Quality pasta needs two ingredients – expert preparation of the dough and correct drying. A controlled drying process is vital to ensure the pasta does not crack or become discoloured. This is why food-processing machine manufacturer Bühler deploys Rotronic humidity probes in its equipment. The company’s machines offer a capacity of up to six tons per hour.
During production, pasta noodles run through numerous temperature and humidity zones in the drying machines. To obtain the necessary quality of pasta, this process must be controlled because if the moisture is withdrawn too quickly, the pasta can crack and render it useless for sale.
Christian Mühlherr, process engineer at Bühler, explains: “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.” Rotronic’s HygroClip2 series humidity probes are used to regulate the drying. Every drier is modular in construction and comprises four to 10 zones; each is equipped with a humidity probe.
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 anymore. Since the pasta dries from outside to inside, its moisture content at the end of the process is higher inside than outside. This results in tensions, which are reduced in the stabilisation phase. After drying, the moisture content in the product lies at about 12%.
“The drying process follows a diagram in which temperature and moisture are plotted,” said Kurt Lieberherr, from Bühler. “These drying charts were obtained empirically. 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, to ensure it does not have a water content of more than 13%.
It’s not only sensor accuracy that is important, because the Bühler driers have lifetimes of up to 30 years and 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. He added: “Our experience with Rotronic has been very good.”
Rotronic Instruments
T: 01293 571000
