Campden BRI Talks Chocolate Production Optimization

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

Chocolate is typically mostly composed of sugar, cocoa mass and cocoa butter. It can also include milk powder thus constituting milk chocolate. Each ingredient in chocolate has a functional role. For instance, cocoa mass and cocoa butter deliver the rich cocoa flavors. They also provide the fat that is so valuable in creating the unique texture of chocolate through the tempering process. Additionally, sucrose acts as a sweetener and bulking agent. Chocolate therefore usually has a high energy content as its nutritional composition is rich in sugars and fat. The World Health Organization has estimated that the prevalence of diseases like obesity and diabetes has increased by nearly three and four times respectively over the past 40 years and could, in some cases, be attributed to the high consumption of energy-dense, fat- or sugar-rich products. This phenomenon has led to pressure on food manufacturers, from public health stakeholders and consumers, to reformulate products like chocolate to reduce calories, fat or sugar. Nevertheless, the composition of the chocolate is one of the many factors affecting its quality and processability.

The Chocolate-making Process

Chocolate-making is a long and complex process. It starts with the cocoa pods that are harvested from the cocoa trees grown mainly in West Africa, South America and Indonesia. The beans are subsequently freed from the pods and fermented to develop chocolate flavor precursors. The fermentation process must be tightly controlled to prevent the generation of undesirable flavor precursors that cannot be eliminated at later stages. Among the parameters affecting the fermentation of the beans the most important ones are the maturity of the harvested pods, the storage time prior to fermentation and the aeration of the fermenting beans.

After fermentation, the drying of the beans is another critical step. Quick drying can result in very acidic beans, and unwanted smoky notes can be generated through artificial drying using wood fires. The dried cocoa beans can be roasted whole, after being cracked into nibs or ground into liquid cocoa mass. With each cocoa material, the aim of roasting is the same – to reduce the acidity of the cocoa and increase the intensity of the cocoa aroma. However, the energy input required and the homogeneity of the roasting level will differ – roasting the liquid cocoa mass is faster and delivers more homogenous results. The cocoa mass will be destined for use as an ingredient to make chocolate, or for pressing. Pressing involves the separation of fat (also called cocoa butter) from the cocoa press cake, which is then ground into cocoa powder.

When used for making chocolate, the roasted cocoa mass is mixed with additional cocoa butter and sugar, with or without milk powder, and refined down to less than 30 microns to avoid any grittiness. Afterwards, the refined chocolate is then subjected to conching (or agitation) with more cocoa butter to remove the undesirable flavors and develop the pleasant ones generated during the previous stages. The refined chocolate finally goes through the tempering process. It aims to form stable fat crystals after an appropriate thermal treatment to give the chocolate its solid texture at ambient temperature and glossy appearance.

The Importance of Chocolate Flow Behavior

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 soya 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.

How Process Modelling Can Help

Finite element modelling (FEM) can be used to model the behavior of fluids like chocolate in real life situations. It allows multiple situations to be modelled quickly and cheaply to solve problems, optimize food and drink processes and assess the effects of changes. The 3D physical modelling capability is very flexible and is suitable for a variety of situations. For instance, the flow of chocolate through a pipe, or while it is being mixed, could be easily modelled using the flow behavior data collected from various reformulated chocolate recipes. This could, for instance, be used to quickly evaluate the impact of the reformulation on the required energy to transfer the liquid chocolate from the conche to a storage tank or a tempering unit, or as it is molded, or enrobing a product. Once the situation has been modelled, potential solutions can be identified to modify the recipe further or optimize the process parameters.

Developing or reformulating chocolate products can be challenging. Not only does it impact the compositional and flavor profile of chocolate, but it may also alter its flow properties that are critical for processing. Finite element modelling can be used to predict it in different scenarios and identify potential issues and solutions. It can help developers scale up the production of novel or reformulated chocolate products from a pilot scale to a larger production scale.