Determining pH During Cheesemaking

If measuring the pH of cheese with an electrode constructed of a spherical bulb and ceramic reference junction, a homogenized slurry of cheese and deionized water must be prepared. A slurry is necessary because the flow rate of electrolyte into a solid or semisolid cheese alone is too slow to enable a direct measurement. An electrode utilizing a conical tip shape in combination with an open reference junction allows for direct measurements of cheese samples, thus saving on preparation time and eliminating a potential source of error. Conversely, for other dairy products such as milk or cream, the spherical tip may be more suitable due to its wider area of contact that permits a faster stabilization time. Ultimately, selection of the tip should be based on the nature of the sample matrix.

Temperatures

A wide temperature range is covered in the cheesemaking process; pH measurements may be taken in refrigerated conditions or conditions as hot as 85 degrees Celsius, which is seen in the production of ricotta. This presents a measurement challenge since hydrogen ion activity, and therefore pH, changes based on temperature. Temperature compensation allows measurements at high and low temperatures by comparing the measured pH to a reference temperature. Automatic temperature compensation is available on most pH meters so users do not have to consider their temperatures during measurement.

Temperature also changes the behavior of the pH sensing glass. As temperature increases, the impedance of the glass decreases, and vice versa. This relation means that while a reading may stabilize more quickly at higher temperatures, the glass degrades at a faster rate. Conversely, readings may take a long time to stabilize under low temperatures due to the higher impedance. Manufacturers minimize these measurement difficulties by producing different glass formulations specifically designed for high or low temperatures. In short, if measurements must occur in both hot and cold samples it may be desirable to have an electrode dedicated for each of these extremes. However, if measurements are normally taken under standard conditions and only rarely under extreme conditions, it may be best to perform measurements with a general-purpose electrode.

Details for when and where to monitor pH can change depending on specific product, but in all cases, proper electrode care and design selection is key for reliability of measurement. When implemented properly, pH measurements can ensure safe, consistent, and quality products.

Masulli is application engineer at HANNA instruments. Reach him at [email protected].