[banjo-guy]

I’ve been relying on Bru’n Water instead of a meter for my ph targets. I measure carefully and have a recent water report. How accurate and consistent are the ph calculations when compared to actual ph readings from a meter?

[Robert]

They do vary a wee bit.  Sometimes dead on, but always within 0.1 of predicted (I'm usually, if anything,  just a little lower than predicted, never higher.)  I believe the differences can be attributed to my imperfect measurement of salts or acids, inevitable batch to batch variations in malt, and just when the sample is pulled, not any inherent inaccuracy in Bru'n Water. IME it's as accurate as my measurements, or more so!

[apple]

I find that mine can vary by up to 0.2. Unlike Robert I'm usually high not low. In some cases I have been able to explain the difference due to mistakes in entering the grain bill. Other times I'm not sure what happened. For a while I was trying to use saurmalz. That was hard to predict the affect of. Lately I've tended to be within 0.1, which I say is close enough for me.

I think it would be difficult to know if your mash is truly on or not without a meter. I'm a big believer in Bru'n Water, but there are so many variables in all of our processes and ingredients that the only way to know is to actually test.

[hackrsackr]

I find that mine can vary by up to 0.2. Unlike Robert I'm usually high not low. In some cases I have been able to explain the difference due to mistakes in entering the grain bill. Other times I'm not sure what happened. For a while I was trying to use saurmalz. That was hard to predict the affect of. Lately I've tended to be within 0.1, which I say is close enough for me.

I think it would be difficult to know if your mash is truly on or not without a meter. I'm a big believer in Bru'n Water, but there are so many variables in all of our processes and ingredients that the only way to know is to actually test.

Hardness and alkalinity of your source water can also vary (unless using RO). If these parameters differ from your inputs, the residual alkalinity will be different, and the prediction will be skewed by the difference


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[Robert]

I find that mine can vary by up to 0.2. Unlike Robert I'm usually high not low. In some cases I have been able to explain the difference due to mistakes in entering the grain bill. Other times I'm not sure what happened. For a while I was trying to use saurmalz. That was hard to predict the affect of. Lately I've tended to be within 0.1, which I say is close enough for me.

I think it would be difficult to know if your mash is truly on or not without a meter. I'm a big believer in Bru'n Water, but there are so many variables in all of our processes and ingredients that the only way to know is to actually test.

Hardness and alkalinity of your source water can also vary (unless using RO). If these parameters differ from your inputs, the residual alkalinity will be different, and the prediction will be skewed by the difference


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Good points.  I build from RO and use simple grain bills with well known malts, which probably helps explain my consistency.  And I do still use a meter, as I track pH through boil and fermentation.

[banjo-guy]

I’ve been holding off buying a meter. Maybe it’s time get a ph meter.


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[mabrungard]

pH meters are a 'nice to have' element in your brewing equipment, but they do introduce a bit more effort to your brew day. I find that it adds at least another 5 minutes of prep time for checking calibration (or several minutes of frantic calibration when you forgot to do it beforehand and that sample is waiting). In addition, you'll be pulling and measuring extra samples during the mash (but I don't really have much else to do during the mash...so no big deal).

I wish that a pH prediction was spot on every time, but that will never happen. There are just too many variables that are beyond our control. The surest way would be to perform a mini mash and observe its pH and adjust from there in the full-scale mash. But that is certainly a serious PITA that I can't bring myself to do. Using software like Bru'n Water to get me in the ballpark with respect to mash pH, is good enough for me. But I still rely on my calibrated pH meter to help illustrate when the prediction varied from reality, which helps me bias my target pH for other similar brews. Measurement and experience help me get closer to my target. The only question remaining is: Was my target appropriate in the first place?

As we should all understand, there isn't a 'best' pH. Only good, better, and bad. Everything is a compromise in brewing.

[apple]

mabrungard, this makes me remember something I thought would be useful in the spreadsheet.

On a few occasions I've found my mash off enough that I felt compelled to adjust PH during the mash. I would usually reach for acid, and sometimes some baking soda.

I was able to calculate the approximate dosage rate by tweaking the values in my water additions. It would be great to have another section at the bottom of the adjustments page that lets me do a correction calculation. That way I could keep my original adjustments as a reference for next time as well as keep track of how far off I was. This would help me start to figure out if I am trending in some direction or if I just have a one off variation.

[hackrsackr]

mabrungard, this makes me remember something I thought would be useful in the spreadsheet.

On a few occasions I've found my mash off enough that I felt compelled to adjust PH during the mash. I would usually reach for acid, and sometimes some baking soda.

I was able to calculate the approximate dosage rate by tweaking the values in my water additions. It would be great to have another section at the bottom of the adjustments page that lets me do a correction calculation. That way I could keep my original adjustments as a reference for next time as well as keep track of how far off I was. This would help me start to figure out if I am trending in some direction or if I just have a one off variation.

That might be a difficult and somewhat impractical calculator. The reason I say this is that if the models output is already skewed from reality, then you are unsure of where the variance comes from. Is it source water RA, DIpH of malts, error in salt measurement, and so on. Depending on which way that affects the prediction would need to be known to predict the appropriate action. On top of that, without doing a bunch of titrations to model the buffering capacity it’s extremely difficult to target a certain pH. Different grists will behave differently.

I think the cruder small addition, measure, record way is the better way to go. I don’t speak for Martin, though. Maybe he has a different perspective.


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[pfabsits]

1) It is important to note that the pH of a solution is affected by temperature. This affect is not typically compensated for by a pH meter.

2) pH meters with temperature compensation will compensate for changes in the membrane potential (sensing glass) according to the Nernst equation. The Nernst equation is the basis for pH measurement with membrane (glass) electrodes.

This compensation is the reason that a pH meter will show a different reading right after calibration. The displayed reading is the actual pH of the solution at a given temperature (#1). The buffer solutions have known values for pH vs. temperature. For example at 59 ^oF (15 ^oC) the pH of 7.01 buffer is pH 7.04 and not pH 7.01.

According to the Nernst equation (#2) a pH electrode will generate 59.16 mV/pH unit (slope) from pH 7.0 at 25 ^oC. At pH 7.0 the mV is theoretically 0 mV while a pH 6.0 is +59.16 mV. At 15 ^oC the response is approx. 54 mV/pH. ATC compensates for this change in slope.

When a pH reading is taken it is important to note the temperature of the sample because this is the pH of that solution at a given temperature (#1). The same solution can have a different value at a different temperature.

There are other factors that affect pH measurement including conductivity of the water, activity of the ions, condition of the probe (offset/slope), an the list goes on. Overall I would say that if you are within 0.1-0.2 pH of the expected value then you are doing pretty good. To achieve accuracy of 0.01- 0.05 pH is very challenging and would require decent knowledge of pH measurement and best practices.

Basics would be
1) Offset +/- 25 mV
2) Slope 92-105% (54 - 62 mV/pH)
3) Having a clean electrode
4) Having a clean and free flowing junction
5) Using fresh buffers. Ph calibration is only as good as the buffer being used
6) Properly hydrated probe (stored in storage solution for at least 304 hours before use)
7) Use two beakers for each buffer and sample. One beaker to rinse and one to test.
8 Conductivity of solution of at least 100 uS/cm
9) For mash use High Temperature (HT) glass. As temp goes up resistance of the glass goes down. With Ohm's law V =IR the V (voltage) is fixed by Nernst so affecting R (resistance) will also affect I (impedance).  There is an ideal amount of impedance (current) for the meter to measure properly.