PH woes

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Belter

PH woes

Post by Belter » Sun Jun 23, 2013 12:46 pm

Today I tested my HI-98127 PH meter.

I calibrated in buffer solutions 4 & 7 at 20oC and the meter made this really easy.

I tested my mash but it was a little hot. Came out at 5.4 out of the tap and 5.5 put of the top of the mash tun. I figured I'd do both to make sure.

This didn't seem a problem at all. It has ATC as a feature but I didn't want to trust that as I've read that ATC is a bit of a joke.

I then was messing around and tested the PH of distilled water. It started at 7. The instability symbol showed up and it gradually dropped to 6.2. I then tested my tap water 8.8.

In between I rinsed it every time with the solution I was about to test next and prior to that rinsed with distilled water.

I wasn't happy with the reading so I put the meter in the buffer to see if after calibration and use it had varied. Without calibrating again I got 6.9 and 3.9. Then the Same issue. The meter was unstable for over ao nite while I creeped 0.1 at a time until 6.2 distilled water and 8.8 tap water.

I've read that when distilled water is exposed to air it gains carbon and this can affect PH. I was probably messing around for an hour or two. Can buffer solutions vary when exposed to oxygen? Can distilled water vary that much over a couple hours?

If my tap was 8.8 I'd have a bit of a problem wouldn't I?

When the mash had cooled to 20 degrees I got 5.5 tap (same sample) and 5.6 top (same sample).

The readings are too close for me for the meter to be reading incorrectly but I don't understand why in water (distilled and tap) it seems to fluctuate in different directions and so slowly.

I have very soft water and use that to calibrate my refractometer because I did it in both solutions and the result was still 0.

Murphys say my water is PH6.2 which is what I got for the distilled tap was 8.8.

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mabrungard
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Re: PH woes

Post by mabrungard » Sun Jun 23, 2013 2:55 pm

If the wort was just a little hot, say 35C instead of 20C, then the ATC can help. But it does not help when the wort is at mash temperature. There are two mechanisms at work. The ATC corrects for the temperature dependent response of the probe. However, there is another temperature dependent variation in pH due to the dissociation activity of the wort and ATC does not correct for that. That is why its important to cool the wort down most or all of the way when testing pH.

Buffers are formulated to resist the kind of pH variation that was observed with distilled and tap water over time. I'm not surprised to hear of a variation when the meter was left in the solutions for hours. Considering that we are typically only using a pH meter for about an hour on a brew day, I'm less concerned with the calibration changes that occur over hours. I recommend calibrating and using a meter straight away on your brew day. With proper cooling of the wort prior to pH measurement, the result should be fairly reliable.

If your water is fairly soft, then it probably doesn't have much alkalinity either. The Murphy's result might be reasonable in that case. But a low pH like that is corrosive to the water company's piping and I wouldn't be surprised if they adjust pH to protect their system. Are you sure that the water hasn't changed?
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Belter

Re: PH woes

Post by Belter » Sun Jun 23, 2013 3:04 pm

Thanks for your response Martin. The PH meter wasn't left in solution for hours. The buffers were left on the shelf in glass beakers for two hours. I only used the meter temporarily.

I wasn't dissatisfied with the readings I got for Wort as after it had cooled they were within range. Bru'N'water suggested 5.3 but it came out at 5.5. I wasn't that worried about that as its my firs proper play with a meter.

The thing I was worried about was that my tap water came out at 8.8. Surely that's impossible? And distilled water 6.2. I was expecting somewhere around 7 for both.

Belter

Re: PH woes

Post by Belter » Sun Jun 23, 2013 5:44 pm

I think Dunc has a Hanna meter? Are you about mate?

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Re: PH woes

Post by Befuddler » Sun Jun 23, 2013 5:53 pm

Belter wrote:tap water came out at 8.8. Surely that's impossible?
Definitely not impossible. According to my latest water report, it varied between 7.5 and 10 over a year! The high reading was an unexplained failure, which gradually dropped back to normal levels, but I believe regulations are between 6.5 and 9.5.
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mabrungard
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Re: PH woes

Post by mabrungard » Sun Jun 23, 2013 6:04 pm

Water pH is rarely at 7. Even distilled water will fall well below 7 when exposed to CO2 in the atmosphere. The pH of typical drinking water with moderate to high alkalinity is typically well above 7. As mentioned above, there are typically regulations regarding the pH of tap water. In the US, those pH regulations are secondary standards that are recommendations and not legal requirements. Its in the water utility's interest to keep their water pH within those bounds to avoid corroding their pipes or scaling them up.

I have found that a meter typically needs to be turned on for at least 15 minutes to get a unit to stabilize better. Maybe there is some sort of warming up that either the meter or probe is undergoing? Its not like there is much current, so I don't understand what's going on with that phenomena. But it has proven to be valid for the meters I've owned.
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Re: PH woes

Post by bigrichlock » Sun Jun 23, 2013 6:24 pm

I'm up in Plymouth and the water report from Southwest report states a minimum of 7.4 and a max of 9.2 and an average of 8.4, so a fluctuation is to be expected during the course of the year.

The water is extremely soft so has a very low RA so the acidification/alkalinity is easily changed (little buffering ability) with the use of dark grains or salts etc.

I have the same pH meter and it works well, would be worth giving it another try.

Rich

Belter

Re: PH woes

Post by Belter » Sun Jun 23, 2013 6:32 pm

I've been testing for the last half hour to try and work it out. I have a sample from the tap that measures 8.3. Another sample from the same tap 9

Belter

Re: PH woes

Post by Belter » Sun Jun 23, 2013 6:33 pm

How long does it take for you to get an accurate reading Rich?

Belter

Re: PH woes

Post by Belter » Sun Jun 23, 2013 6:41 pm

It does seem to depend on temp. Perhaps I misunderstand the ATC function. I get 8.2 at 20.3 degree and 8.6 at 19.6. These are two different samples at two different temperatures from the same tap

Do I have to make sure my samples are bang on 20oC?

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Re: PH woes

Post by bigrichlock » Sun Jun 23, 2013 6:45 pm

Once the meter is calibrated and i place it in a wort sample or in tap water the reading stabalises in a couple of mins with the icon thing disappearing.

Rich

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Re: PH woes

Post by bigrichlock » Sun Jun 23, 2013 6:48 pm

The ATC function should work well over the temp differences you are talking about - i would think, but for calibrations the temps of the cal solutions need to be bang on 20deg is my understanding.

Rich

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Re: PH woes

Post by orlando » Sun Jun 23, 2013 7:05 pm

I keep my calibration solutions in the brewfridge, typically 20, but will look to calibrate and measure at the same temp of the solution whatever it may be. I don't have your meter though so can't help there.
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Belter

Re: PH woes

Post by Belter » Sun Jun 23, 2013 7:10 pm

I think I've worked it out. If I test the PH the moment the water comes out of the tap I get 8.8/8.9 every time without fail. If the water is left it can go down as far as 7.8. I take it this is as chlorine evaporates and carbon leaves the water? Therefore my PH is 8.8?

If this is correct how would that affect my mash PH being as the water will have been heated etc etc.
I need a starting PH for bru'n'water spreadsheet...
Last edited by Belter on Sun Jun 23, 2013 8:11 pm, edited 1 time in total.

Belter

Re: PH woes

Post by Belter » Sun Jun 23, 2013 7:12 pm

orlando wrote:I keep my calibration solutions in the brewfridge, typically 20, but will look to calibrate and measure at the same temp of the solution whatever it may be. I don't have your meter though so can't help there.
I'm in the process of converting a mini fridge into a starter/PH solution temp controlled environment so hopefully that should be sorted soon

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