Maintaining a controlled diet

Accurate control of moisture and temperature are critical aspects in the production of many types of food and beverage products - as evidenced by recent applications in the sector.

Moisture content is a key consideration in the production of any quality pasta, which needs a carefully controlled drying process to ensure the pasta does not crack or become discoloured.

Food-processing machine manufacturer Bühler, therefore, deploys numerous humidity probes in its equipment to obtain exact measurement results for regulation of the drying climate.

No matter how good the drier is as a whole, if the climate is measured incorrectly, we will have rejects in production

Christian Muhlherr, process engineer at Buhler

“It is extremely important that we use reliable humidity probes in our machines so that we can measure the drying climate as accurately as possible to enable us to regulate the drying process optimally,” explained Christian Mühlherr, process engineer at Bühler.

The company’s engineers use humidity probes from the HygroClip2 series from Rotronic for this. Every drier is modular in construction and comprises four to 10 zones.

After preparation of the dough, the moisture in the product lies at around 30%. The pasta then passes through pre-drying, main drying and finally stabilising phases, in which the noodles give off hardly any moisture.

The drying process follows a diagram in which temperature and moisture are plotted, points out Kurt Lieberherr, who is responsible at Bühler for energetic design of drying machines.

“These drying charts were obtained empirically,” said Lieberherr. “The moisture content of the product at the end of the process depends on many factors, such as shape of the pasta, wall thickness, holding time, and temperature and humidity conditions in the climate zones, as well as on the quantities of air circulated in the product area.”

The final moisture of the pasta can be determined via regulation of the drying process. In this regard, there are framework conditions that must be used.

As Mühlherr explains: “The law states that dry pasta may not have a water content of more than 13%.” If there is more water in the end product, undesirable reactions that have a negative influence on the foodstuff can occur. The case is different with so-called soup foods. In them pasta is filled in bags with other foodstuffs.

“Here it is necessary to consider the critical water activity values of the individual ingredients,” said Mühlherr.

Since the moisture content of the end product plays such a great role, the measurement accuracy of the humidity sensors is critical. The driers from Bühler have lifetimes of up to 30 years or more. The demands on the long-term stability of the probes are correspondingly high.

“No matter how good the drier is as a whole, if the climate is measured incorrectly, we will have rejects in production or problems in process control,” said Lieberherr.

For calibration of the probes, Bühler supplies its customers with a handheld instrument and other accessories. The machine is equipped with blind plugs for control measurements - a further advantage, as Lieberherr explains: “In this way our customers can calibrate the humidity probes themselves. Sensors from other companies often have to be sent in to the manufacturer for this.”

In the US, Diversified Foods, a supplier of ingredients for the food and beverage manufacturers and pre-cooked items fast food chains, has managed to deal with a tricky problem involving one of its products: red beans and rice.

In order to make the product, the various ingredients are mixed in a large kettle and cooked for a number of hours. After cooking, the mixture is placed into plastic containers and delivered to a spiral freezer where the product is frozen prior to shipment to the customer.

The moisture produced as part of the cooking process created a number of problems. Condensation was forming on the ceilings and walls of the kettle room; this created a potential issue with the USDA as condensation is not allowed to come in contact with the product.

“The temperature in the kettle room was approximately 85°F to 90°F with high humidity. We knew if we could drop the temperature to 70°F and lower the humidity many of these problems would go away.” said John Remesnik, plant manager of Diversified Foods.

That’s when Diversified Foods decided to contact Munters to come up with a solution to eliminate the moisture problems: a dehumidification system with cooling to control both temperature and humidity.

“All of the moisture related problems have gone away thanks to Munters,” Remesnik reported. “The temperature and humidity have been lowered to levels that have prevented condensation and fog from forming and the workers are more comfortable due to the changes.”

Temperature control, meanwhile, is a constant concern for chocolate manufacturers, who often face quality and production issues due to variability in the performance of heating systems.

At OP Chocolate’s Dowlais, South Wales factory, a 9kW carbon infra-red heating system from Heraeus Noblelight is helping to ensure consistent chocolate quality while reducing production line down-times. The system is used to pre-heat chocolate moulds prior to filling and replaces a long-established ceramic infra-red system.

The production of moulded chocolate involves depositing liquid chocolate into polycarbonate moulds. However, it is important that the moulds are preheated to a specific temperature before the chocolate is poured. If the moulds are too warm, the chocolate can change its characteristics and detemper. If they are too cold, the poured chocolate will lose shape and possibly crack.

Previously, OP Chocolate had used infra-red, ceramic heaters to preheat the moulds. However, the ceramic system was proving unreliable in operation and the action of changing over the shuttering became increasingly difficult.

The project engineers at OP Chocolate decided to replace the ceramic system with a carbon medium wave system. This proved to be one third the size of the old system. It featured three, 3kW emitters and coud be either manually or automatically controlled.

The infra-red system “provides precisely controllable heating for the moulds and their very fast response ensures that line stoppages are now more easily managed,” said Peter Smith, project manager at Dowlais.