Mash Temp at Room Temperature

[Yorg]

A google gave me conflicting information on the question of the right Ph reading at room temperature.
Two Questions:
1/
If I cool a sample of my mash to get it to room temperature, or within the automatic temperature compensation range of my Ph meter, is the Ph I want to see around 5.2-5.3 or around 5.5-5.6?
2/
If using a Ph strip (not a digital meter, but the paper), given that it would cool very rapidly once dipped, what is the desired reading?

 

[jagg]

A google gave me conflicting information on the question of the right Ph reading at room temperature.
Two Questions:
1/
If I cool a sample of my mash to get it to room temperature, or within the automatic temperature compensation range of my Ph meter, is the Ph I want to see around 5.2-5.3 or around 5.5-5.6?
2/
If using a Ph strip (not a digital meter, but the paper), given that it would cool very rapidly once dipped, what is the desired reading?

I think anything from 5.2 to 5.6 will be fine , I dont think the temp of the sample would make any difference, someone correct me if Im wrong.

 

[Gremlyn]

Temp of the sample does matter for digital probes, I can't remember if the strips have a range of temp for accuracy. As the OP said, the probe can adjust for temp to an extent. I saw cool a small sample, maybe stick it in the freezer for a short time, and you'll be good to go.

 

[Yorg]

After chewing this one over on the Australian site, it might surprise some to know that when you use a PH meter, you should be looking for a reading of 5.5 not 5.2.
You see, the Automatic Temperature Compensation allows you to take a reading within a range, as if you had cooled the sample to room temperature.
At room temperature the PH reading you need on the meter is 5.5, equivalent to 5.2 at Mash Temp.

I bet a few people are labouring under a misconception here - I know I was.

Begging the question, how does the 5.2 product from 5 Star work. Anyone use it and also take a reading?

 

[Kaiser]

The title should read "Mash pH at room temperature".

You see, the Automatic Temperature Compensation allows you to take a reading within a range, as if you had cooled the sample to room temperature.

At room temperature the PH reading you need on the meter is 5.5, equivalent to 5.2 at Mash Temp.

That's what I thought too until I looked at the problem a little closer:

The pH of a solution changes with its temperature. This pH shift is real and it results from the greater disassociation of H+ ions at higher temperatures. As a result the pH of a hot solution is lower than the pH of a cold solution. But this temperature dependent pH change is also substrate dependent. For wort it is generally known that the pH at mash temps (150F) is about 0.35 units lower and at mash-out temps (170F) it is about 0.45 units lower.

A pH meter probe generates a voltage on its terminals depending on the H+ concentration (pH) and the temperature. But this temperature dependence is a property of the pH electrode and will be the same for all the substrates that can be tested. This is also the temperature dependence that the ATC function of a pH meter compensates for.

So when you use an ATC pH meter you can measure the true pH of a solution at various temperatures. This included the pH shift based on substrate temperature. I.e. if you measure wort with that pH meter at 160F and at 70F you will notice that the pH reading at 160F is 0.35 units lower than the one at 70F.

But in order to extend the life of the probe it is recommended to use pH meters on cooled samples only. I have a ATC pH meter but I calibrate and test always at 25C. That means I cool wort samples to 25C and warm up beer to 25C. I do that b/c I don’t know the exact relationship between temperature and pH for these substrates. By having one reference temp (25C) I don’t have to worry about this.

Most pH measurements given in the literature are room temp pH values. When it comes to mash pH, the proper room temp target is 5.3-5.7 with the optimum being around 5.55. Don’t worry about what the pH at mash temp is since it is not recommended to measure it at that temp.

I don’t know as much about strips. I only know that the manufacturer recommends using them on a cooled sample. They are based on a dye that changes color based on H+ concentrations. Which makes me believe that they would change color as they cool when they are pulled out of the hot mash. But I have not observed that yet.

Kai