Why is roller/drum dried milk powder more functional than the alternatives?
The beneficial rheological effect observed for roller-dried milk powder in comparison with spray dried powder has been attributed to both the higher level of free fat and the large particle shape of the roller dried powder.
Roller dried whole milk powder is more functional in chocolate than spray dried milk powder because approximately 90% of the milk fat is free as compared to 2-3% for spray dried. The net result of this difference is that milk chocolate made from spray dried milk powder requires the use of 2-3% more, expensive cocoa butter to maintain the handling properties during manufacturing and the mouth feel of the finished product. It is well known that confectionery manufacturers prefer the rheological benefits that roller-dried powders can provide over spray dried powders.
Powder that contains high free fat that is easily extractable and can interact directly with the cocoa butter in chocolate typically has been desired by milk chocolate manufacturers. The high free fat level results in reduced chocolate viscosity, making it easier to process the chocolate and providing an economy in cocoa butter savings as cocoa butter is usually added in the conch to control viscosity.
Characteristics such as particle size, density, and internal structure influence the processing conditions needed to make chocolate. The size of particles in chocolate after refining (particle reduction) plays an important role in product viscosity. If particles are small, viscosity is high and additional fat is needed to coat these fine particles to reduce viscosity. Roller milk powder has large particles. The strength of the particles, their shape, and the amount of air included in void spaces (vacuole volume) has an impact on the shattering aspects of powder particles and influence chocolate properties (fluid rheology and mechanical properties of the solidified product). It has been verified that powders with high vacuole (air) volume led to high chocolate viscosity, due to the effect of breakage into small particles that must be covered with fat. In spray whole milk powder, particles are spherical and may be agglomerated. They contain bubbles or vacuoles which increase the porosity and reduce density. Roller-dried particles, on the other hand, are flakes without vacuoles.
Furthermore, the energy consumption is reduced in the conch when using roller because it runs wetter than with recipes using spray milk powder. The tempering temperature is lower when using roller because of the higher amount of crystallized lactose in roller milk.