Keywords: Chocolate; Ball mill refiner; Experimental design; Optimization; Desirability function
1. Introduction
The current European legislation (Dir. 2000/36/CE; UE,
2000) designates chocolate as the product obtained from
cocoa products and sugars, which contains not less than
35% total dry cocoa solids, including not less than 18%
cocoa butter and not less than 14% dry non-fat cocoa
solids.
The most traditional methods of chocolate-making are
based on the mixing of ingredients, grinding by roll refiners
(refining phase), conching, and tempering. Above all, conching
is carried out in order to remove moisture and undesirable
flavours while developing the pleasant ones. In
addition, since the previous grinding process will have created
many new surfaces not yet covered with fat, the conching
phase coats these new surfaces and improves the flow
properties (Beckett, 1999). The tempering process is a technique
of controlled crystallization that is necessary to
induce the most

stable solid form of cocoa butter (which
is a polymorphic fat) in the finished product (Talbot,
1999). Chocolate refining depends on product type (milk,
dark or compound), on process (crumb vs. milk powder)
and on ingredients (granulated or powder sugar). Grinding
operations may be evaluated on the basis of their costs
(capital, maintenance and energy) and the characteristics
with which they provide the product (particle size distribution,
particle shape and minimization of contamination).
The choice of equipment for size reduction depends on
many factors, including feed and final particle size, and
type of material being processed. Chocolate refining is
most often carried out using a five-roll refiner. Four grinding
rolls are aligned vertically, while the feed roll is placed
at an angle to the lowest stack roll. The feed rate determines
the throughput and the final fineness of chocolate,
and is adjusted by changing the feed roll gap at a constant