Measuring pH

 

Definition

The pH is a logarithmic scale for hydrogen ions (H+) concentration in a liquid solution: pH = -log[H+]. It is a measure of a solution's Acidity (low pH) or alkalinity (high pH). Pure water has a pH of ~7, and acidic wine has a pH of 3 to 4. A pH of 4 indicates 0.0001 mol/L of ions, while a pH of 4 indicates ten times more ions, 0.001 mol/L.

Relevance

From the winemaker's perspective, pH may be the most critical chemical parameter in premium wine production as it is known to have significant effects on the following:

  • Biological stability: The lower the pH, the less chance for bacterial growth, and the higher the pH, the greater opportunity for bacterial spoilage

  • Color: At higher pH values, the color tends to be in the blue range and highly unstable with the precipitation of pigments. At pH 3.0, approximately 40% of free anthocyanins are in ionized colored form, while at pH 4.0, only 11% are in the colored state.

  • Oxidation rate: Higher pH wines tend to be poised toward oxidation.

  • Protein stability: Concerning protein, lower pH tends to foster more rapid precipitation of unstable fractions.

  • Bitartrate stability: Potassium ions play a critical part in the distribution of tartaric acid into its various forms of bitartrate and tartrate.

  • Overall palatability: High pH wines generally can be described as flat, while overly acidic wines are too "tart."

  • Sulfur interactions: At lower pH values, you need far less sulfur to protect wine, while at higher pH readings, more SO2 is necessary to increase the molecular fraction with anti-microbial activity.

We adapted these bullet points from information on Enartis's website (www.enartis.com ). The pH of must or wine can be adjusted downward to increase its stability by adding tartaric acid. Alternatively, it can be adjusted upwards through the addition of potassium bicarbonate.

Measurement

Until 2017 we used a portable pH meter to measure the pH of juice, must, or wine, and we used a variety of benchtop pH meters to track changes in pH during a titration. Since 2017 we have used OenoFoss, which constantly eliminated the need to calibrate the pH meters with reference solutions.

Handheld measurement

For handheld measurements, we used a HANA 92128. It is essential to recalibrate the instrument if it has not been used for more than 24 hours. To calibrate, follow either of these procedures:

  • Single point calibration with buffer 4.01: When the meter is on, press and hold the start button until REC appears on the screen and place the meter into the 4.01 buffer. Wait until the message OK appears. Now the meter is ready for measurement.

  • Two-point calibration: Place the meter into a 7.01 buffer and calibrate as in a single point. After the first calibration point has been accepted, the "Ph 4.01 USE" message appears, and you have 12 seconds to place the meter into a 4.01 buffer. When the second point is accepted, the display shows the value with the "OK 2" message. Now the meter is ready for measurement

For calibration video, see http://www.youtube.com/watch?v=cPbBZqgT4KQ

Benchtop measurement

We used a Beckman-Coulter Series 500 benchtop pH meter or a Hana Edge meter for benchtop measurement. Again, if the instrument has not been used for a few days, it must be recalibrated. (https://www.beckmancoulter.com/wsrportal/wsr/research-and-discovery/products-and-services/electrochemistry/500-series-benchtop-meters/index.htm?i=A58748)

Since 2017 we have used OenoFoss to measure pH.


 

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Last updated: May 16, 2023