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General Category => Equipment and Software => Topic started by: beer_crafter on October 10, 2011, 05:54:55 PM

Title: How to use a pH meter
Post by: beer_crafter on October 10, 2011, 05:54:55 PM
Does anyone have a link to an article about how best to use a pH meter.  Looking specifically for best practices with respect to calibration, usage, and storage.
Title: Re: How to use a pH meter
Post by: euge on October 10, 2011, 06:42:36 PM
Depending on the type of meter you'll need the green 7.0 pH calibration fluid which also doubles as the storage solution. The storage solution should be discarded every couple of weeks depending on frequency of use. Only calibrate with fresh fluid, since the solution will drift in pH. When you turn on the meter while it is in the fluid don't be alarmed if it reads off if it has set for awhile. The meter still is calibrated- it's the fluid that is off.

Keep the probe clean after each use- clean the outside with a soft toothbrush, but be very gentle with the bulb part of the probe if this is the type you have- I recommend rinsing it thoroughly before and after taking readings and before storage.

Don't let the probe dry out and you should have worry free use for a long time.
Title: Re: How to use a pH meter
Post by: punatic on October 10, 2011, 08:20:41 PM
pH calibration buffers should not drift in pH.  They are designed specifically not to drift (that's why they are called buffers). 

pH meters do drift in pH.  That's why they need to be calibrated
Title: Re: How to use a pH meter
Post by: euge on October 10, 2011, 08:53:39 PM
pH calibration buffers should not drift in pH.  They are designed specifically not to drift (that's why they are called buffers). 

pH meters do drift in pH.  That's why they need to be calibrated

I've found that the storage solution in the cap will drift upwards due to dilution from extant moisture on the probe. Best to change the solution frequently and not rely on used storage solution for calibration. I calibrate if the clean meter shows signs it has drifted when placed in fresh solution.

Also, I have found a clear slime growing in the solution, obviously contaminated by the probe. This certainly throws off the pH of the solution. Solved that by cleaning the probe and cap thoroughly with everclear.  Teach me to measure garden soil pH with my brewing meter. Lol. I still use it to measure pH of fertilizers and such.
Title: Re: How to use a pH meter
Post by: James Lorden on October 10, 2011, 11:14:02 PM
The pH solution generally has a limited life I have seen it break down if kept to long. The last bottles I got from more beer had an expiration date that was much shorter then I expected it to be.
Title: Re: How to use a pH meter
Post by: mabrungard on October 11, 2011, 02:43:54 PM
Calibration within the range of interest is an important quality assurance measure when using a pH meter.  Since mashs are acidic, calibrating at the pH 4 and 7 points is most useful.  

Calibration solutions are composed primarily of water with buffering ions that stabilize the solution pH at the desired reference value.  Interaction with the atmosphere introduces CO2 and other contaminants that will cause the pH of the solution to drift.  Most calibration solutions are date stamped and they do have a finite lifespan after opening.  The time to pH drift is not well defined since it would depend on a lot of external factors.  I've heard that the solutions should be changed every year or two.  We aren't working with critical issues in mashing, so I feel that the longer timeframe is probably OK.  

Of course, keep the unused calibration solutions capped as much as possible and avoid cross contamination.  DO NOT immerse your pH probe into the bottle of calibration solution.  You want to avoid contaminating that supply.  Always pour a small amount into another small container for the calibration use.  Use separate small containers for each solution.  

This is not completely good advice, but I use the bottle caps from my pH solutions as the small containers for pH calibration.  I fill each cap with their respective solution and dip the probe into the solutions.  The probe is rinsed with DI or RO water after each immersion and I blow off the excess liquid by mouth prior to moving the probe from one solution or rinse to the other.  Don't touch the glass probe.  Its fragile and oils on skin can contaminate the probe.  The solution in the caps is discarded after each calibration event.  Never pour the used solution back into the bottle.  I shake out the bottle cap after discarding the spent solution, but clearly the opportunity for a little bit of contamination exists because that cap goes back on the bottle.

I don't think that pH calibration solutions should be used as probe storage solution.  They do not have the proper high Potassium concentration needed to keep the probe healthy.  You need to keep the probe in commercial storage solution or you need to create some.  I did use pH 4 solution as the starting point for storage solution I created.  You have to add a certain amount of potassium chloride to the pH 4 solution to create storage solution.  I don't remember what the ratio of KCl to solution was.  You'll have to google it.  

Always rinse the probe with distilled or RO water between every immersion in wort or water since there are plenty of contaminants or dissolved solids that could coat the probe.  I also suggest that occassionally dipping the probe in a strong acid and a strong base can help dissolve stubborn deposits.  

Enjoy.
Title: Re: How to use a pH meter
Post by: denny on October 11, 2011, 04:22:06 PM
Excellent info as always, Martin!  Thank you!
Title: Re: How to use a pH meter
Post by: bluesman on October 11, 2011, 04:44:37 PM
Calibration within the range of interest is an important quality assurance measure when using a pH meter.  Since mashs are acidic, calibrating at the pH 4 and 7 points is most useful.  

I believe it is also important to correct for temperature. Measuring the wort pH and compensating for it can be a significant factor in pH measurement accuracy.

Thoughts Martin?
Title: Re: How to use a pH meter
Post by: mabrungard on October 11, 2011, 06:35:35 PM
Indicated pH is dependent upon the temperature of the liquid.  In addition, there are other reasons why the user should standardize the temperature at which they perform their pH measurements. 

pH meters will register differently as the temperature of the liquid varies.  There are a couple of reasons why this occurs.  The first is the difference in how the meter and it's electrochemistry operate with temperature variation.  Manufacturers have incorporated temperature correction circuitry into higher-end meters to take care of that problem (temperature compensation).  That feature is helpful, but it DOES NOT correct for the change in mash pH due to differing chemical activity related temperature change.  The dissociation of ions in the mash varies with temperature and that creates an actual change in the mash pH.  That change is reported to be up to 0.35 standard units, but both Kai Troester and AJ DeLange have reported that they have only observed about a 0.2 standard unit difference.  In any case, the pH at mash temp will be lower than at room temperature. 

So even with a temperature-compensated pH meter,  you may not be reading the correct mash pH or getting a value that is useful.     

The other reason that brewers should avoid measuring mash pH at mashing temperature is that the high thermal stress placed on the probe's thin glass bulb.  Going from room temperature to mash temperature by plunging the probe into the mash will shorten the probe's life. 

For the reasons above, pH measurement for the mash should be done at room temperature.  There are fewer side effects in performing pH measurement at room temperature and it also means that you don't have to buy the more expensive temperature-compensated meter!
 
Title: Re: How to use a pH meter
Post by: James Lorden on October 11, 2011, 07:31:34 PM
Since the mash pH at room temperature should be higher then mash pH at mash temps do you know at what temperature level the common preferred mash pH levels are quoted. (e.g are we looking for 5.3 at room temp or 5.3 at mash temp).  I've always assumed 5.3 at mash temps so I look for about 5.5 for room temperature measurements.
Title: Re: How to use a pH meter
Post by: mabrungard on October 11, 2011, 08:38:20 PM
Since the mash pH at room temperature should be higher then mash pH at mash temps do you know at what temperature level the common preferred mash pH levels are quoted.

AJ DeLange has wondered aloud the same question: What were the mash temps used when those old brewing text references cited mash pH?  Neither of us know.  I can only imagine that it would be in the saccharification range (140s to 150s F).  Given that, the variation in pH within that range would be relatively small even if you assume the difference in room temp and mash temp pH was 0.35 units. (say 80F difference is to 0.35 units as 10F difference is to about 0.04 units).  Pretty small.
Title: Re: How to use a pH meter
Post by: punatic on October 11, 2011, 09:27:36 PM
Since the mash pH at room temperature should be higher then mash pH at mash temps do you know at what temperature level the common preferred mash pH levels are quoted.

AJ DeLange has wondered aloud the same question: What were the mash temps used when those old brewing text references cited mash pH?  Neither of us know.  I can only imagine that it would be in the saccharification range (140s to 150s F).  Given that, the variation in pH within that range would be relatively small even if you assume the difference in room temp and mash temp pH was 0.35 units. (say 80F difference is to 0.35 units as 10F difference is to about 0.04 units).  Pretty small.


Driving the mash pH down does increase the fermentability of the wort.  That acid malt addition probably was the culprit.  A couple tenths lower pH can have a substantial effect on fermentability. 

The 5.3 pH measured is at the lower end of where I prefer the mash to go.  I have had mashes at 5.2 and can assure you that the result was substandard for me...far too attenuated (the malt character was gone) and I could pick up a hint of sourness in the flavor profile.  Aim for 5.4 in your mash in most cases and you can bump that up a tenth if reduced fermentability is desirable. 

In my opinion, mash pH may be one of the final frontiers for tuning wort and beer performance.  Bru'n Water is the tool to use for figuring out that tuning adjustment.


Pretty small, but pretty significant nonetheless?
Title: Re: How to use a pH meter
Post by: beer_crafter on October 12, 2011, 07:15:43 PM
great tips y'all!
Title: Re: How to use a pH meter
Post by: gandelf on October 24, 2011, 11:05:54 PM
Thanks once again for the info Martin. I purchased a fancy Milwaukee temp compensating pH
meter a couple of years ago. I called a Milwaukee  tech to confirm the best procedure for calibrating
the new meter. The tech stated the same info as in Martins recommendation. He also included
this:
"To insure pH electrode longevity, insure test sample temperature is 60 to 80 F.
pH electrode condition test:
1.   Use Windex blue (11.2 factory fresh pH) as a test sample, at least 2” deep.
2.   Immerse pH electrode in Windex and note how fast a stable 10 pH plus is determined.
    New pH electrode, stable reading is almost instantaneous.
    Old ph electrode, stable reading takes 2 or 3 seconds.
    Standard pH electrode life expectancy is one year.
    Write replacement date with fine point Sharpie on pH electrode body."
Title: Re: How to use a pH meter
Post by: punatic on October 25, 2011, 04:43:13 AM
    New pH electrode, stable reading is almost instantaneous.
    Old ph electrode, stable reading takes 2 or 3 seconds.
   
Standard pH electrode life expectancy is one year.   

I think you were talking to a salesman.  pH probes can and do last much longer than 1 year with proper care and maintenance. 

Instantaneous and 2 - 3 second readings depend on your meter. I have a pH meter that allows you to select how long to measure and how many readings are averaged into the locked in value for the pH of the sample.

If you notice that your readings are taking longer to stabilize than they did when the probe was new, soak the probe overnight in a mild citric acid solution to remove scale that has formed on the probe's electrodes.  You can buy citric acid in crystalline form at your LHSS.
Title: Re: How to use a pH meter
Post by: Pinski on March 23, 2012, 03:28:45 PM
I bought a pH meter last night and was reading some past posts to prepare to use it next week, great discussion here. So I think the biggest questions I have are... At what points in the mash process should samples be taken and tested and if necessary, adjustments made?  At what point do you stop sampling/adjusting? Pre-boil? Pre-pitch?
Title: Re: How to use a pH meter
Post by: Hokerer on March 23, 2012, 03:33:09 PM
I bought a pH meter last night and was reading some past posts to prepare to use it next week, great discussion here. So I think the biggest questions I have are... At what points in the mash process should samples be taken and tested and if necessary, adjustments made?  At what point do you stop sampling/adjusting? Pre-boil? Pre-pitch?

The only time I really check/worry about pH is at the beginning of the mash.  Mash in and give it a little time to settle and then check the pH.  Add whatever that reading tells you that you need to add, give it a little more time and check the pH again to see that your additions did what you expected.
Title: Re: How to use a pH meter
Post by: brewmichigan on March 23, 2012, 05:06:43 PM
Martin I hope you save all this info in a word doc or something so you just cut and paste when someone else asks a similar question in the future. I'd hate to write all that down all the time. Very good info indeed!
Title: Re: How to use a pH meter
Post by: redzim on March 24, 2012, 12:20:25 PM
Can anyone recommend to me a decent pH meter that they use?  I have been using a Milwaukee MW102 for a year and sadly it does not seem consistent. Drifts all over the place even in buffers.  I just sent it in to the factory, they replaced the temp probe and and returned it to me but it still does wierd stuff like this: you calibrate it in 7.01 buffer, then in 4.10 buffer, and if you leave it in the 4.01 buffer, within 1 minute it is reading 3.85 or 3.90....  or if, after calibration, you measure a sample of mash, vinegar or windex, then rinse the probe and put it back into the 4.01 buffer, it can read anywhere from 3.60  to 4.20... but certainly not right around 4.01....

Anyone have a better manufacturer to recommend to me? I'm getting a little fed up with Milwaukee... I'm on the phone with their techs about every brew session lately.... or can anyone tell if I am doing something wrong?

-red
Title: Re: How to use a pH meter
Post by: euge on March 24, 2012, 05:21:18 PM
Hanna instruments are available everywhere and are reliable: http://www.hannainst.com/usa/subcat.cfm?id=002 (http://www.hannainst.com/usa/subcat.cfm?id=002)
Title: Re: How to use a pH meter
Post by: redzim on March 24, 2012, 07:01:11 PM
Hanna instruments are available everywhere and are reliable: http://www.hannainst.com/usa/subcat.cfm?id=002 (http://www.hannainst.com/usa/subcat.cfm?id=002)

what model do you use?
Title: Re: How to use a pH meter
Post by: euge on March 24, 2012, 07:10:27 PM
Hanna instruments are available everywhere and are reliable: http://www.hannainst.com/usa/subcat.cfm?id=002 (http://www.hannainst.com/usa/subcat.cfm?id=002)

what model do you use?

Hanna Champ HI98106 for around $30

Manual calibration but that is a plus! And extremely easy to do. I'll only go with manual calibrating meters from now on.
Title: Re: How to use a pH meter
Post by: Pinski on March 24, 2012, 08:19:08 PM
My model is the 98018. I'll take it for a spin on three batches this week and report back.
Title: Re: How to use a pH meter
Post by: narvin on March 25, 2012, 02:51:01 AM
Did they try replacing the probe?  I have the MW 102 and haven't really had any problems with it.  When you see the hour glass go away, you should be able to take a reading.  It may drift a little after that, but not by as much as you're seeing.  You should be moving the probe around slowly as you take the reading;  otherwise, diffusion from the probe can affect the sample directly in contact with it.

I pulled mine out of the storage solution after a month and the 4.01 solution reading was dead on, and the 7.01 read around 6.98.
Title: Re: How to use a pH meter
Post by: ccfoo242 on March 26, 2012, 06:05:08 PM
This one looks sweet: http://www.amazon.com/Extech-PH100-ExStik-Waterproof-Meter/dp/B00023RYQ8/ref=sr_1_1?ie=UTF8&qid=1332784821&sr=8-1

(http://ecx.images-amazon.com/images/I/31MM1D90S1L._SL500_AA300_.jpg)


$90....I guess I could skip lunch for a few weeks to pay for it!  ;D
Title: Re: How to use a pH meter
Post by: redzim on March 29, 2012, 06:53:51 PM
Did they try replacing the probe?  I have the MW 102 and haven't really had any problems with it.  When you see the hour glass go away, you should be able to take a reading.  It may drift a little after that, but not by as much as you're seeing.  You should be moving the probe around slowly as you take the reading;  otherwise, diffusion from the probe can affect the sample directly in contact with it.

I pulled mine out of the storage solution after a month and the 4.01 solution reading was dead on, and the 7.01 read around 6.98.

I got to Milwaukee tech support again today and they agree that my meter seems flaky. They are going to replace it free of charge so we'll see if that helps.

Title: Re: How to use a pH meter
Post by: nateo on March 29, 2012, 07:28:35 PM
I've been getting some odd readings on my Hanna HI 98107 (the 2-point calibration one). I read the label on my buffer solutions, and it said not to pour the used solution back into the bottle. D'oh! I've been doing that for the past year or so.

I've ordered some new buffers, but I wonder which direction the old solution would push the pH, up or down? 

Title: Re: How to use a pH meter
Post by: mabrungard on March 29, 2012, 07:45:10 PM

I got to Milwaukee tech support again today and they agree that my meter seems flaky. They are going to replace it free of charge so we'll see if that helps.

I've had the Hanna meters for years and they are alright.  I recently moved to Milwaukee meters and am pleased.  I use the MW-101 and it works very well.  Hopefully this replacement will solve your problems.
Title: Re: How to use a pH meter
Post by: punatic on March 30, 2012, 12:56:46 AM
I've been getting some odd readings on my Hanna HI 98107 (the 2-point calibration one). I read the label on my buffer solutions, and it said not to pour the used solution back into the bottle. D'oh! I've been doing that for the past year or so.

I've ordered some new buffers, but I wonder which direction the old solution would push the pH, up or down?

As a rule in bench chemistry, one should never return excess chemicals to the original container once they have been removed from the original container.  This is to avoid contaminating the entire container.

That said; they are called buffers because they are made specifically to resist pH change.  I wouldn't be too overly concerned with the buffers not maintaining their stated pH value.  Unless you contaminated the portion that you removed and returned, e.g. with rinse water from rinsing the pH probe off.
Title: Re: How to use a pH meter
Post by: nateo on March 30, 2012, 02:48:34 PM
Unless you contaminated the portion that you removed and returned, e.g. with rinse water from rinsing the pH probe off.

That's what I'm afraid happened. My tap water is really alkaline, so maybe if half a ml of rinse water contaminated it each time I calibrated it, after a long time that could skew the samples. When my new buffers show up I'll compare the results.
Title: Re: How to use a pH meter
Post by: madscientist on March 30, 2012, 02:59:45 PM
I'd imagine you could make a storage solution from NuSalt (potassium Chloride instead of sodium chloride) for a storage solution.
Title: Re: How to use a pH meter
Post by: punatic on March 30, 2012, 05:31:17 PM
Unless you contaminated the portion that you removed and returned, e.g. with rinse water from rinsing the pH probe off.

That's what I'm afraid happened. My tap water is really alkaline, so maybe if half a ml of rinse water contaminated it each time I calibrated it, after a long time that could skew the samples. When my new buffers show up I'll compare the results.

Write back with what you find.  It will be interesting to see.  I'm guessing the contaminated buffers will be unchanged.  Good idea to buy new buffers though.
Title: Re: How to use a pH meter
Post by: nateo on April 03, 2012, 11:52:38 PM
My new calibration solutions came today. My old calibration solutions were definitely contaminated, I assume from rinse water.
New solution > Old solution
7 > 7.2
4 > 4.4
10 > 10

I didn't use the 10pH solution as often as the other two. So, word of warning. I thought my funky readings meant my meter was busted, but it was just that the solutions were off.
Title: Re: How to use a pH meter
Post by: oceanselv on April 04, 2012, 12:18:07 AM
After reading the thread I noticed one piece of advice that has not been given.  The probe should never be wiped with a lab wipe or any thing similar, IE a kimwipe.  Instead gently pat the probe with a damp lab wipe.   Wiping the probe down creates a static charge which can affect the pH of the solution being measured.
Title: Re: How to use a pH meter
Post by: mabrungard on April 04, 2012, 11:57:46 AM
I don't ever wipe the bulb on my pH probe.  The whole probe gets a distilled or RO rinse and then I blow out the droplets by mouth.  I suppose it would be even better to blow it off with compressed air, but its not like I'm spitting on it.  The blowing gets the droplets out from around the protected bulb area.  Then I can use a regular paper towel on the exterior of the probe housing to absorb those droplets.  It usually takes a couple of blows and wipes to get the bulb and probe dry.
Title: Re: How to use a pH meter
Post by: bo on April 04, 2012, 12:21:01 PM
Can you store them with the probe immersed in distilled water?
Title: Re: How to use a pH meter
Post by: jmcamerlengo on April 04, 2012, 03:57:29 PM
Can you store them with the probe immersed in distilled water?

I've heard that this is bad practice.
Title: Re: How to use a pH meter
Post by: nateo on April 04, 2012, 04:54:36 PM
I've heard that this is bad practice.

Yeah distilled water is corrosive. Storage solutions contain salts that will extend probe life.
Title: Re: How to use a pH meter
Post by: oceanselv on April 04, 2012, 05:55:01 PM
Storage solutions are indeed best to store the probes in.  As for drying the probe, there is no need to completely dry the probe. As a bench chemist for 20 years, I have found a good rinse with distilled water and then a very gentle pat down with a paper towel will work fine.  This will not induce a much of a static charge.  I wouldn't use compressed air from a compressor to dry the probe as the compressed air typically has a small amount of compressor oil trapped in it.   Also be careful of blowing on the probe to dry it as our breath also has saliva in it.
Title: Re: How to use a pH meter
Post by: mabrungard on April 04, 2012, 07:03:31 PM
Can you store them with the probe immersed in distilled water?

No.  The probe is filled with a ion-saturated (typically potassium) solution or gel.  Its important to keep that solution saturated with that ion.  The glass probe is actually permeable.  Immersing the probe in a solution with very low ionic strength creates an osmotic pressure that draws those ions out of the probe and into the exterior solution.  You end up depleting the ion solution inside the probe.  pH probe storage solutions are typically high in the particular ion and when the probe is immersed in that solution, then there is not the osmotic stress drawing ions out of the probe.  The probe solution stays saturated.
Title: Re: How to use a pH meter
Post by: punatic on April 04, 2012, 10:20:41 PM
Yes, probe storage solution is the best way to store your pH probe.

However, if you only have a choice of distilled (deionized) water or leaving the probe in the air to dry out, choose keeping the probe wet.  Allowing it to dry out will ruin the probe quickly.  Parking the probe in deionized water for a few hours to keep it from drying out will not cause problems.  Parking it in a pH buffer temporaily is a better option still.
Title: Re: How to use a pH meter
Post by: redzim on May 10, 2012, 01:33:00 PM
Did they try replacing the probe?  I have the MW 102 and haven't really had any problems with it.  When you see the hour glass go away, you should be able to take a reading.  It may drift a little after that, but not by as much as you're seeing.  You should be moving the probe around slowly as you take the reading;  otherwise, diffusion from the probe can affect the sample directly in contact with it.

I pulled mine out of the storage solution after a month and the 4.01 solution reading was dead on, and the 7.01 read around 6.98.

I got to Milwaukee tech support again today and they agree that my meter seems flaky. They are going to replace it free of charge so we'll see if that helps.

I have to give a big +1 to Milwaukee on this one; after a lot of tech calls they agreed to replace the entire meter and probes for free. I must have had a lemon, because the replacement I got has been much more solid; it calibrates a lot quicker (2-3min vs 8-10min) and hardly drifts at all in samples (maybe 0.1pH over a couple minutes max). Also holds its calibration nicely, when I haven't used it for a few weeks I check it in a 4.01 buffer before recalibrating and it is always between 3.98 and 4.04. Which my old meter never was....  so although Milwaukee's QA on their product line might not be the best, their customer service is nice.
-red