The perfect chocolate challenge: Dr. Michael Kogej explains how to best measure the pH of cocoa butter

Measuring the pH value in viscous media is a difficult task. When processing cocoa butter, it is also necessary to consider the strict hygiene and safety requirements in the food industry. A leading chocolate manufacturer uses Knick's measurement technology for this purpose.

Making chocolate is a complex task, involving many production steps before the finished product reaches the consumer. The first critical step is carried out immediately after the cocoa beans are harvested. In the process of fermentation (a biochemical process), the pungent and bitter taste of the seeds will change to produce the beginning of the desired aroma, which will then be fully utilized during the drying and roasting process.

Due to fermentation, the pH of cocoa beans is relatively acidic at around 5.0 to 5.5. The beans are first shelled and ground, and then the cocoa butter is separated by pressing. The pH value of cocoa butter is an important indicator of product quality, so it must be continuously monitored during the chocolate production process. However, liquid cocoa butter also becomes viscous above the melting temperature of 60°C and tends to become sticky. Therefore, as a medium, it poses a real challenge to the applied measurement technology. Therefore, a leading German chocolate manufacturer used to regularly check the pH of samples in its own quality assurance laboratory. This is a time-consuming and labor-intensive process that the quality assurance department staff are eager to optimize.

The pH measurement value integrated directly in the process is required to meet the strict requirements of the food industry. For example, all components need to be suitable for CIP and SIP, and under no circumstances should foreign objects such as glass shards enter the cocoa butter unknowingly. In this case, a solution is provided by a retractable accessory, where the sensor only comes into contact with the medium for a short time, and then it can be cleaned. During the customer's preliminary trials of this technology, a retractable accessory operated by a push rod was used. However, these accessories proved to be inappropriate because the mechanical system was quickly clogged with cocoa butter and no further measurements were possible.

The company was not deterred and managed to find a solution in Knick's system, which included a combination of Ceramat retractable accessories and Unical's automatic sensor maintenance system. This telescopic joint uses a patented ceramic seal to avoid mechanical blockage caused by the hardening of cocoa butter. The fully automatic, programmable Unical 9000 electro-pneumatic controller activates the retractable accessory to remove the sensor from the process and clean it. To do this, the controller pumps the required cleaning and rinsing solutions from the connected tank into the Ceramat chamber-completely automatically. If necessary, use a suitable buffer solution to calibrate the sensor. All necessary steps are automatically executed by the controller at freely configurable time intervals without any user intervention.

SE555 pH sensor with glass electrode is used for measurement. Since the pH sensor is only in contact with the medium for a short time, it is acceptable to use a glass electrode in this application. Digital Memosens technology is used to transmit data to the evaluation circuit, which actually eliminates measurement errors caused by interference on the signal line (including glass breakage). At the same time, this technology can achieve galvanic isolation between the measuring electrode and the evaluation circuit.

In order to record the measured values, the sensor is connected to the Protos 3400 process analysis system. Profibus PA is used to connect to higher-level process control systems (PCS). For this reason, the flexible Protos system only needs to be equipped with relevant communication modules. The measurement of pH value can be directly triggered by PCS.

The sensor is then immersed in the cocoa butter, the process analysis system transmits the measured values ​​to the PCS, and then the sensor is cleaned and possibly calibrated in the Ceramat retractable accessory. The whole process is fully automatic and very fast. Using this method, the time loss in the quality assurance laboratory measurement process is reduced to a minimum. Through the bus connection of Profibus PA, error messages and alarms can also be directly transmitted to the PCS.

The automatic online measurement of pH in chocolate production is very reliable, and the quality assurance personnel are satisfied with the results. The new system saves a lot of money because it eliminates the need for a large number of manual steps related to laboratory sampling and pH measurement.

Chocolate makers are also pleasantly surprised by the level of accuracy now available, with a deviation of only 0.01 between the online measurement and the pH measurement obtained during the laboratory measurement.

Dr. Michael Kogej with the Knicks

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