The Wine Analyst

My career has been one of analysis. Yes, I’m one of those analytical types who dissects much of his daily experience into subjects for further investigation. Never could really get the hang of politics, religion or film criticism, but I do take an almost indecent interest in the technical workings of things. That curiosity led me into a career as a Ph.D. analytical chemist – and ultimately, into wine analysis, and making products for that endeavor.

As a 20-year veteran amateur winemaker, I knew there were better ways for home winemakers (and small wineries) to get the basic chemistry information they need for their craft. High on the “annoyance list was sulfite analysis. From desperately slogging my way through color test strips and unreliable Ripper set-ups, both commercial and homemade, I was motivated to find a better way to get that information.

I think it’s fair to say that we succeeded in making a simple, affordable SO2 analysis kit, starting about 5 years ago. Now we have a series of products that get you 5 important parameters: SO2 (free and total), pH, TA, malic acid (for MLF), and residual sugar. We are trying to make a simple ABV test as well, but it doesn’t meet our requirements yet, so no go until it does.

There are some other things though, that you can do with our equipment, so in this blog I’d like to tell you a little about them. These have to do with the pH measurement functions on our SC-200 and SC-300.

Measuring potassium and sodium (and other simple ions):

The latest versions of our firmware (X.1.1 or higher, where X is 2 or 3) for the SC-200 and SC-300 instruments allow you to use the pH capability in a slightly different way. Instead of attaching a pH probe, you can attach one that responds to potassium or to sodium. These so-called ion selective electrodes (ISEs) put out a voltage that is proportional to the sodium or potassium ion concentration, just as the pH probe does for hydrogen ion.

In the potential mode (which we inserted between the pH and TA modes on these instruments) the readout will now be in millivolts. To analyze sodium or potassium, you prepare standards (as well as your samples) in a special buffer that ensures that the readout is not affected by changes in other ion concentrations, or by pH. Then you just put the electrode in and read out the voltage. A simple calculation allows you to relate the voltage response of the standards to the concentration of the sodium or potassium in your sample. It all works very well!
Here is some recent data on potassium (K+ for short). We used a potassium ISE from Van London pHoenix Co.

The slope of this line is in agreement with the manufacturer’s specifications (56 mv/decade concentration, 58.1 theoretical at 20C)

The potassium electrode gives good data in a wine sample, as the table above shows. A red wine sample was run undiluted and at 4 dilutions. The numbers ranges from 44 to 35 mM, but at dilutions of 2-fold and higher, there is less than 3 mM (10%) difference. Note also that three of the dilutions are 37 +/- 1 mM , which equates to 1460 mg/L of potassium, a value not unusual for a California wine.

Measuring Dissolved Oxygen:

You can also measure dissolved oxygen (DO) with the new version of the firmware. A galvanic DO probe is pretty inexpensive, and it attaches to the pH probe position. It puts out a voltage that is proportional to %DO. You calibrate it with water standards: a 0% DO (saturated sodium sulfite that eats up all the oxygen) and a 100% (i.e., air-saturated) DO standard. Then just dip the electrode in the sample; the readout can be converted simply into %DO.
Other electrodes:
there are ion selective electrodes for a large number of substances, including calcium, magnesium, “water hardness”, CO2, nitrate, fluoride, chloride, copper, silver, lead, and “redox potential”, just to name a few.

If you are interested in any of these, let me know. I would be happy to set you up with the source for ISEs, reagents and the protocol – and if there’s enough interest, we could begin to offer these for routine sale!

At Vinmetrica, we are always looking for new ways to improve the utility of our products. If there’s something you’d like to analyze, let us know.