as factors. The experimental variables measured were chosen from the main characteristics that describe unmoulded chocolate. A complete
second-order model was fitted to the experimental data. The most significant coefficients were that of energy consumption, iron
content and particle size. Optimization consists in a bound minimization of refining time using the desirability function. Before experiments,
working conditions were 70 rpm for as and 55 min for rt. The optimum conditions calculated by optimization were as follows:
58 rpm for as and 38.5 min for rt. The new working conditions identified for the ball mill considered enabled to rise output from 109 kg/h
to 156 kg/h, with a 43% increase in productivity. A control experiment carried out in the optimized conditions to corroborate the results
obtained, confirmed calculated expectations of response variables.
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

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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