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Old 01-18-2011, 06:55 PM   #1
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Default Got a new (my first) meter and had a couple of newbie questions

I got a pH meter for Christmas. Milwaukee. Automatic temperature adjusting. I don't have the model handy as I am writing this from work. I went ahead and invested in the full bottles of 4.01 and 7.01 calibrating solutions. I also bought a bottle of the probe storage solution.

I have not read through the manual yet as I have not had a chance to brew with it yet (will this coming weekend, though). I am assuming that the calibration will be explained in the manual and just uses a small amount of each solution.

I did have a couple of other questions about use and storage for brewing purposes:

1. Probe storage in the solution. Is it as simple as storing the probe upright with the cap filled with the storage solution?

2. Do I need to check the cap every so often to ensure the solution has not evaporated or leaked? (I only have a chance to brew every 4-5 weeks)

3. Can the solution be re-used or does it need to be changed every time I use and re-store the probe?

4. Should I rinse it with something before I take a pH reading of my mash sample? I won't be returning the sample to the mash but wanted to ensure that the storage solution didn't interfere with the reading

5. How large a mash sample should I take?

6. Should the sample be grains only? Liquid only? A mix of both?

7. It says the meter will automatically correct for temperature, but is there a limit to this? Should I let the mash cool to below 100F before I take a reading?

Thanks in advance for any help you guys can offer

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Old 01-18-2011, 07:25 PM   #2
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1. Probe storage in the solution. Is it as simple as storing the probe upright with the cap filled with the storage solution?
Yes

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2. Do I need to check the cap every so often to ensure the solution has not evaporated or leaked? (I only have a chance to brew every 4-5 weeks)
Yes - probably doesn't have to be every week or even every month. It depends on how tight the cap fits. You don't want to let the electrode go dry though it isn't the end of the world if you do. You will be initiated into the intriguing world of "potassium chloride creep" in which crystals of this will work their way out around the cap no matter how tight it is.


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3. Can the solution be re-used or does it need to be changed every time I use and re-store the probe?
It can be reused. You don't want it to become too dilute. You will carry water into the solution each time you replace the cap because you will have rinsed the electrode before putting the cap back on. A shake and/or a blot with paper towel helps to soak up much of this rinse water.

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4. Should I rinse it with something before I take a pH reading of my mash sample? I won't be returning the sample to the mash but wanted to ensure that the storage solution didn't interfere with the reading
Yes. You should rinse the electrode with DI water whenever you move it from one solution to another i.e. you rinse it when moving from the storage solution to the first buffer, when going from the first buffer to the second, from the second buffer to the sample, from the sample back to the storage solution....

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5. How large a mash sample should I take?
Just enough to cover the business end of the probe.


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6. Should the sample be grains only? Liquid only? A mix of both?
You are measuring the pH of the liquid so just be sure that if there is grain material in there that the mix is "loose". It isn't necessary to try to get liquid only. Where grain is involved be sure to "blast" it loose with a squirt of DI water when coming out of the sample.

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7. It says the meter will automatically correct for temperature, but is there a limit to this?
If the "isoelectric pH" of the electrode is outside the region 6.5 < pHi < 7.5 ATC introduces errors because modern meters all assume that pHi = 7. This shouldn't be something you need to worry about but I mention it because I have an electrode whose pHi is outside this range.

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Should I let the mash cool to below 100F before I take a reading?
Absolutely. You should allow the sample to cool to room temperature as this will extend electrode life appreciably and that is the main reason for doing this. A secondary reason is that if buffers and samples are all measured at the same temperature it doesn't matter where pHi falls i.e. ATC doesn't do anything and cannot, therefore, screw up a reading because of pHi.
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Old 01-18-2011, 08:00 PM   #3
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Thanks AJ. Your answer to #4 brought up another question. Should I re-calibrate every time I brew? If now, how often would you recommend recalibrating?

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Old 01-18-2011, 08:07 PM   #4
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Yes, absolutely. I've had an electrode stay in cal for a couple of months but that is a remarkable and rare occurrence. Some like to calibrate before commencement of a measurement sequence (such as a brew day) and then do a cal check at the end. A good cal check after the fact assures you that the measurements you got were good.

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Old 01-18-2011, 08:39 PM   #5
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How long do electrodes typically last if all samples are kept under 80*

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Old 01-18-2011, 09:21 PM   #6
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How long do electrodes typically last if all samples are kept under 80*
I've been getting better than 2 years on modern electrodes.
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Old 01-18-2011, 10:35 PM   #7
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How do you know when the electrodes are going bad?


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Old 01-19-2011, 03:46 AM   #8
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The first thing you usually notice is that the response is slowing. In particular, when you calibrate you start in (typically) pH 7 buffer, wait for stabilization, enter the pH 7 cal, rinse and place the electrode in pH 4 buffer and wait for stabilization again. Many modern meters determine stabilization for you (by noting the change in mv over time) but however it is done a new electrode might be able to be calibrated in a minute whereas one that is aging may take 2, 3 or even more. It is not a day and night thing. Aging is gradual and often one swaps out an electrode that still has life in it simply because he gets tired of waiting. A pH electrode has a slope (the amount it's response changes per unit change in pH) and offset (the voltage it produces in pH 7 buffer). The former should be -58.17 mv/pH at 20 °C and the latter 0. The purpose of a cal is to measure slope and offset and most modern meters display and even record these parameters at each calibration. As the electrode ages the slope will become smaller in magnitude and the offset will increase. Again this is a gradual thing. Some meters will not calibrate (i.e. become unusable) when the slope drops below 90% of the value it should have (depends on temperature). This forces the operator to install a new electrode (and helps the manufacturer sell them). So the simple answer to the question is that when response slows, slope declines and offset increases it is time to think about replacement. Rejuvenation is possible with some electrodes to some extent. In brewing, for example, coating of the bulb with protein will slow response. Cleaning the protein off with an enzymatic cleaner will restore rapid response.

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Old 01-19-2011, 11:18 PM   #9
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I use a an electrode pH meter for my job to screen soil (another great use for your meter if you want a really green lawn) and we just store the electorde with distilled water which has no ill effects. If you have cheap and easy access to DI water go for it but I wouldn't say its essential. I calibrate my meter once or twice a month, but then again I use it everyday. I reuse the buffer solution until it becomes cloudy then discard. If I was using it to for mashing I would probably calibrate before hand because beer is way more important the soil! Good luck.

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Old 01-20-2011, 03:41 AM   #10
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Do not store your electrode in DI water unless the manufacturer recommends DI water. The instructions that come with most electrodes specifically caution against storage in DI water or pH 7 buffer. Use the storage solution that the manufacturer recommends which is usually a solution of potassium chloride.

In brewing small pH changes can have large significance. We are looking for the best accuracy we can get. It is quite possible to get accuracy of around 0.02 pH using technical buffers but you must:

1. Store the electrode properly
2. Calibrate each time the meter is used (this means each brew day - not for each measurement during a brew day)
3. Use fresh buffers for each calibration
4. Rinse the electrode with DI water between storage solution and buffer, between buffers and between buffer and sample
5. Blot excess rinse water from the electrode before putting into buffers, storage solution, and sample (prevents them from getting diluted)

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