Enrobing in the confectionery industry

Quality Street: An example of enrobed confectionery

Through covering the centre with chocolate or compound coatings, the shelf-life of the product may be extended. This is primarily applicable to centres that, if not covered, could be prone to moisture uptake/loss, oxidation, or microbial spoilage. Enrobing has some advantages over moulding (which is another method of getting a chocolate covered centre) such as greater production rates, lower capital costs. Enrobing often allow for greater production rates with lower capital costs than moulding².

Enrobing process

Enrobers are available in different sizes, suitable for large and small scale production and there is a wide variety of different designs to meet all requirements. Belt widths from 125 millimetres to 2600 millimetres are available. Although the basic elements of an enrober have largely remained unchanged over the years, the methods of operation and degree of precision possible have changed significantly. This has been accompanied by a modest increase in throughput. The biggest change in the manufacturing of chocolate enrobed sweets can be credited to the efficiency of the coolers. The basic layout of an enrober is shown in Figure 2.

Processing a real chocolate always requires a tempering unit. Whether fitted with a temperer internally or externally, enrobers have the same basic components (Figure 2). It is important that the centres entering the enrober are maintained at 21-24°C, and that the enrobing chocolate has the desired viscosity and rheological properties. Warmer centres may lead to possible bloom problems due to the residual heat increasing the chocolate temperature of the enrobed sweets. Cold centres can lead to blooming and cracking of the coating shell due to expansion of the centre mass as it warms. Fat bloom develops in different ways. Automatic crystal conversion on the one hand caused by incorrect and/or insufficient tempering; on the other, it may be caused by fat migration from the filling where this fat penetrates the chocolate coat and causes the cocoa butter crystals to rise through the surface. Loss of temper can also be due to heat damage.

The centres are fed on to a feed band and transferred to a wire belt, which passes through the enrober. The coating medium is maintained at a constant temperature and in a controlled condition in an agitated tank; it is then pumped to a flow pan. The flow pan aids the process by creating a continuous curtain of coating and feeding a bottoming device. This leads to the formation of a bed of coating, which floods the mesh band. The centres are passed through this curtain and bed and are covered on all surfaces. After the curtain, excess chocolate is forced off the product by an air blower and a licking roller is used to control the amount of mass left on underside of the sweet. There is normally a vibrator after the blower to remove excess chocolate and to improve the appearance of the sweet. Finally, there should be a detailing rod between and end of the wire belt and the start of the cooler belt. Following the curtain, using an air blower, the excess chocolate is removed and a licking roller controls the amount of mass left on the underside of the sweets³.

The excess mass from the curtain falls through the wire mesh belt into a sump, and is recirculated. Part of the mass is diverted through a de-temperer and is then re-tempered; blending of the freshly tempered and recirculated streams controls the overall level of chocolate in the enrober. Vibrating the centres removes ripples left by the fan, smoothens the coating and removes any surplus chocolate returning it to the tank. The centres are discharged from the enrober on to a cooling conveyor passing over a de-tailer which is a rapidly spinning rod across the end of the wire band. This results in the removal of the tail that forms as the centre leaves the wire band.  

Cooling

After enrobing, the product enters a cooling tunnel to allow the coating to harden. To avoid blooming problems, temperature changes in the tunnel should be gradual, and the relative humidity properly controlled. If the dew point is lower than room temperature, moisture could condense on the product and cause sugar bloom during storage⁴. The chocolate coating and the filling are cooled down to approximately 18°C to ensure trouble-free packaging. A good cooling tunnel should be divided into three zones (Figure 3).

Convection chocolate cooling is a time-dependent but not energy-dependent process. A higher temperature and longer cooling time are more favourable than a lower temperature and shorter cooling time. The recommended cooling times for pure dark chocolate, milk chocolate and milk chocolate with CBE portions are approximately six, eight and 12 minutes respectively. Milk chocolate requires a longer cooling time than dark chocolate due to the higher milk fat content and consequent lower solidification temperatures. Compound coatings may require different cooling profiles i.e. adjusted to suit the setting properties of the vegetable fat used. After cooling, a product which is shiny and resistant to handling should be available for packaging. 

Product attributes

Physico-chemical properties of enrobed products are important for two reasons. Firstly, if the crystallisation or flow properties are incorrect this results in a poor quality product being made, which may have to be sold cheaply as a misshapen product or perhaps has to be reworked. Secondly, sensory attributes are critical to the consumer’s appreciation.

An enrobed product is unlikely to be purchased of if it does not look glossy, or worse still, if the fat has bloomed. One important visual characteristic of enrobed products is gloss. This is determined by the reflected light. If the surface is flat with a lot of small crystals, which happens with correct tempering and cooling, the product appears shiny⁶. Cocoa butter can solidify in different forms of crystals, where only the high melting forms b_v and b_vi are stable. A tempering machine can only effect formation of the crystal form b_v. This crystal form provides good gloss, long shelf life and good mouldability. The b_vi form is a super stable crystal, which forms only after a longer period of storage⁶.

Chocolate or compound flow properties are decisive factors in terms of processing possibilities. The flow properties of a coating are very complicated because the viscosity is not a single value but is dependent on the speed of flow (technically as non-Newtonian fluid). Yield value (YV) is the shear stress required to initiate the flow of a coating. YV is recorded in Pascal (or dynes/cm²). Plastic viscosity is then the force needed to maintain this flow once it is moving, which is recorded in Pascal seconds⁷.

Enrobing of high-quality confectionery items nearly always requires a low-viscosity coating with some reasonable yield value present. The viscosity depends on the level of fat, emulsifier content, temper profile, particle size distribution and temperature. Low viscosity is required for quality lines, giving precise control of coverage to the enrober operators⁸. Without some yield value present, the chocolate would continue to flow down the side of an enrobed piece before setting in the tunnel, resulting in ‘skirts’ or ‘feet’ on the bottom edge of pieces, and decorative markings would be lost (Figure 4).

Generally, bubbles are not a major problem on enrobed items as the coating is fluid enough for them to be displaced or burst by the blower. However, with thicker masses or some more difficult products, bubbles can be problem and action may be needed to minimise them. Each feed pipe to the curtain trough should have its outlet under the chocolate surface to avoid incorporating air. 

Conclusions

Enrobing creates opportunities for manufacturers to create varied, decorative (for example through the use of irregularly shaped inclusions) confections to the ever-demanding consumer. Enrobing also presents some advantages over moulding, by often allowing for greater production rates with lower capital costs. With compound coatings, one can increase speed even more due to quicker setting times.

The basic requirements to enrobe confectionery products have remained unchanged for decades, however the methods used to control their operation and the degree of precision possible have changed significantly, accompanied by a modest increase in throughput.  Products such as wafers, soft centres or cookies can be coated fully or partially with chocolate or compound coatings. Special attention is paid to ensure reproducible and accurate product weights and a uniform bubble-free appearance. Perhaps the biggest change in the manufacture of chocolate enrobed confections has been in the efficiency of the coolers. After cooling, a shiny and uniformly coated product should be available for packaging.  

References

1. Hofberger, R. (2009). Chocolate enrobing fundamentals, The Manufacturing Confectioner, p. 59
2. Gray, M.P. (2009). Moulding, enrobing and cooling chocolate products: In “Industrial chocolate manufacture and use”, ed. S.T. Beckett, Blackwell Publishing Ltd, p. 346-347.
3. Stansell, D. (1993). Sugar and chocolate confectionery: In “Food Industries Manual”, ed. M.D. Ranken and R.C. Kill, Springer, p. 361-397
4. Hofberger, R. and Tanabe, N.A. (2007). Chocolate and Cocoa: In “Handbook of food products and manufacturing”, ed. Y.H. Hui and R.C. Chandan, Wiley-Interscience, p. 675-694
5. Richter, K. (2013). Chocolate process technology, Sollich KG, Germany, p. 4-19.
6. Voltz, M. and Beckett, S.T. (1997). Sensory of chocolate, The Manufacturing Confectioner, p. 49
7. Stauffer, M. (1998). Chocolate behaviour – what influences your selection, The Manufacturing Confectioner, p. 76-77
8. Huggins, C. and Seguine, E. (1997). Tempered chocolate handling – Piping and pumping of tempered mass, The Manufacturing Confectioner, p. 91-92 

About the authors

Dr. Ramana Sundara is a Fellow and Chartered Scientist of the Institute of Food Science and Technology (UK). Currently, he is the Manager of External Research Collaborations at Nestlé Product Technology Centre, York, UK. He has published over 34 scientific papers / presentations and five patents, with an emphasis on fruits, vegetables, chocolate, dairy chemistry and processing technology.

IOGRAP

Ángel Máñez is a Principal Product Technologist at Nestlé Product Technology Centre for confectionery products in York, UK. Ángel joined Nestlé as a post graduate student and first worked on research projects on the chemistry of cocoa fermentation. Subsequent to that he gained experience during two to three years in the area of cocoa processing. For the last 15 years with Nestlé, his main area of expertise has been closely related to chocolate manufacture and usage and in particular chocolate recipe formulation. As part of his present role he provides technical assistance to factories, participates in projects to develop new products and processes and also participates in the commissioning of new lines in factories.

Dr. Josélio Vieira is a Principal Research Scientist at the Nestlé Product Technology Centre for confectionery products in York, UK. Josélio is a Chemist by training and holds a PhD degree in Physical Chemistry from the University of Oxford. After graduating, he worked for 11 years at Dow AgroSciences in the development of crop protection formulations in the Formulation Science & Technology group in Brazil and the UK. He then joined Nestlé at the Product Technology Centre in Beauvais, France, dedicated to ice cream product technology development. After five years in France, Josélio was relocated to York where he now works in the Chocolate Department. His interests include colloidal and formulation sciences. Josélio has co-authored and published a number of research papers and patents on chocolate and ice cream technologies.