Liberation of fat from milk powder particles during chocolate processing through moisture-induced lactose crystallisation

The amount of fat in the continuous phase significantly affects chocolate mass viscosity and is therefore important for processing steps where viscosity plays a prominent role, for example moulding. The aim of the present study was to evaluate whether a mechanical pre-treatment of chocolate ingredients including spray-dried whole milk powder induces the crystallisation of amorphous lactose and leads to the release of fat that is entrapped in milk powder particles. Laboratory scale experiments showed that small amounts of water that was added during mixing of milk powder changed the state of lactose which, in turn, triggered the liberation of fat. The progress of these changes is significantly affected by duration of the mechanical treatment, and treatment temperature. In pilot scale chocolate production, it was possible to generate similar effects with a process-integrated mechanical pre-treatment of ingredients in a conch and subsequent refining in an agitated bead mill. Comparative measurements showed that the effects of water addition and mechanical treatment on chocolate mass viscosity are equivalent to the addition of approx. 3 g/100 g cocoa butter. •Water addition to milk powder and mechanical treatment induces lactose crystallisation.•Lactose crystallisation intensity depends on treatment temperature and time.•Lactose crystallisation triggers the release of entrapped fat from whole milk powder.•Similar effects are obtained when chocolate ingredients are mechanically treated prior to conching.•Treatment helps to save cocoa butter during processing but does not affect sensory properties.