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New process trebles sausage skin productivity

Sensors
A team of UK process engineers has developed a technique for manufacturing sausage casings, which is said to treble output.

The process relies on monitoring temperature and humidity with Vaisala sensors, combined with multi-stage feedback control.

The manufacture of collagen sausage skins from animal hide is said to be a good example of sustainable production because it effectively recycles a potential waste product into a valuable commodity that helps to improve the quality and consistency of sausages. However, all sausage casings are delicate and require precise conditions and careful handling during manufacture, storage and distribution, and throughout the subsequent sausage manufacturing process.

Natural casings from the small intestine of meat animals tend to be variable in length, diameter and thickness, so they are not ideal for high-speed sausage manufacturing processes. In contrast, collagen casings offer reliable, consistent features, and are therefore ideal for fast, efficient processes. Also, collagen casings do not need to be stored in chilled conditions and have a longer shelf-life than traditional casings.

Collagen casings are ready to use straight out of the package, horn loading is quick and easy, and there is no requirement for soaking and untangling of bundles. There are no seasonal variations, and sausages manufactured in collagen casings are claimed to offer improved cooking coverage.

Initially, the unnamed sausage skin manufacturer utilised a conveyorised flat sheet collagen dryer, but this incurred a level of friction that could lead to ripping and product wastage. The process was slow and wasteful, so the engineers were challenged to develop a new, less damaging technique for drying and processing the extruded cylindrical collagen cases that are used in sausage manufacture.

Sausage casings have specific physical characteristics and need to be consistent in their properties, so it was vital that the new process minimises friction whilst providing optimal levels of temperature and humidity. If humidity is too high or too low, it can negatively impact the quality of the finished product, so it was important for the equipment to be able to respond to ambient conditions, irrespective of their geographical location.

The new processing solution allows the casings to be inflated with hot, dehumidified process air provided by a silica-based desiccant rotor. New equipment was also developed for transporting the inflated gel using an innovative handling system.

The new system employs three precision sensors. A Vaisala HMT120 humidity transmitter monitors environmental humidity, so that dry air can be recirculated when outside conditions are too humid. In addition, two Vaisala DMT345 dewpoint transmitters monitor process air to ensure that the collagen products are maintained in ideal conditions by a multi-stage feedback control system.

The HMT120 transmitter contains Vaisala’s Humicap technology, a thin-film polymer-based capacitive humidity sensor, which stability and insensitivity to condensation or contamination.

The DMT 345 dewpoint transmitters incorporate the Vaisala Drycap sensor. The sensor is condensation-resistant and is immune to contamination, however, Drycap’s performance is based on its capacitive thin-film polymer sensor and an autocalibration function. The sensor also has a rapid response time and quick recovery after getting wet.

Vaisala’s Juhani Lehto said: “This engineering team routinely utilises Vaisala sensors because their food processing equipment is supplied to customers all over the world, operating in a wide variety of environmental conditions. They, therefore, need sensors that are more than just accurate and reliable in the long-term; they also need to have a low maintenance requirement.”

By minimising friction between the equipment and the casings, the new processing system resulted in less wastage, time-savings and a three-fold increase in productivity.

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