Yogurt has gained popularity as a go-to food choice. Not only is it delicious and versatile, but yogurt also boasts a wealth of health benefits that support overall well-being. And as busy professionals try to balance work, family life and other responsibilities, it has become a convenient staple of breaktfasts and lunches everywhere.

Among the health benefits of yogurt: improved digestion, enhanced immune function and better nutrient absorption. Key to these health benefits are yogurt's probiotic cultures — live microorganisms that flourish in the intestinal microbiome. Keeping these cultures alive from factory to first bite means maintaining the correct pH in the yogurt container.

The yogurt fermentation process lowers the pH of milk from 6.7 to 4.6 or lower, creating an acidic environment that inhibits harmful bacteria while promoting the growth of beneficial probiotics. The yogurt-making process starts with homogenization and pasteurization, followed by cooling to the ideal incubation temperature for adding the starter culture. Fermentation begins with live bacterial strains that lower the pH through lactic acid production. This pH reduction is carefully monitored until it reaches the manufacturer’s target of 4.6 pH units or below. Next, the mixture is partially cooled to below 20° C, and any desired fruit or flavorings are added. Finally, the yogurt is moved to cold storage to halt further acid development, resulting in a tasty final product ready for enjoyment.

The probiotic benefits, flavor and shelf stability of yogurt samples are all influenced by pH measurements taken during the manufacturing and quality control processes.

Measurement of pH in yogurt

InLab Solids Pro-ISM sensor from Mettler Toledo.

The pH measurement is done using a pH meter and an electrode. However, measuring the pH of yogurt using conventional pH sensors is quite challenging due to various factors. High protein sample content can lead to sensor junction damage due to clogging, preventing the reference electrolyte from further mixing with the sample. Whereas the high-fat sample content results in sensor fouling due to deposition on the glass membrane. The semi-solid consistency of yogurt necessitates prior sample preparation, typically involving dilution with water, which carries a high risk of errors, whereas direct insertion of a sensor into the yogurt sample may lead to sensor damage.

Measurement best practices

1. The pH range for the sensor is 1 pH to 11 pH units, so it should not be exposed to harsh acidic solutions (below pH 1.00) or alkaline solutions (above pH 11.00).

2. To prevent contamination and ensure a quick sensor response, clean the electrode surface after each pH measurement.

3. After taking a sample measurement, thoroughly clean the electrode surface with a mild soapy solution and rinse it with de-ionized water to remove any residues.

4. Always use fresh buffers and follow the correct sequence for their use. Be sure to check their expiry dates.

5. It is important to avoid storing the electrode either dry or in distilled water, as this can damage the pH-sensitive glass membrane and reduce the electrode's lifespan.

Mettler Toledo provides a step-by-step guide for pH analysis of yogurt samples. You can also find the right pH tool for these applications.