To enable proper mixing of the raw materials, the fat component must be permanently liquid and, consequently, heated. Adding a large quantity of cold ingredients to the hot fat may cause part of it to solidify, thereby impairing its lubricating performance.
Especially in the traditional method differences in temperature may be strongly present. To ensure good processing in the roll refiner, the mixer must produce a low-fat ‘dough’, with fat percentages varying between 18 and 25%, so only part of the fat is added at this stage.
Adding a large quantity of cold dry substances to a relatively small amount of fat may cause the whole mixture to solidify. A product cooled to too low a temperature may not leave the mixer until it has reached a temperature of about 40°C.
Furthermore, the paste may cool off on the conveyor belt when it is transported from the mixer to the roll refiner, which causes irregular product feed to the roll refiner and, consequently, the production of an unevenly refined inhomogeneous product.
Total systems machines are not capable of grinding at low fat levels, particularly due to the rapidly reducing degree of liquidity resulting from the larger particle surface that can be attained with this system. Nearly all the fat in the recipe has to be added at the beginning of the process, but this makes de-moisturising more difficult in the conching process. Solidification of the mass in the ball mill and centrifugal refiner is not likely to take place as the mixture is mixed and refined in a heated mill; actually, cooling is often necessary to reduce the temperatures increased by refining, to 40-60°C for milk chocolate (to prevent caramelisation) or 70°C for bitter chocolate.