In the following processing step the conched chocolate is given its required fluidity, or, as it is called, brought to specification. Close to the end of the conching process, which is different for each manufacturer, an emulsifier is added, virtually always soya lecithin, for binding the moisture still present in the chocolate. The effect is remarkable: the thick seemingly dry material produced by the conche changes into a smoothly flowing material. The added emulsifier reduces the shear stress, thereby enabling the chocolate to be pumped to the chocolate tank, where it is given its specific flavour.
It is very important that the lecithin is distributed homogeneously in the chocolate, so it should be mixed with a small amount of liquid cocoa butter or another fat.
Many chocolate manufacturers add all or part of the lecithin in the recipe to the chocolate at an earlier stage, some even adding it to the product in the kneader/mixer, others feeding it in with the product into the conche. This can be necessary, depending on the process, but it will cause the moisture to evaporate less easily and, consequently, impair the conching performance.
Consequently, end products manufactured from the same recipe, may have different rheological properties and must be brought to specification at the end of the process, usually by adjusting the viscosity and the yield value. Mostly cocoa butter is added and the remaining percentage of cocoa liquor (cocoa liquor is fine; it need not be conched along with the chocolate and it can influence the chocolate flavour by adding it at a later stage).
Not only fat (cocoa butter), but also emulsifiers can be used to modify the rheological properties; cocoa butter is one of the more expensive components of chocolate.
The viscosity of the product is important to be able to pump the chocolate, while the yield value is an indicator of its spontaneous fluidity. Their combined action is called rheology or the science of the flow of matter. The quantity of fat to be added can be calculated based on rheological measurements.