It’s a great time to be a dairy lover. Supermarkets are stocking shelves with more products than ever before due to increased consumer demand. Yoghurt has surged in popularity in recent years with the introduction of Greek yoghurt, whipped yoghurt, and yoghurts containing probiotics. This explosion in popularity has caused yoghurt manufacturers to re-evaluate their production processes in an effort to ensure customer needs are met.
Monitoring pH is crucial in producing consistent, quality yoghurt. Yoghurt is made by the fermentation of milk with live bacterial cultures. Most yoghurts are inoculated with a starter culture consisting of Lactobacillus bulgaricus and Streptococcus thermophilus. Once the live culture is added, the mixture of milk and bacteria is incubated, allowing for fermentation of lactose to lactic acid. The pH of the mixture drops and becomes more acidic due to the lactic acid production; it is this reduction in pH causes the casein protein in milk to coagulate and precipitate, resulting in a yogurt-like texture.
Yoghurt producers cease incubation once a specific pH level is reached. Most producers have a desired point between pH 4.0 and 4.6 in which fermentation is stopped by rapid cooling. Within this range of pH there is an ideal amount of lactic acid present for yoghurt, 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, yoghurt 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 yoghurt or create a product that is too bitter or tart. Syneresis can also occur if fermentation is stopped too early or too late, resulting in yoghurt that is respectively too alkaline or too acidic. Syneresis is the separation of liquid, in this case whey, from the milk solids. Consumers expect yoghurt remain texturally consistent, so ensuring fermentation is stopped at the appropriate pH is vital to consumer perception.
Yoghurt can provide a number of challenges for the person that needs to measure pH. Yoghurt is a semi-solid to slurry that has a very high solids content. This type of sample will coat the sensitive glass membrane surface and/or clog the reference junction.
This is why Hanna Instruments created a pH meter designed specifically for measuring pH in yoghurt. The HI98164 meter is supplied with the FC213 probe: from a conic tip shape for easy penetration to an open junction that resists clogging; the FC2133 is an ideal general-purpose pH electrode for yoghurt products. The FC2133 connects to the HI98164 with a quick-connect, waterproof DIN connector, allowing for a secure, non-threaded attachment.
Besides being supplied with a unique pH electrode made for yoghurt, the HI98164 has the Hanna’s unique CAL Check™ feature that alerts the user to potential problems during the calibration process. This is a very important for the food processor since it is likely that the probe will be coated with the solids found in the food product being measured. This coating can easily lead to errors in pH measurement. By comparing previous calibration data to the current calibration, the meter will inform the user, with display prompts, when the probe needs to be cleaned, replaced, or if the pH buffer might be contaminated. After calibration, the overall probe condition is displayed on screen as a percentage from 0 to 100% in increments of 10%. The probe condition is affected by both the offset and slope characteristics of the pH electrode, both of which can be found in the GLP data.
Pressing the “AutoHold” virtual key in measurement mode, the meter will freeze and automatically log a stable reading. An “out of calibration range” warning can be enabled that will alert the user when a reading is not within the bracket of calibrated pH values.
The log-on-demand mode allows the user to record and save up to 200 samples. The logged data, along with the associated GLP data, can then be recalled or transferred to a PC with Hanna’s HI920015 micro USB cable and HI92000 software for traceability in record keeping for specific product batches. GLP data includes date, time, calibration buffers, offset, and slope, and is directly accessible by pressing the dedicated GLP key.
A contextual help menu based on the screen that is currently being viewed can be accessed at any time by the press of a dedicated button.
The high contrast, graphic LCD screen is easy to view outdoors in bright sunlight as well as in low-lit areas with the backlight. A combination of dedicated and virtual keys allows for easy, intuitive meter operation in a choice of languages.
The compact, durable HI720190 carry case is thermoformed to hold all necessary components for taking a field measurement, including the meter and electrode, beakers, buffer solutions and cleaning solutions.
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