Quote:
Originally Posted by CamelToeJoe
Have you ever used a pH meter?. Getting down to two decimal places is over kill.. and can change in five minutes.. you'll be chasing that number unless you load up on buffers.
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No, it's definitely not. The desired range of mash pH is 5.3 - 5.5. At 0.1 resolution that's 3 bins. How are you going you going to make meaningful fine adjustments within that range? And what does loading up on buffers have to do with it? Anyone using a pH meter must "load up" on buffers and use them every day he uses the meter as a minimum.
As for "chasing" the readings - that's quite important as it takes time for the reactions which establish mash pH to go to completion and it is only at that time that one should read the meter. Watching the drift over time tells you when that time is. Some of the more expensive meters keep track of this for you automatically e.g. beep and freeze the display when the electrode voltage variation settles out. These are typically working with a resolution of about 0.0017 pH (0.1 mV).
Two decimal place resolution is much preferred to 1 as it puts the quantizing noise at 0.003 pH which is well below the fundamental accuracy limitation of ±0.02 pH attainable with spanning (4 and 7) ±0.02 pH technical buffers. This represents good system design i.e. the instrument resolution contribution to inaccuracy is insignificant. For 0.1 pH resolution the quantizing noise is 0.03 - greater than the buffer limitation. This represents poor system design.
But this would be moot if we didn't need more than 1 decimal place accuracy but we do or at least benefit from it. One decimal digit with a cheap pH meter is better than the 0.5 decimal digit available from test strips but not as good as the implied 1.3 digits available from a meter with 0.05 pH accuracy (the limit I would recommend for brewing) which is in turn not as good as the 1.7 digits implied by a meter with resolution of 0.01 but accuracy of 0.02 as detemined by the buffers.
Now if your comment about chasing pH readings means that you are finding reading unstable in situations where the true pH is known to be stable (i.e. in a buffer at constant temperture). Then there is a problem with the meter and or electrode. Most commonly the problem is a clogged junction but as meters age their response slows especially in brewing where protein deposition is a potential problem. In low ionic strength situations electrical noise from static buildup/discharge can be a problem. There are solutions to all of these.
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