KCl) solution. You can order from laboratory supply stores or prepare in house.
• If storage solution is not available, the pH 4.00 buffer can substitute as a temporary storage solution.
• Never pour calibration buffers back into the storage bottle.
• If additions to a sample are to be made after racking or filtering, the final pH should be taken after the additions to ensure the measurement is taken on a sample that is representative of the bulk volume.

​A ​Big Thanks To...

Ann Sandbrook, Joe Palausky, & Katie Fromuth