pH and Temperature Correction

[Spine]

Hello Everyone. On the weekend made and AG batch and this was my first batch in which I tried removing some of the carbonate/bicarbonate with some phosphoric acid. I added the acid (70% solution) directly to the mash with a dropper and stirred well and measured the pH.

The pH seemed to want to hang around 5.00 at mash temperature ~150dF. When I took the same sample and cooled it to ~60dF the reading was 5.19.

This makes me believe that my pH meter does not to any sort of temperature compensation.

SO, when everyone says (including enzyme charts) that the pH should be around 5.2-5.4 is this at MASH temperature or room temperature?

If the pH meter has temperature compensation, does this mean it will give you the reading of the sample if it were at room temp?

I'm confused!

 

[WBC]

Room temperature.

Water Frequently Asked Questions - Midwest Homebrewing and Winemking Supplies



Measuring PH: pHMeters - ISFET - Application Notes

http://www.eseasongear.com/hahipophtehi.html

 

[Kaiser]

This is what I answered Spine when he asked me this question via PM:

There are 2 things that affect the pH reading of a meter: How the temperature affects the response of the electrode and how the temperature changes the pH of the solution. The first one has something to do with the meter and the 2nd one is real. For mashing it is known that the pH at mash temps is about 0.35 units lower than that of a mash sample at room temp.

What the temp correction of a meter does is to compensate for the temp effect on the electrode meaning that you can measure pH at a temperature other than the calibration temp (which is 25 C as the buffer solutions are calibrated at that temp). So with your meter you can only measure at 25C unless you correct for temp yourself. There must be a formula for this somewhere but I recommend sticking with 25C measurements. That's what I do as well and I have a temp correcting pH meter.

So the range you are looking for at this temp is 5.4 - 5.7

I hope that helps. I'll have a look at the thread later. This is a confusing subject but once you understand what pH meter temp correction does and what happens with the pH of the wort as the temp changes it will become more clear.


Kai

 

[Bru]

Can someone please clarify - if mash pH is supposed to be between 5.4 and 5.7 at 25C, what should the pH meter read at mash temps ?
Im never sure whether to compensate pH up or down when the mash is at 67degC.

 

[Kaiser]

Can someone please clarify - if mash pH is supposed to be between 5.4 and 5.7 at 25C, what should the pH meter read at mash temps ?

Many will say that the pH of the hot mash is 0.35 units lower (i.e. you would read 5.05 - 5.35) but my experience and other's who have actually compared the two pH meter reaings show a difference of only 0.2 units (i.e. you would read 5.2 - 5.5).

But unless you want to replace your probe more often, don't test the hot mash.

Kai

 

[Bru]

Thanks Kaiser - good point on the probe.

 

[GrowlerMonkey]

Waking up a pretty old thread. Any idea how to tell when your probe should be replaced. I've had mine for about 6 months and have probably tested 10 batches, all at mash temps :-/

Also, to get the temp of the sample down quickly, are you guys just using a small ice bath?

Thanks!

 

[GotPushrods]

Waking up a pretty old thread. Any idea how to tell when your probe should be replaced. I've had mine for about 6 months and have probably tested 10 batches, all at mash temps :-/

Also, to get the temp of the sample down quickly, are you guys just using a small ice bath?

Thanks!

I keep some heavy coffee mugs in the deep freezer. I sample about half a shot glass, and pour that into the mug. A few swirls and it's cooled VERY quickly.

 

[acidrain]

I keep some heavy coffee mugs in the deep freezer. I sample about half a shot glass, and pour that into the mug. A few swirls and it's cooled VERY quickly.

That is a great idea!

GrowlerMonkey, when your meter won't calibrate, or when it wanders all over the place, it needs to be replaced.