pH/TA Questions – Vinmetrica – Sulfite (SO2), Malic, Alcohol & pH/TA tests for Wine, Beer & Kombucha.

I recently purchased the SC-300 and forgot to screw on the pH storage bottle and probe was left to dry for a couple days. Is my pH probe ruined? If not, what should I do?

Place the electrode back in the storage solution as soon as possible. It may come back to life. Soak the probe in the storage solution (but make sure this solution is clean and clear) for a few days and then try and calibrate it and see what happens. If you do not have fresh storage solution you can soak it in the pH 4.01 reference solution until you are able to get fresh pH electrode storage solution.

My local store is suggesting I use a TA Titrant of 0,1 N or 0,2N (sodium hydroxide) as a replacement of the TA Titrant that came with my Vinmetrica SC-300 kit. Will I get the same results?

The 0.133N NaOH (TA Titrant) that we make is specifically designed to be used with our kit when testing your TA levels. You can use the 0.1N NaOH as a replacement for the TA Titrant however there will need to be adjustments made to your final calculations. You cannot use the simple equation listed at the end of the procedure (TA = 2 * V). You will need to use the longer equation listed above it and replace the 0.133N with the concentration of the NaOH solution that you use. This may blur your endpoint slightly so do take care when performing the titration and make sure to not overshoot the endpoint.

I get a “Good CAL” with 4.0 & 7.0 buffers and get stable readings on wine samples. However, I can never get a stable pH reading on distilled water. Is it possible to test the pH of distilled water?

A better way to test the validity of pH calibration is to measure the pH of a saturated solution of cream of tartar.

Get pure cream of tartar (grocery store stuff is fine, provided it’s pure), or reagent grade potassium hydrogen tartrate, also known as potassium acid tartrate or potassium bitartrate. Call it KHT for short.
Place about 1/8 teaspoon of KHT in 20 mL of distilled water. Mix well for about 30 seconds. You want to be sure the solution is saturated, i.e., everything that can dissolve, has dissolved. There should be some undissolved solid left.
Decant or filter the solution off the solids if possible.
This solution has a standard pH of 3.56 at 25 degrees C (78 degrees F). It should be within 0.02 pH of this value at temperatures from 20 to 30 degrees Celsius. We usually are OK with a value between 3.50 and 3.60. Discard after 24 hours

It is possible to measure the pH of distilled water, but it’s tricky. In principle pure water has a pH of 7.00 at normal temperatures, but as atmospheric CO2 dissolves in the water the pH will drop slightly due to the formation of carbonic acid. In addition, most distilled water from the store, (which by the way is usually de-ionized, rather than distilled), may have very minor amounts of acidity or alkalinity that takes the pH away from 7.00. So even if you degas and boil the water, you may find the pH still not hitting 7.00 and in any case it will start changing immediately on exposure to air.

However, the pH of your distilled water is unimportant for almost anything you want to do with it, because the water has negligible buffering ability. If you were to take 25 mL of it and do a TA titration for example, you will see that less than 1 drop of TA Titrant takes it to way above pH 9, so in essence it has no detectable acidity.

When testing TA, I typically get a lower pH reading after adding 15 ml distilled water to the 5 ml wine sample (i.e. wine is 3.49 pH and wine with 15 ml water is 3.42). This looks like my distilled water may be slightly acidic. Does this skew my final TA results?

The reason that the pH of wine drops on adding distilled water has nothing to do with the water or, up to a point, with the degree of dilution. Rather it has to do with the nature of the pH electrode and how it measures pH. pH is generally considered to be -log[H+], i.e., the negative logarithm, base 10, of the hydrogen ion concentration, but formally it is defined as -log(hydrogen ion activity). Activity a and concentration c are related but not identical: a = g x c where g is the “activity coefficient”. It is this coefficient that is changing as you dilute your wine, becoming closer to 1 with dilution. The pH electrode responds to hydrogen ion activity, rather than its concentration per se.

Also, since wine is a fairly strongly buffered system (primarily by the tartaric acid/tartrate ions, and other acids present) you would have to dilute it over a thousand fold to change the hydrogen ion concentration.

To check your pH calibration, suspend about 1/8 tsp (0.5 g) of pure cream of tartar (aka potassium hydrogen tartrate) in 20 mL of water, stir to dissolve for 30 sec. Some crystals will remain. This saturated solution of cream of tartar has a standard pH at 25C of 3.56. I am good with 3.50 to 3.60. If not, try recalibrating. Make this fresh each day.

Can I conserve SO2 or TA Titrant by placing unused solution back into its respective bottle?

We don’t recommend it because if you cross-contaminate any of the solutions you can cause yourself a major headache in trying to untangle crazy results. But yes, you can do this to save your Titrants but always make sure you are putting it back in the correct bottle.

I want to do a TA test, but the main acid is not Tartaric Acid. Can I report TA as Lactic Acid in beer or malic acid in cider ?

Yes! The SC-200 or SC-300 can be used to test beer, cider or any other beverages. The pH is independent of the beverage or whatever solution it’s measuring.

The TA is also; it’s just a matter of how you calculate and report the final answer. Wine TA is usually reported in terms of tartaric acid, but the Vinmetrica TA titration actually measures acidity as equivalents per liter (eq/L), converting it to g/L of tartaric acid by the equation

TA (g/L tartaric) = 2 * V

as in the manual. The equation assumes the acid is mostly tartaric (true for wine) and incorporates tartaric acid’s equivalent weight** of 75 g/eq into its factor of 2.

For measuring the TA levels in a sour beer you would use the equivalent weight for lactic acid (90 g/eq) since that is the prevalent acid. You can adjust the result of using the above equation to report lactic acid instead of tartaric as follows:

g/L lactic = 90/75 * g/L tartaric.

For TA levels in cider, use the equivalent weight 67 for malic acid since that is the prevalent acid.

**Equivalent weight = molecular weight divided by the number of acid groups. Tartaric and malic acids both have two acid groups, so their equivalent weights are one-half of their molecular weights. Lactic acid has only one acid group, so its equivalent weight and molecular weight are the same.

How much does pH measured with the SC-200 & SC-300 vary with temperature?

After calibrating the unit in both the 4.01 and 7.0 solutions in my house, I go out to test my 52 degree wine tank. Is that okay?

The SC-300 does not have temperature compensation (ATC), however the difference in a pH measurement between 52F and 70F for most solutions is pretty small, less than 0.05 pH units in most cases depending on what the solution is.

If you need to make measurements at 52F, for best accuracy we recommend calibrating with 4 and 7 solutions that are at that temperature. You can do this by storing your pH calibration solutions in the same room as your wine tanks.

You can check calibration at room temperature with a saturated solution of cream of tartar (potassium hydrogen tartrate, KHT for short). Add 1/8 tsp KHT to 20 mL distilled water, stir for 30 sec. pH is 3.55 at 70F. At lower temperatures the saturated KHT is not standardized, but will be between 3.50 and 3.60, so you can confidently check your calibration at 4 and 7 this way.

The ability to test pH with ATC may be an available feature in 2021. Keep an eye our for any announcements in our newsletters.

Additional Information:
There is very little variance of the pH measurement of wine if you are operating within plus or minus 27 degrees F (+/- 15°C) of room temperature, 77° F. The table below will let you know what are typical readings from the pH meter using our reference solutions or other buffers at different temperatures. If you operate the pH meter close to room temperature, 77° F (approximately 25°C) , with the wine sample and the reference solutions also close to room temperature, you should have acceptably accurate measurements with a variance +/- 0.02 pH units.

If you are operating in outdoor conditions or in a cold cellar, the chart below should let you know how much variance is to be expected regarding pH buffers and our pH 4 and 7 reference solutions as well. Since most wines fall within a pH range 3.0 to 4.0, you can roughly approximate the variance in pH to be similar to a pH 3 buffer, a pH 3.49 check solution (50 mM sodium diglycolate), and the pH 4.01 reference solution provided with the SC-200 and SC-300. Even a change in temperature of +/- 27°F from room temperature doesn’t change the pH more than +/- 0.03 pH units with the three solutions mentioned above, so unless you are operating below 50°F or above 104°F, the pH measurements accuracy due to temperature variation is very close to the error of the instrument (+/- 0.02 pH).

PH Variation with Temperature

	Temperature °C	Temperature °F	pH
pH 3 buffer (phthalate)	0	32	2.91
	5	41	2.912
	10	50	2.918
	15	59	2.919
	20	68	2.924
	25	77	2.932
	30	86	2.936
	35	95	2.944
	40	104	2.953
	45	113	2.962
	50	122	2.973
	55	131	2.984
	60	140	2.998

pH 3.49 check solution	5	41	3.47
	10	50	3.47
	15	59	3.48
	20	68	3.48
	25	77	3.49
	30	86	3.50
	35	95	3.51
	40	104	3.53
	50	122	3.56

pH 4.01 reference solution	0	32	4.000
	5	41	3.998
	10	50	3.997
	15	59	3.998
	20	68	4.000
	25	77	4.005
	30	86	4.011
	35	95	4.018
	40	104	4.027
	45	113	4.038
	50	122	4.050
	55	131	4.084
	60	140	4.101

pH 7.00 reference solution	0	32	7.115
	5	41	7.083
	10	50	7.056
	15	59	7.032
	20	68	7.012
	25	77	6.994
	30	86	6.983
	35	95	6.975
	40	104	6.968
	45	113	6.97
	50	122	6.97
	55	131	6.97
	60	140	6.974

What should I do if my pH electrode is difficult to calibrate, or is acting sluggish/erratic?

NOTE: in most cases, calibration problems can be addressed by steps 1-6 below. If your electrode is slow or showing numbers way out of range, try the meter test FIRST (steps 13-16 below). The reconditioning steps (7 – 12) should not normally be needed on an electrode that is less than 6 months old.

1. Be sure your electrode has been stored at least 24 hours in a proper electrode storage solution (Vinmetrica’s product is 3M potassium chloride in 10 mM potassium hydrogen phthalate; other similar products may be used). The entire bottom 1 inch of the electrode needs to have been submerged for at least 24 hours. If this has NOT happened, wait until it has!
2. IMPORTANT! Always stir or gently agitate the solution when using the pH electrode; letting it sit static will cause drift and inaccurate readings!
3. When calibrating your pH electrode, remember that the displayed pH may not be correct until AFTER you press ENTER, and the “Good Cal” message finishes scrolling.
4. If the instrument signals stable pH (i.e., the Cal LED is flashing) but displays “Bad Cal” after pressing ENTER, try putting it flat on the table; when the next stable pH is signaled, press the ENTER button quickly without handling the instrument. Sometimes the instrument may pick up noise from its environment, particularly if you handle it at the last second, while it’s trying to achieve a stable reading.
5. If values appear to drift, leave the electrode in the pH 4.01 reference solution for 30 minutes.
6. If you intend to read pH values in samples that are at a different temperature than ambient, it’s best to have your reference solutions at that temperature also before calibrating.
7. You can restore the pH calibration and bias (DAC setting) values to factory defaults in Test Mode (see Appendix A, Section 13 in your manual). Contact tech support if you have questions beyond this.

Reconditioning and cleaning of pH electrodes

Note: before you try the procedures that follow in steps 8-12, try the simple step of soaking the electrode in your pH 4.01 reference solution for about 1 hour, then try to calibrate. Sometimes this is all that’s needed!
Even in normal use and storage, performance of pH electrodes may show deterioration over time, which typically shows up as noisy, erratic or sluggish electrode readings, and/or difficulty calibrating. Assuming the meter itself is working (see “Meter test” below), then there are two main causes for this:
A. Clogging of the reference junction (most likely).
B. Fouling of the glass membrane (happens occasionally, or after prolonged service).
The following procedures will often provide renewed stability and pH sensitivity. If the electrode cannot be restored by one of these methods, it needs to be replaced.

Unblocking the reference junction:
The reference electrode junction is usually the problem when the electrode can’t calibrate in its expected ranges. This junction is a fine-pored frit that allows electrical contact of a reference electrode with the solution being tested. It can become clogged over time.
8. Soak electrode in hot (NOT boiling!) water, about 60 °C, for 5 – 10 mins. Allow to cool to room temperature then place in pH 4 reference solution for 5 minutes. Try to recalibrate. If this does not work, try the next step.
9. Place electrode in electrode storage solution (from Vinmetrica, or 3M KCl with optionally added 0.01M potassium acid phthalate, KHP) at 60 °C and allow electrode and solution to cool to room temperature, then place in pH 4 reference solution for 5 minutes. Try to recalibrate. If this does not work, try the next step.
10. Soak in 0.1M HCl (note: this can be made by diluting 1 mL of the SO2 Acid Solution with 20 mL DI water) or HNO3 for 1 hour. Rinse with DI water, then place in pH 4 reference solution for 5 minutes. Try to recalibrate. If this does not work, try the next step.
11. Soak in 1:10 dilution of bleach in a 0.1 – 0.05 % solution of liquid detergent in hot water with vigorous stirring for 15 mins. Rinse with DI water, then place in pH 4 reference solution for 5 minutes. Try to recalibrate.

Cleaning the pH electrode’s glass membrane:
The glass bulb is a thin membrane of a special kind of glass that actually does the job of responding to the pH of the solution. It can sometimes become dirty and poorly responsive.
12. Immerse electrode tip in 0.1M HCl (see above for how to make) for about 15 secs., rinse with distilled water, then immerse in 0.1M NaOH (you can use a little of your TA Titrant for this) for another 15 sec. Cycle the electrode through these solutions several times (rinsing with DI water in between), then rinse and check for performance in pH buffer 4.00 and 7.00.

Meter test

You want to be sure that the instrument is responding correctly. A quick test is to simply short out the electrode connector:
13. Put the instrument in pH mode.
14. Remove the electrode to expose the BNC connector at the back of the instrument. Short out the terminals on the connector, using a paper clip or similar metal piece to touch the center pin of the connector to its outer metal sheath.
15. With the input shorted out, the reading should be pH 7.00 +/- 0.5. If out of this range, the meter is probably bad. Contact us.
16. Bear in mind that this test is not 100% fool-proof (the instrument might still have trouble reading pH values different from 7.00), but generally if this test passes, it is much more likely to be an electrode problem.

pH test with cream of tartar

A quick way to check your calibration and pH accuracy is to measure the pH of a saturated solution of cream of tartar which has a pH of 3.56 at 25 degrees celsius:
a. Get pure cream of tartar (grocery store stuff is fine, provided it’s pure), or even better is reagent grade potassium hydrogen tartrate, also known as potassium acid tartrate or potassium bitartrate. Call it KHT for short.
b. Place about 1/4 teaspoon of KHT in 20 mL of distilled water. Mix well for about 30 seconds. You want to be sure the solution is saturated, i.e., everything that can dissolve, has dissolved. There should be some undissolved solid left.
c. Decant or filter the solution off the solids.
d. This solution has a standard pH of 3.56 at 25 degrees C (78 degrees F). It should be within 0.02 pH of this value at temperatures from 20 to 30 degrees Celsius. Discard after 24 hours.

PH Variation with Temperature