BigNastyBrew wrote:Ok, so I just ordered the smaller pHep pH meter from B3 and it says auto calibrated to 140°. So, what do you do when you're mashing at 150°+?
It says "Automatic temperature compensation from 32 - 140 °F" and that makes sense. "Auto calibrated to 140°F" doesn't make sense, at least to me.
It is absolutely essential that a pH meter be calibrated at least once each day you use it. If you don't do this readings are pretty much worthless because we look for small changes in brewing and meter drift can amount to more than some of the pH changes we are interested in. Also, a pH electrode should be stored in a storage solution recommended by the manufacturer.
pH measurements on mash (or wort) should be done at room temperature. This is because all the pH readings you will see in the literature are done at laboratory temperature (pH shifts a couple of tenths of a unit between kettle and room temperature and a little less between mash and room temperature) and, more importantly, because the less thermal stress you put on the delicate glass bulb in the sensor the longer it will last. I'm currently getting over 2 years. The temperature limit of 140 suggests that the instrument might be damaged at higher temperatures. So take a small sample in a small beaker, shot glass or whatever you have and let it cool down. It doesn't matter whether grains are present or not (but they can wedge up in the probe between the guard and bulb and should be removed if they do). Be sure to follow the manufacturers instructions for calibration (e.g. thorough rinsing with distilled water betwen measurements) for calibration, use fresh buffers and protect them from dilution (or other contamination). Store the electode in manufacturers approved storage solution.
Finally, a pH meter is like any other instrument. There is a learning curve. Practice with your meter on stuff around the house. Milk, for example, has a pH of around 6.7, vinegar around 2.4, a baking soda solution (in distilled water) about 8.3, lemon juice 1.8-2.3, distilled water about 5.65 (but this is hard to measure). If you encounter a strange pH number in brewing rinse the probe thorougly with DI water and check against the buffers - fresh in a separate container i.e. not the ones you did the cal with.