pH Meters
Hey guys, I'm just after a little advice on pH meters. I've previously tried the narrow-band strips which seemed pretty crappy really.
I'm looking at a bunch of cheap ones from DX for about $20-30 (http://dx.com/s/ph%2bmeters.html?category=421) and wondering if anyone has any experience with these?
I got a bit of a fright from the US folks over on homebrewtalk who often seemed to recommend meters in the $400 range with something in the ballpark of yearly $100 electrode replacements. I'm not trying to discover new frontiers of pH precision as much as getting a roughly accurate figure for mash pH so this would seem to be overkill, no?
Replies to This Discussion
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Permalink Reply by Smiffy on
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I got one like this
http://www.trademe.co.nz/business-farming-industry/industrial/measu...
a couple of years ago. It works fine.
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Permalink Reply by Liam Callaghan on
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As it happens I ordered another one of these on the weekend, arrived today.
Can't beat em for that money!
Great for acidic fermentation if you fancy making chilli hot sauce
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Permalink Reply by Reuben Rowntree on
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I have one too of those cheap ones too. You can just buy a new one of those each year to get you in the ball park. I previously bought a DSE one which was a bit more but that only lasted about a year. Kind of fussy little things really.
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Permalink Reply by mattd2 on
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I notice most of them are only rated to 50°C, anyone know how this affects the ATC/reading?
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Permalink Reply by Damon Colbert on
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This has been discussed before ( http://www.forum.realbeer.co.nz/forum/topics/1500433:Topic:15018 ).
This has some useful information: http://www.jenway.com/faq_pH_Meters.asp
The TLDNR; pH changes with temperature, so if you measure pH at mash temperature that is the actual pH in your mash. This is the pH that mash enzymes are working at. A cooled sample of wort will have a different pH (although probably only a slight difference).
Regarding the effect of use >50C, you would almost certainly take an accuracy hit (potentially of 0.15 pH units or more), if you have calibrated the meter at ambient temperature.
For example
"In the last few years, the development of the electrode has concentrated on bringing the isothermal intersection and the zero point as close together as possible, since the nearer they are to pH 7 the smaller the error in the temperature compensation. The measuring error increases with an increasing temperature difference between the calibration and sample solutions. As a rule the errors can be in the order of 0.1 pH units. The most exact pH value is obtained when the temperature of the calibration and measured solutions are identical"
So the best idea would be to calibrate your meter at ambient (20-25C) and at high temperatures (50-60C). That said, to calibrate at high temperatures you would need to know the actual pH of the buffers at that temperature (most calibration buffers are made for 20-25C). Not easy information to find.
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Reading through some of those post, and as you suggested, to get around the temperature issues could you use this buffer/calibration @ mash temp (seems like it lists the pH at a range of temps on the bottle) ?
http://www.labwarehouse.co.nz/product_info.php?cPath=118&produc...
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Permalink Reply by Gareth Kerr on
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Cheers guys. From reading around a bit, calibrating with a buffer solution like that one at around 65C seems like the best option, but apparently operating the meter at that temp will wear it out faster (how much faster I'm not sure, probably not much of an issue on the cheapos).
If using a buffer that doesn't list pH at different temperatures (as most don't from what I can tell), then you'll need to calibrate/measure at 25C and apply a correction for mash temp, which seems to be a little bit of guesswork. "Studies" have shown that the pH at mash temp (~65C) is about 0.3 units lower than the same sample at room temp (25C), although it seems that this can vary in practice as in the linked article below where he only had a difference of 0.2 or so.
I think I'll probably just calibrate at room temp and get used to shooting for 5.3 – 5.6 at 25C.
Some info here:
http://braukaiser.com/wiki/index.php?title=An_Overview_of_pH#pH_meters
http://braukaiser.com/wiki/index.php?title=PH_Meter_Buying_Guide
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Definitely calibration at mash temp is the best. I'm impressed to see someone does list the calibration temp at high pHs. Just checked the bottles in my lab, the information is listed, so I will have to do that myself now!
I don't think there is a reliable way to apply a correction for mash temp. You certainly could go by those studies, but its going to vary a lot between probes; depending on the internal reference system, the thickness of the glass probe, etc.
Braukaiser does give some great intro information and advice though.
There is still the issue of physical limitations of pH probes in high temperatures. Some manufacturers resources have said that use of an electrode at high temperatures will accelerate the deterioration of the probe. How quickly that happens isn't clear, but may not be a big concern if you're using it only once or twice a month.
Others say gel-filled probes are okay up to 80C, but over 80C Ag/AgCl reference systems are better (and who knows what standard is in the pen pH meters?).
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You're undoubtedly right. You could get an expensive, very accurate pH meter. But it's a bit of work to maintain, and you wouldn't necessarily have the capability to adjust the pH in an accurate manner anyway. Definitely overkill in my opinion.
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Permalink Reply by Nicholas Jones on
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Interesting thread..If you do want something with a little more (potential...) reliability there are these guys http://www.getbluelab.com/shop/Bluelab+pH+Pen.html manufactured in Tauranga, I did some work on one of their truncheons a few years back and they are very high quality.. I also spoke to them about their PH meters 6 mths ago and they said ATC up to 50 deg but their engineer was confident they would be accurate up to 65deg. And NZ made yo'! I kind of prioritised other spend but am now ready for a PH meter so this is the way Im going to go, will report back
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Permalink Reply by Adam Sparks on
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I have a bluelab PH meter. When I first got it I stuck it straight into my mash and killed the probe instantly, after that it wouldn't calibrate, you definitely don't want to go above the recommended ranges. Ive been through a few probes since then, sometimes the gell can get moldy (you need to scrub the tip and wash it well then sanitize then store in water).... Honestly they are really finicky things to maintain, you have to calibrate them every time you use them (and you ned to use fresh solution, so dont buy the little bottles!) and they are just so fragile that at $80 a probe it becomes a real pain in the ass.
However, once you've used it enough with something like the ez water spreadsheet, youll come to realise that the spreadsheet is actually incredibly accurate, and all you need to do is pay attention to that and you'll hit the right numbers (most of the time, sometimes things like special roast and some crystal malts can really lower the ph).
After my experience Id be very surprised if cheaper meters remained accurate when used at high temperatures.... I would LOVE a meter that could be used directly in the mash but they dont seem to be designed like that. By the time you've waited for a sample to cool, the sach rest is already well underway (especially with local two row).... The whole thing is just very fiddly!
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