Whether it is consumed on its own as a dark, milk or white chocolate bar, or if it is used for enrobing baked products like biscuits, cakes and cereal bars, chocolate is a widely appreciated ingredient. Chocolate creates a unique eating experience for the consumer with its resistance to the bite, its mouthfeel and how it melts on the tongue and releases flavors.
By Gael Delamare, scientist, ingredient research, Production and Processing Research Department, Campden BRI
The flow properties of chocolate are important for several reasons. For example, when chocolate is used to enrobe biscuits, cakes or cereal bars, the viscosity of the enrobing chocolate needs to be adjusted. If the viscosity is too low, the chocolate will flow too easily around the product that needs to be coated and an insufficient amount of chocolate will remain on the product. Conversely, if the viscosity is too high, the chocolate will flow too slowly around the surface of the enrobed product and chocolate “feet” can appear at the bottom of the product. It may also be more difficult to remove air bubbles from molded tablets when the chocolate is too viscous.
The flow behavior of the chocolate will also have an impact on how it moves in pipes and stirring tanks. It’s important to remember that the flow behavior of chocolate is complex as it is a non-Newtonian fluid and its viscosity will vary depending on the shear rate, or rate of movement. For example, the shear rate when enrobing chocolate runs down the side of an enrobed product is very low, while it is much higher when subjected to the airstream of an air blower to remove excess chocolate, leading to different viscosities.
As its flow behavior depends on a number of interrelated factors, a number of approaches can be taken to modify the rheology of chocolate and optimize processes:
- The cocoa butter content has a major impact on the flow behavior of chocolate as its increase is responsible for the increased distance between the solid particles. This will lead to a decreased viscosity and a decreased yield value, or minimum shear stress required to induce a movement of the fluid. The fat content depends itself on the recipe and can be affected by any reformulation aimed at a fat reduction.
- The particle size distribution of the solid particles affects the amount of fat necessary to coat the solid particles. For instance, finer particles will need more fat to coat them and counteract the increased yield value caused by the increased interactions between particles.
- The moisture content is usually kept at levels inferior to 2%. The presence of water will make it very thick as sugar molecules will bind together, therefore largely increasing the yield value.
- As mentioned earlier, the role of conching is to develop the flavor of chocolate. It is a processing step that helps decrease the moisture content in the liquid chocolate and therefore its thickness. During conching, the freshly broken particles are also coated with fat which consequently reduces the interactions between particles.
- Emulsifiers like soy lecithin or polyglycerol polyricinoleate (PGPR) are usually added to chocolate as they act as surface-active agents at the interface between the hydrophilic sugar particles and the continuous hydrophobic fat phase. They once again contribute to the reduction of interaction between the solid particles in chocolate.
- All sugars and bulk sweeteners are not the same in chocolate applications. They can have an undesirable cooling effect and different degrees of relative sweetness and they may also exhibit a high solubility or a low melting point, as well as containing water of crystallization which results in gritty agglomerates and an unpleasant mouthfeel.
You can read the whole story in our May/June print edition of European Baker&Biscuit magazine.