Author Topic: How to use a pH meter  (Read 6813 times)

Offline beer_crafter

  • Assistant Brewer
  • ***
  • Posts: 162
  • Hoppin' the hell out of the place since 1995
    • View Profile
How to use a pH meter
« on: October 10, 2011, 10:54:55 AM »
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.

Offline euge

  • Official Poobah of No Life.
  • *
  • Posts: 7225
  • Estilo Casero
    • View Profile
Re: How to use a pH meter
« Reply #1 on: October 10, 2011, 11:42:36 AM »
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.
The first principle is that you must not fool yourself, and you are the easiest person to fool. -Richard P. Feynman

Offline punatic

  • Official Poobah of No Life.
  • *
  • Posts: 4582
  • Puna District, Hawaii Island (UTC -10)
    • View Profile
Re: How to use a pH meter
« Reply #2 on: October 10, 2011, 01:20:41 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
There is only one success: to be able to spend your life in your own way.


AHA Life Member #33907

Offline euge

  • Official Poobah of No Life.
  • *
  • Posts: 7225
  • Estilo Casero
    • View Profile
Re: How to use a pH meter
« Reply #3 on: October 10, 2011, 01:53:39 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.
The first principle is that you must not fool yourself, and you are the easiest person to fool. -Richard P. Feynman

Offline James Lorden

  • Brewer
  • ****
  • Posts: 337
  • Forest Hill, MD
    • View Profile
Re: How to use a pH meter
« Reply #4 on: October 10, 2011, 04:14:02 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.
James Lorden
Beer Drinker Beer Maker & Beer Judge

Offline mabrungard

  • Senior Brewmaster
  • ******
  • Posts: 1097
    • View Profile
    • Bru'n Water
Re: How to use a pH meter
« Reply #5 on: October 11, 2011, 07:43:54 AM »
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.
« Last Edit: October 11, 2011, 07:47:07 AM by mabrungard »
Martin B
Carmel, IN

BJCP National
Foam Blowers of Indiana (FBI)

Brewing Water Information at:
https://sites.google.com/site/brunwater/

Like Bru'n Water on Facebook for occasional discussions on brewing water and Bru'n Water

Offline denny

  • Administrator
  • I must live here
  • *****
  • Posts: 11665
  • Noti OR [1991.4, 287.6deg] AR
    • View Profile
    • Dennybrew
Re: How to use a pH meter
« Reply #6 on: October 11, 2011, 09:22:06 AM »
Excellent info as always, Martin!  Thank you!
Life begins at 60.....1.060, that is!

www.dennybrew.com

The best, sharpest, funniest, weirdest and most knowledgable minds in home brewing contribute on the AHA forum. - Alewyfe

Offline bluesman

  • Global Moderator
  • I must live here
  • *****
  • Posts: 8678
  • Delaware
    • View Profile
Re: How to use a pH meter
« Reply #7 on: October 11, 2011, 09:44:37 AM »
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?
Ron Price

Offline mabrungard

  • Senior Brewmaster
  • ******
  • Posts: 1097
    • View Profile
    • Bru'n Water
Re: How to use a pH meter
« Reply #8 on: October 11, 2011, 11:35:35 AM »
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!
 
Martin B
Carmel, IN

BJCP National
Foam Blowers of Indiana (FBI)

Brewing Water Information at:
https://sites.google.com/site/brunwater/

Like Bru'n Water on Facebook for occasional discussions on brewing water and Bru'n Water

Offline James Lorden

  • Brewer
  • ****
  • Posts: 337
  • Forest Hill, MD
    • View Profile
Re: How to use a pH meter
« Reply #9 on: October 11, 2011, 12:31:34 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.
James Lorden
Beer Drinker Beer Maker & Beer Judge

Offline mabrungard

  • Senior Brewmaster
  • ******
  • Posts: 1097
    • View Profile
    • Bru'n Water
Re: How to use a pH meter
« Reply #10 on: October 11, 2011, 01:38:20 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.
Martin B
Carmel, IN

BJCP National
Foam Blowers of Indiana (FBI)

Brewing Water Information at:
https://sites.google.com/site/brunwater/

Like Bru'n Water on Facebook for occasional discussions on brewing water and Bru'n Water

Offline punatic

  • Official Poobah of No Life.
  • *
  • Posts: 4582
  • Puna District, Hawaii Island (UTC -10)
    • View Profile
Re: How to use a pH meter
« Reply #11 on: October 11, 2011, 02:27:36 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?
There is only one success: to be able to spend your life in your own way.


AHA Life Member #33907

Offline beer_crafter

  • Assistant Brewer
  • ***
  • Posts: 162
  • Hoppin' the hell out of the place since 1995
    • View Profile
Re: How to use a pH meter
« Reply #12 on: October 12, 2011, 12:15:43 PM »
great tips y'all!

Offline gandelf

  • Assistant Brewer
  • ***
  • Posts: 103
  • Mill Creek Brewery, Temptation Rd
    • View Profile
Re: How to use a pH meter
« Reply #13 on: October 24, 2011, 04:05:54 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."
Religion; A contrived security blanked for a species that is currently in its adolescent phase of its evolutionary journey.

Offline punatic

  • Official Poobah of No Life.
  • *
  • Posts: 4582
  • Puna District, Hawaii Island (UTC -10)
    • View Profile
Re: How to use a pH meter
« Reply #14 on: October 24, 2011, 09:43:13 PM »
    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.
There is only one success: to be able to spend your life in your own way.


AHA Life Member #33907