Co-extruded, Sweet Products
Sweet creamy fillings in a moulded, crisp extrudate shell
The latest in sophisticated products from direct extrusion are the co-extruded, centre filled products. In these products a soft filling with a pumpable viscosity is metered continuously, using a suitable pump, into an extruded pipe, simultaneously while it is being extruded. A special design co-extrusion die is used for this purpose. The result is an extruded pipe filled with a creamy mass. This pipe can then be moulded into various shapes continuously with the help of special moulding rollers.
Raw-materials: It is important to choose a proper combination of the extrudate raw-materials and the filling mass in these kinds of products to ensure that they combine harmoniously in the final product to give a compatible eating experience to the consumer. Since the handling of the product is completely different from conventional extruded products, matters like elasticity of the extruded pipe and the compactness of the extrudate shell must also be addressed during the designing of the product.
Special care must also be taken to select a filling mass, which is able to withstand high temperature conditions, even though for a very short period, as it passes through the co-extrusion die. The filling mass must also be highly refined to ensure that there is no phase separation after it has been filled into the product. It should also retain its creamy nature and for non-fat based masses, should exhibit nearly zero water activity.
Process: Production of the outer extrudate pipe follows the same procedure as other extruded products.
Pre-extrusion: A single or a blend of multiple raw-materials is moisturised with water or water containing materials to a pre-determined level before being extruded. It is usual for the extrusion mix to contain components like sugar and cocoa powder. The moisturised raw-material is metered into the extruder with the help of screw dosing units.
Filling mass preparation: Depending on the characteristics of the filling mass, it may be necessary to warm it and hold it at a certain temperature till it is pumped into the co-extrusion die system.
Co-extrusion: The extrusion raw-material mix is extruded normally and formed into an expanded pipe. The special co-extrusion die is used to simultaneously combine the filling mass being pumped by a special pump with the extruded pipe in such a manner that the extruded pipe comes out of the die already filled with the mass.
Moulding / Embossing: The filled pipe is continuously fed into the embossing machine, where the embossing rollers with patterns engraved on them press the filled pipe and mould it into the desired shape. The product emerges from the embossing unit in the form of continuous strips of moulded product pieces.
Cooling: For sweet products there is no need to dry the product after moulding, but the strips are passed through a horizontal rotating cooling drum, where ambient air is blown to cool the product and disintegrate the strips into individual product pieces. The fines (parts of the connecting strips holding the product pieces etc.) are sieved out before the product is sent for buffering or packing.
Co-extruded, Savoury Products
The next step in savoury snacks....with savoury fillings!
The initial co-extruded products have been mainly sweet products due to the easy availability of filling masses like chocolate creams and cream masses with a wide variety of flavours like vanilla, strawberry etc. However as technology has advanced and it has been possible to make extrudate outer shells which have shown good characteristics for use in co-extruded products even without the addition of sugar and other similar components, people have seriously started considering savoury co-extruded products as a possible next step to the wide variety of surface flavoured extruded snacks available on the market shelves. Cheese cream and peanut cream snacks are some of the common options in this category.
Process: The production of savoury co-extruded products proceeds along similar lines as the sweet products till the belt conveying stage after the embossing. Hereafter, it is necessary to process the product similarly to other surface coated savoury snacks.
Drying: The co-extruded products in the form of strands are passed through a horizontal rotating drying drum, where the product is dried down to a low moisture level. Upon drying the individual moulded pieces break away from the product strip. Care must be taken to ensure that the drying process does not damage the filling inside the product as these are often quite sensitive to heat.
Flavouring: Depending on the final product design, the dried product pieces have to be passed over a vibratory sievel conveyor to separate out the fines before the product enters a flavouring drum where flavour is applied on it in the form of a combined slurry or separately using a spray of fat and flavour dusting. The flavoured product can now be sent for packing.