Artificial casing
Artificial casings are used in sausage production as a substitute for natural casings . They are made from different, partly edible and partly non-edible materials.
Types of artificial casings
- Collagen-based casings are edible collagen casings of various diameters for the production of cooked sausages , fried sausages and raw sausages . They create a crisp bite in the product. They are permeable to water vapor and smoke.
- Fiber frame casings are highly water-permeable, mostly non-edible casings, which are mainly used for raw sausages such as. B. Salami are used because they have the property of shrinking when smoking , so that the shell does not look unsightly afterwards.
- Plastic casings or plastic casings are casings of plastics and not edible. They are used for thicker, large-caliber scalded sausages, liver sausages and brawn . They have been used increasingly since the 1990s to improve the shelf life of sausages. The plastic protects against germs and avoids weight loss and oxygen access to the sausage.
- Peeled casings are usually plastic casings used for boiled sausages such as Viennese instead of sheep's string (casings). The casing is removed by peeling after smoking. What remains is the so-called own skin , which has formed on the surface from the meat protein after scalding and smoking.
Manufacture of plastic casings
Plastic casings are made by extrusion . A distinction is made between
- uPA shells (non-oriented polymer structure). These are inflated directly at the extrusion nozzle and then wound up.
- oPA shells (oriented polymer structure). A so-called pre-tube is extruded as a preliminary product. This is then calibrated, reheated and only then inflated. Now the inflated hose is pulled. The orientation of the polymer molecules takes place by inflating and pulling the plastic tube. The oriented polymer molecules return to their original shape, as with a shrink tube, when heated to over approx. 50 ° C, and the sausage casing shrinks.
Both forms can be produced with one (mono (layer)) or multiple layers (multilayer or coex) or as a composite structure.
- Only one raw material can be processed in single-layer casings; the casing is homogeneous in its structure. As the material come polyamides or co-polyamides, rare polyester and PVDC used.
- Composite materials made of polyamide and polyethylene with an uneven number of layers (mostly 3-layer) are usually used in multi-layer casings , with polyamide forming the outer layers.
Influence from water
Water is the most important plasticizer for plastic casings. Therefore, the casings are watered before use. The time for soaking depends on the temperature and is longer at low temperatures. However, warm water also triggers accelerated shrinkage, so that in practice temperatures around 25–30 ° C are used. A strong shrinkage starts from 50 ° C.
Barrier properties
Plastic sleeves were introduced in the 1990s to meet the demand for increasingly durable products. Weight loss and the effects of oxidation should be prevented and microbiological stability achieved at the same time.
In the case of plastic covers, this is achieved through the mix of materials: the polyamide provides an oxygen barrier, while polyethylene provides a water vapor barrier.
Manufacturer
Manufacturers of plastic casings in Germany include Kalle GmbH in Wiesbaden , Viskase GmbH (formerly Walsroder Casings GmbH / formerly CaseTec or Wolf-Walsrode) in Bomlitz and Naturin GmbH & Co. KG in Weinheim .