pH meters and Automatic Temperature Compensating

hanna ph checkerRecently I have been doing a lot of research for my upcoming water chemistry class with the goal of making a comprehensive, practical class for the home brewer to improve the quality of their beers with water adjustments. Measuring pH is a large part of my research. In a nutshell, pH is the measurement of acidity or basicity of a solution. As home brewers we are mostly interested in measuring pH for proper mashing techniques and flavors. The best way to measure pH is by using a pH meter. A properly maintained and calibrated pH meter will give you fast and accurate readings. The one piece of misinformation I keep running into during my research has been about pH Meters with ATC (automatic temperature compensating). The pH of a solution will be lower (more acidic) at higher temperatures. This is because the energy of the liquid makes it easier to split hydrogen protons from acidic molecules in the mash. At mash temperature (140 to 160˚F) the pH can be .2 to .3 lower than at room temperature (68 to 75˚F).(1) Another reason for lower pH readings at higher temperatures is the meter itself. Warm temperatures change the electrical response of the probe and will create an error in the reading. This is where the ATC function of the meter comes in. It will compensate for its own error when measuring at higher temperatures. It does not compensate for the change in pH from mash temperature to room temperature. Just like hydrometer readings which assume you have adjusted the reading for 59˚F, the brewing pH that is referenced always assumes that you are measuring at room temperature. The confusion that I have seen during my research is the assumption that if you use a pH meter with ATC that it is compensating for the temperature that you are taking the reading at, and then adjusting the reading for room temperature. This is not true. The ATC function is only adjusting for its own error. Take your reading at room temperature as it's the best way to assure a proper reading. It's easy, just take a very small sample and put it in the fridge for a minute or so. Take a temperature reading and then your pH reading. This way you don't have to worry about error compensation from the meter and you will get the proper target pH reading. An ATC pH meter is not necessary for homebrewing. Remember to always calibrate your pH meter with fresh calibration solutions, clean the probe with the proper pH meter cleaner and store the probe in pH meter storage solution. You will have accurate readings and your meter will last much longer. In the future I will discuss more about pH, how and why to adjust it and more about meter maintenance. John John LaPolla Headshot (1)
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