Chemistry Reference
In-Depth Information
Figure II.1.
Batch production of dulce de leche in open kettles. Adapted from Zalazar (2003).
transferred to the evaporating kettle. The volume in the kettle is low initially
(20% of its capacity); when boiling has caused some concentration, the rest of
the blend is fed slowly into the kettle while boiling continues. A stirrer fitted
with heat-resistant plastic scrapers is used to prevent the product sticking to
the wall of the kettle and to improve the release of vapour from the hot mass
of DL. As the solids content increases, Maillard and other non-enzymatic
browning reactions occur and the product attains its typical colour and
flavour. Cooking is stopped when the solids content is 68%, which is assessed
by refractometry. Legislation requires 70% total solids but this target value is
normally attained during the following steps of the process, discharge of hot
DL and cooling. After that, the product is pumped to a homogenizer, where it
is homogenized to avoid clumps and improve texture. Finally, the product is
packaged while still hot (608C), to avoid microbiological contamination, in
plastic containers (0.25, 0.5 and 1 kg). Glass containers are also used but they
are not very common and are usually reserved for premium DL. Paste-board
packages of 10 or 20 kg are used for bakery and confectionery purposes.
In the semi-continuous process, the mixture of sugar and milk is con-
centrated in a multiple-effect evaporator to improve the efficiency of the
evaporation step; afterwards, the final solids content is obtained by boiling
in the open kettle, where the colour and flavour develop. In the continuous
process there is an inversion of the steps, as colour development is first
