Temperature vs P.H.

[brakspears]

anyone out there know of a temperature / ph correction table, or if such a thing exists, cheers Nigel.

[Mesa Maltworks]

The temperature corrections are usually printed on calibration buffer bottles that that are used to calibrate a pH meter before each session. A "general" table is not made because it would assume perfect calibration and persons using it would chart faulty results. Rather, the temperature corrections listed on the bottle are to ensure that your meter is calibrating correctly when using the buffers. As the meter is calibrating, it should count up or down to within range of the value on the bottle for the given temperature. Once it reaches a steady buffer value, it slopes up or down to the ranged value (usually 4, 7 or 10).

An example is: You are calibrating to one buffer, pH 7. At 25C, the 7 buffer reads at 6.85 pH. If your meter was perfectly calibrated to this temperature, the buffer would read exactly that value. All electrodes are subject to drift and must be calibrated before each use. This is why there is no "general" temperature/pH correction chart. If one was produced, it would assume that all meters are perfectly calibrated and the electrode never drifts. The difference between the actual read of the electrode in the calibration buffer and the reference value (in this case pH 7) is known as the slope. Once calibration is done, the slope value is stored in the meter and corrects all readings as long as the samples are at the same temperature. The only way around this is to purchase an ATC (automatic temperature correction) capable pH meter. These meters measure the temperature while calibrating and measuring and perform complete self correction within their electrode temperature limits.

Eric

[brakspears]

Thanks for your words of wisdom Eric, so can I take it that a sample of wort should be cooled to the calibrated temperature of the ph meter, before a ph reading is taken, can't get a true reading at mash temp (65c), am I correct? Thanks again Nigel.

[Mesa Maltworks]

Yes... unless you have an ATC meter, you have to cool the sample to it's standard calibrated temperature. Most are either 20 or 25C. This is the same for hydrometer samples... most are calibrated between 60 and 70 deg. F. Some hydrometers, however, have a built in thermometer with a factor scale for corrections.

Eric

[brakspears]

Thanks Eric thats been really helpful, good brews to you, Nigel.