Hanna Instruments-99164 Portable pH/Temperature Meter for Yogurt Analysis

The Hanna Instruments-99164 features automatic calibration at one or two points with two sets of buffers. All calibrations and measurements are automatically compensated for temperature variations due to the internal temperature sensor in the FC213D electrode.

The split level LCD displays both pH and temperature readings, along with indicators for reading stability, battery percentage and calibration instructions.

Key features

• Application specific electrode


• Automatic temperature compensation (ATC)


• Stability indicator for accurate data recording

Application importance

Monitoring pH is crucial in producing consistent, quality yogurt. Yogurt is made by the fermentation of milk with live bacterial cultures. Following pasteurisation and compositional adjustment, milk is homogenised for a consistent texture, heated to the desired thickness, and cooled before inoculation. Most yogurt is inoculated with a starter culture consisting of Lactobacillus bulgaricus and Streptococcus thermophiles. Once the live culture is added, the mixture of milk and bacteria is incubated, allowing for fermentation of lactose to lactic acid. As lactic acid is produced, there is a correlating drop in pH. Due to the more acidic mixture, the casein protein in milk coagulates and precipitates out, thickening the milk into a yogurt-like texture.

Yogurt producers cease incubation once a specific pH level is reached. Most producers have a set point between pH 4.0 and 4.6 in which fermentation is stopped by rapid cooling. The amount of lactic acid present at this pH level is ideal for yogurt, giving it the characteristic tartness, aiding in thickening, and acting as a preservative against undesirable strains of bacteria.

By verifying that fermentation continues to a predetermined pH endpoint, yogurt producers can ensure their products remain consistent in terms of flavour, aroma and texture. A deviation from the predetermined pH can lead to a reduced shelf life of yogurt or create a product that is too bitter or tart. Syneresis is the separation of liquid, in this case whey, from the milk solids; this can occur if the fermentation is stopped too early or too late, resulting in yogurt that is respectively too alkaline or too acidic. Consumers expect yogurt to remain texturally consistent, so ensuring fermentation is stopped at the appropriate pH is vital to consumer perception.