Overview
Ageing, freezer and filler in ice cream production
Final processing and dosing of cream mixtures
The final processes in ice cream production are ageing, freezing and filling. The cream mixture must be aged for at least 4 hours at a temperature of between 2 and 5°C, with continuous gentle agitation. Ageing allows time for the stabiliser to take effect and the fat to crystallise. The continuous freezer has two functions. It has to whip a controlled amount of air into the mix, and to freeze the water content in the mix, forming a large number of small ice crystals. The mix is pumped into a cylinder refrigerated by an ammonia jacket. The freezing process is very rapid; this is very important for the formation of small ice crystals. The layer of frozen mix on the cylinder wall is continuously scraped off by a rotating, knife-equipped mutator inside the cylinder. From the ageing tanks the mix is passed to the continuous freezer, where air is whipped in while it is frozen to between –3°C and –6°C depending on the ice cream product. The ice cream leaving the continuous freezer has a texture similar to soft ice, and some 40% of the water content is frozen.
This consistency allows the mixture to be pumped to the next stage in the process, which is either packing, extrusion or moulding. Ice cream is packed in cups, cones and containers (1 to 6 litres) in a rotary or in-line filling machine. These can be filled along with various flavours, and the products may be decorated with nuts, fruits and chocolate. The packs are lidded before leaving the machine, after which they are passed through a hardening tunnel where final freezing (down to –20°C) takes place.
The amount of overrun in the frozen ice cream is one important quality parameter. In combination with pressure transmitters the Coriolis mass flowmeter OPTIMASS 6400 can measure the overrun in the frozen ice without the need of taking separate samples. The high accuracy BATCHFLUX flowmeters, designed for volumetric filling systems, can precisely dose the small amount of sauces which are added on to the top of the finished ice cream.