Accuracy of pH meters

Jim, many home winemakers believe the tart taste of juice or wine is directly related to pH. However, research suggests this is not the case. The tart taste of wine is more related to titratable acid (TA) and only indirectly related to pH. Perhaps this is why tasting the juice or wine seems more important than measuring either TA or pH.

Margalit states in his book "Concepts in Wine Chemistry," page 299 " ............the major factor in acidity taste is the TA, and the pH is just a minor correction."

Here are some other references: Amerine, M.A. et al. - Acids and acid taste; The effect of pH and titratable acid" - Am. J. Enol. Vit. 16 (1965) 29. Nagel, C.W. & McElvain, J.R. - "An analysis of the influence of pH and titratable acid in the scoring of wine" - Am. J. Enol. Vit. 28 (1977) 69. Noble, A.C. et al. - Comparison of sourness of organic anions at equal pH and equal titratable acids" - J. Sensory Studies 1 (1986) 1.

Thanks Lum. I always appreciate your perspective. Am I hearing a recommendation to temper the analytical method and lean more on sensory perceptions? I'd like nothing more than to keep several hundred dollars in my pocket an not buy a pH meter. Yet, I struggle to get a meaningful fix on TA based on color change, especially for reds. I'm left guessing. At my current level my SQ (Sensory Quotient) is not well enough developed to serve me very well. So, I need some aids to give me a sense of what I have. I think a pH meter would help me but I need to be able to trust it's accuracy. Is there a trustworthy meter out there for less than $360 Can.?

Cheers

Hi Jim; I picked up a pH pen from Hoskins Scientific in Vancouver that I am very happy with. It is a model 98128 by Hanna, waterproof, reads to two places of the decimal and cost just over C$100. Stated accuracy is +/- 0.01 with an EMC (?) deviation of +/- 0.02 I don't know if it stays within the stated accuracy of +/- 0.02 or not but isn't that why we calibrate the instrument (?). A pH meter is basically a micro-ammeter. It can be checked/calibrated against a standard. I calibrate my pen at pH 4 and 7. If it then reads the pH 4 buffer accurately (+/- 0.02) I am satisfied that it will be accurate enough to read pH 3.4 which I try to keep my red musts at or below. If it reads the pH 7 buffer accurately (+/- 0.02) I am satisfied that a test for TA at pH 8.2 will be close enough - certainly more accurate than trying to eye-ball a colour change. The Hanna calibration is automatic - just dip it into the buffer and it adjusts itself. There is nothing that I have to physically adjust. I used to have a C$149. Corning pH pen. It was terrible... Did the Labcor rep work on commission ??? LOL !!!

Hope this helps.

Roger

Jim, my approach to winemaking is measure, then taste, then measure, than taste. Of course, the other method of taste, then measure, then taste, then measure works pretty well too. Seriously, I think a reliable hydrometer and pH meter are indispensable for serious winemaking.

I keep a saturated solution of distilled water and potassium bitartrate (buy cream of tarter at grocery store) next to my pH meter. A saturated solution has a pH of 3.56 at room temperature and I use it as a sanity check after I calibrate the meter.

I really can't help you with selecting a pH meter. I am using an old (1973) Orion meter I purchased at a surplus store many years ago. I replace the probe about every two years.

Regards, lum

Rather than rely on the manufactures marketing collateral, why not test the meter against a solution of known strength?

I have Hanna's digital PHEP 5 (80USD). It uses a two point calibration. I first calibrate with their 4.01 / 7.01 solutions, cycle power on the meter, then measure the *known strengths* of the calibration solutions. It consistently reads the calibration solutions +/- 0.05 after calibrating the meter.

I'm not sure if you can then infer that the meter is accurate outside the 4-7 range (e.g. 3-4 for wine, 8.2 for titration), but I don't see why you couldn't. I'm sure someone will jump in if there is a problem with my logic ;-) Regards, Jody

I've been using pHep 5 from Hanna (0.01) accuracy for 2 years now and am pretty happy with it. Can't say if the accuracy is within the bounds, but it's certainly not as bad as you mentioned in the post (about 2 months after last calibration the 4.0 bufer measured at

Pp

Thanks for the comments everyone. The Labcor rep does NOT work for commission and seemed very knowledgable on the subject which is why I let myself get quite confused.

Surely a less expensive pH meter that's calibrated to control solutions should measure pH within an acceptable margin of error (near the listed margin of error). At least that's what reason and [hopefully] sound judgement tell me tonight. I'd much rather spend $80 US than 3 or 4 times that if I can count on accuracy.

Jim

Lum,

I'd love to do a sanity check periodically too. How do you make up a saturated solution of potassium bitartrate (clearly I'm a non-chemist). Does it just mean adding cream of tarter until the solution will hold no more and it just falls to the bottom? Will this solution be good for a pH of 3.56 for some period of time?

Thanks,

Ed

Sounds to me like he was doing a dirty and referring to the drift of an uncelebrated pH meter.

If you do not calibrate it, it can easily be off that much. If you calibrate it, it should be very close to the accuracy they advertise, assuming the electrode is good. I think he was playing loose with his comments.

Ray

I think the Potassium bi tartrate saturated solution will last almost indefinitely - at least until mold or other nasties form in the solution.

Ed, making a saturated solution of potassium bitartrate is easy. Just add enough powder until some is left on the bottom of the container. You know the solution is saturated as long as you can see crystals. My solutions seem to keep for several weeks. However, they do become moldy after a while and the pH is no longer 3.56. lum

Thanks for your help Lum.

Ed

I think Ray hit the nail on the head, my background is calibration and the original premise seems odd. He may have also been talking about non temperature compensated probes but I don't know. I'm not saying he was making it up, I had a Checker and hated it, mine was gawd awful. Some have had good success with them though.

I have the PHEP5 also and love it, but I do calibrate it each use. That is standard practice even with an expensive meter.

I can check 5 points and the accuracy has never been worse than 0.05 from 3.00 to 10.00.

I posted a pH meter FAQ a while back, you can find it with a Google search or I can repost. Regards, Joe

what are the proportions of the measurements that you use to arrive at the

Thanks. Rick

Rick,

Add potassium bitartrate crystals to distilled water until no more crystals will dissolve. The solution is saturated if you can see crystals on the bottom of the container after mixing well.

lum Del Mar, CA

Thanks fellas for the great comments.

I really appreciate the "pH meter FAQ" you posted Joe. That's great. I was looking at the pHep 5 awhile back and thought it would be a good fit for the money. Can you test a large number of samples after careful calibration (as long as the meter is turned on), or do you have to keep returning to the calibration procedure?

Thanks, and cheers,

Jim

Jim, Yes and no. I have one of the first ones and it has an annoying power off feature I can't seem to disable. You get about 5 minutes of use then it powers down.

I recalibrate each time I power it up since mine does not keep it's settings. (I would recalibrate anyway, it's my nature...) I talked to someone at tech support at Hanna about that and he said mine had bad firmware. He told be it's not supposed to do that and I should return it. At that point the meter was over a year old and decided I would just live with it rather than return it. Mine is 2 or 3 years old and still going. The one good thing about the power down setup is it saves on batteries, these are original. I'm sure I use it hundreds of time a year, I have around 15 or 20 lots going plus I do testing for others since I have the equipment.

It's a good meter for the money even with the quirks. It has ATC, the probe is stable and it also indicates sample temp on a small display. It's a toss up as to whether or not its a throw away meter since you can replace the probe too. I'm probably going to replace my meter sooner or later, but it's already paid for itself in peace of mind. I have had a few Pinot Noirs that had really high pH that I never would have caught, they did not taste low in acid to me.

By the way, I would never say spending more on a meter is a bad idea; if I had a commercial operation I would use this meter for spot checks and an expensive one for measurements I documented and made business decisions on. (Measure twice, cut once.. ) :o) I just think paying over $100 for a meter used in a hobby is a bit steep, since the probe will eventually need replaced and that will cost at least $100. This meter is a pretty good bet.

Regards, Joe

Thanks a million Joe for the fullness and helpfulness of your response. The experienced winemakers on this forum, like yourself, generous with help and mentorship, make this NG one of my favourite daily links.

In a year or two (hopefully) I too will become a net contributer rather than mostly a consumer of help and good information.

From the newbies to the more experienced winemakers here:

THREE CHEERS!!

Jim