When it comes to confectionery manufacturing, process controls demand a high level of confidence. This can be achieved with Vaisala's new inline refractometers. These are used at various points in the process and provide continuous measure- ments of total solids or Brix concentrations.

By Dr. Jörg Häseler

A refractometer can be used to measure the concentration of substances dissolved in a liquid. The measuring instrument determines the refractive index of liquid or solid transparent substances and uses the behaviour of light at the transition between a prism with known properties and the substance to be tested.

One of the new refractometers from the measurement technology specialist Vaisala is the K-Patents hygiene refractometer, which is used, for example, by a manufacturer of pralines. The filled chocolates contain cherries and cherry brandy liqueur and are covered with dark chocolate. The manufacturer uses the refracto-meters to control the quality of the liqueur. Alcohol is added to the brandy to achieve the correct liqueur concentration. Unlike other methods, the refractometer is not affected by particles, bubbles, crystals or colours.

Production areas where high alcohol content is worked with must be at least Atex zone 2 certified. The monitoring device must therefore not only be approved for hygiene applications, but also have an Atex classification. In this case, the device had to be intrinsically safe and meet the requirements of Atex zone 0/1. The solution therefore combines 3-A as well as EHEDG and Atex zone 2, 1 or 0.

Refractometers are also used in the processing of cocoa. Its properties, such as taste or water solubility, can be improved by alkalization (Dutching). The type and concentration of the alkali have a considerable influence on the properties of alkalized cocoa powder.

Process refractometers can be used to ensure that the process works within well-defined concentration limits or specifications of the alkaline solution. Such a system can be
installed directly in the alkali preparation tank to measure the concentration in real time. It can also be mounted in a recirculating system or directly in the tank.

Another area of application for refractometers are sugar confectionery. These are made by preparing a diluted mixture of ingredients and then concentrating the sugar content by evaporating the water. The device can be mounted directly in the cooker or in its outlet pipe. In a batch process, a flush-mounted refractometer is installed at the bottom of the vessel. For continuous preparation, the device is installed at the outlet of the cooker.

A flush-mounted refractometer can be installed in a cooker without interfering with the action of scrapers or mixers. The prism is washed with steam or high-pressure water from a wash nozzle that is installed together with the refractometer. Another meter can be mounted on the pre-mixer to ensure the correct feed concentration to the cooker.

The refractometer provides Ethernet and 4 to 20 mA output signals that can be used for real-time process control. If the Brix content deviates from the specified value after boiling, the device sends a signal to the process controller for valve control.