The co-extrusion technology is mainly used for production of large scale sausage production. It is a fully automatic system, and the output per hour is high. The unit extrudes a continuous flow of meat emulsion, and on this a thin layer of casing gel is extruded. The casing is created as the sausage is produced.
The sausage, plus coextruded casing material, enters a bath of brine (typically NaCl or CaCl2) in order to make collagen to crosslink into a casing. After cutting the sausages in the correct length they are pre-dried at typically 80-110 degrees celcius. Smoke flavouring is applied at a temperature of 30-40 degrees celcius, and dried once. Then they are packed and typically pasteurized.
The liquid smoke used is typically ph adjusted to pH 5-6 and water-soluble. The carbonylic components in the liquid smoke make sure to cross link the collagen and create browning. Other flavour components in the smoke flavouring make sure to add the smoky flavour to the product.