Measuring pH

 

Definition

The pH is a logarithmic scale for the concentration of hydrogen ions (H+) in a liquid solution: pH = -log[H+]. It is a measure of acidity (low pH) or alkalinity (high pH) of a solution. Pure water has a pH of ~7, Wine which is acidic has a pH in the range of 3 to 4. A pH of 4 indicates there are 0.0001 mol/L of ions, a pH of 4 indicates there are 10 times more ions, 0.001 mol/L.

 

Relevance

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

  • Biological stability: The lower the pH, the less chance for bacterial growth, and the higher the pH, a greater chance for bacterial spoilage
  • Color: At higher pH values, color tends to be in the blue range and highly unstable with 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 form.
  • Oxidation rate: Higher pH wines tend to be poised toward oxidation. 
  • Protein stability: With respect to 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 needed to increase the molecular fraction that has anti-microbial activity.

These bullets were adapted from information on Enartis’s website (www.enartis.com ). The pH of must or wine can be adjusted downward to increase its stability through the addition of tartaric acid

 

Measurement

We use a portable pH meter to measure the pH of juice, must or wine, and we use a benchtop pH meter to track changes in pH during a titration.

Handheld measurement
For handheld measurements we use a HANA 92128. It is important to recalibrate the instrument if it has not been used for a few days. 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 meter into 4.01 buffer. Wait until the message OK appears. Now the meter is ready for measurement.
  • Two point calibration: First place the meter into a 7.01 buffer and calibrate as in 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 more info, check the Hanna website

For calibration video, see 

Benchtop measurement

For benchtop measurement we use is a Beckman-Coulter Series 500 benchtop pH meter. Again, if the instrument has not been used for a few days, it is advisable to recalibrate it. The procedure is described in the manual. (click here)

 

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Last updated: December 27, 2014