Curing more quickly by the second:Machine controllers in the food industry

Traditional methods for producing meat specialties have barely changed over the centuries. However, these methods proved to be inadequate after the onset of industrialization when meat processing became concentrated in fewer locations. The quantities started to reach industrial proportions, but the old techniques were only slowly replaced by modern processes - proving fatal for the working conditions in enormous abattoirs which went down in history in Paris and Chicago, for example. Relief finally came at the start of the 20   century with the introduction and implementation of health and safety standards. The formation of the FDA in the USA was one of the consequences of this development. Meat processing in particular vividly demonstrates how the arrival of special machines and processes allowed reliable production of high quality products in large quantities. Today’s ongoing development work in the realm of food processing ma-chines focuses on the provision of advanced automation technology. Tak-ing curing as an example, the Rühle Lebensmitteltechnik GmbH high-tech curing center IR 56 demonstrates the extent of progress achieved with modern drive and control components.

Long shelf life, protracted procedure

During the curing process, the water stored in the tissue of a ham is replaced with a salty mixture or brine to create unfavorable con-ditions for micro-organisms. At the same time, the table salt mixture inhibits the activity of en-zymes and the growth of bacteria. This mixture ini-tially contained saltpeter, but this ingredient was replaced by small quanti-ties of nitrite around the beginning of the 20^th century. It also ensures a subtle texture and the combi-nation of nitrite and blood pigment gives the cured ham a reddish color similar to that of raw meat. This process is still widely used today: More than 90% of all types of processed meat and sausages are cured. The oldest process is dry-curing, where hams rubbed with the mixture are stacked and stored in vats for several weeks while being turned regularly. The brine that the hams produce is drained away. With wet curing however, the brine is left in the vat and if necessary, topped up with pre-pared brine to cover all the hams. Alternatively, previously prepared brine can be poured directly over the meat. This process is also followed by a storage period of several weeks during which the hams need to be restacked regularly.

Fig.: 1

Rühle's IR 56 Curing Center

Injecting five tons per hour

The development of a quick or short curing technique using the injection method signaled a technological breakthrough for these processes: A 22 percent brine solution is injected directly into the muscles and blood vessels of the meat using fine needles. After injection, the hams are stacked and stored in a sealed container, then weighed down with weights until the re-quired concentration of salt and red coloring in the meat has been attained. The first automatic curing machine which simplified and accelerated the mechanical injection process was designed by Rühle in 1970. This machine would have little in common with the technology we have today: All proc-esses in the top of the range model of the current series, the IR 56 Curing Center, run fully automatically.

With increasingly fine injection needles and increasingly dynamic drive and control technology, the density of needles in the needle field can be continu-ously increased with every machine model, and the individual movements accelerated to attain a faster and more even distribution of the brine in the tissue: The IR 56 is equipped with precision measurement technology, in-cluding ten actuators and 56 needles that can perform up to 80 punctures per minute. The machine is fitted with a box lifting system and a 350 mm wide bearing surface for ease of operation at maximum capacity: Up to 5000 kg of ham can be cured per hour. All the functions of the center are operated using a touch display connected to a Linux PC. All processing steps are continuously monitored and recorded, from the brine mixing pro-cedure and the injection process to replenishing the circulating brine. The technology directly records any deviations from target values and most of the necessary corrections are made automatically. A self-cleansing assistant shifts all moving parts into a suitable position and cleans the equipment us-ing a high-pressure cleaning system to ensure maximum hygiene.

Key technology control electronics

The high-performance control electronics in the back-ground are predominantly responsible for a wide range of functions on the curing center. The electronics en-able highly dynamic pumping operation as well as an automatic individual needle mode. The SCHLEICHER microLine realtime control is the only control to cover the whole range of different in-jection technologies and sequences.

Fig.: 2

Controller setup for the Rühle Curing Center

The machine controller op-erates in the mode selected by the user on a PC con-nected to the controller via a serial interface.

The microLine, part of the SCHLEICHER RIO system, is the basic module for par-ticularly cost-effective automation solutions: A PLC is integrated into conven-tional bus couplers which can be configured with the relevant language types, structured text, list of instructions, logic and ladder diagram as well as sequen-tial function chart according to IEC 61131. The PLC has full multitasking capa-bility and allows the definition of different cycle times and priorities for a series of subtasks. Up to eight expansion modules can be connected directly to the controller. In addition to standard-24 V I/Os in 8 and 16 blocks, the extensive module system offers channels that can be configured according to require-ments and allows the customized allocation of input or output functions to these channels. Analog channels are available for all types of voltage and current I/O signals. The microLine is ideal for networking using a field bus the processing.power increases correspondingly in line with the number of networked units. Parallel processing means that particularly fast local reaction times can be reached when the bus capacity utilization is low.

Fig.: 3

microLine in the Rühle Curing Center with three digital and one analog expansion module

In addition to digital and analog inputs and outputs, the microLine also allows the connection of functional modules for temperature regulation, positioning tasks and quick counters. The integrated intelligence of these modules also relieves the controller.

Fig.: 4

microLine PLC with I/O Module

Conclusion

At Rühle, the open microLine concept with its flexible expansion capability has already been successfully tried and tested in several machines: It simplified adjustments to meet customer requirements and also accelerated the new de-velopment of other machines. In association with the Linux industrial PC, it re-presents one of the most cost-effective automation solutions in this performance category overall.