Twin-screw extrusion can offer a modular and flexible method to test and produce new confections. While the use of co-rotating twin-screw extruders for confectionery applications are relatively novel, they do allow for a reduction of floor space usage and manufacturing time necessary for developing and testing new product ideas. Most importantly, it also allows for a shift from a batch to a continuous process. Other advantages include higher hygiene standards, lower energy consumption, and more control over the transformation of raw materials to obtain the desired material properties.


In the following application note we showcase the extrusion of confectionery laces using a Thermo Scientific Process 16 twin-screw extruder and also offer some advice for process development to obtain the desired confection.


Feeding sugary slurries


The first step for every extrusion process, regardless of the application, is to get the feeding right. Feeding sugar slurries into the extruder presents one of the biggest challenges in confectionery extrusion. The slurries can contain between 70 and 85% dry matter and are highly viscous materials. Feeding these materials with a conventional twin-screw gravimetric feeder or with a peristaltic pump is not usually an option. The best way to overcome this challenge is by using a progressing cavity pump. Additionally, the temperature of the slurry plays an important role when dosing. An increase in temperature decreases the viscosity of the material, which in turn facilitates dosing and pumping of the sugary slurry. The best way to characterise the flow behaviour of any melt is using rheometry. The viscosity curves will give an insight into the temperature dependency of the material flow properties and can help to choose the right pump, hose diameter, and temperature settings. Figure 1 shows viscosity’s dependency on the melt temperature. The temperature needs to be kept under 80°C to avoid caramelisation and subsequent hardening of the material.


Extrusion process


The extrusion process of confectionery laces combines multiple unit operations in one single piece of equipment: • •


Feeding of sugar slurry Mixing of the slurry


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Figure 1: Viscosity curves measured at different melt temperatures.


A typical extruder setup for confectionery laces. (Thermo image caption) Coating confectionery laces with food-grade wax using a water bath.


• • • • •


Cooking of starches, melting of fats, caramelising of sugars


Reducing the water content with a degassing port or a vacuum pump to reduce air bubbles


Cooling down the slurry to solidify the melt


Addition of aroma (volatile compounds)


Shaping the product through the die


Another important point to consider is the screw configuration. This must mix and plasticise the starch and retain the melt in the barrel long enough to cool it down to between 50 and 60°C (residence time is key). Typical extrusion speed range from 200 to 600 rpm and temperatures are:


Tbarrel2= 135°C, Tbarrel3= 135°C, Tbarrel4= 135°C, Tbarrel5= 115°C, Tbarrel6= 80 °C, Tbarrel7-8-= 60°C, T die_adapter-= 60°C.


Downstream processing After extrusion cooking, confectionery laces are usually cut to the desired length and coated with a food-grade wax. This prevents the laces from sticking to each other and gives them a glossy shine. Typical methods to wax confectionery laces are spraying them directly after production or using a water bath.


Kennedy’s Confection July 2024 33


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