Stresses in the Drying of Food Doughs
In the last two decades, a number of papers have been published
presenting experimental results about various aspects of the processes
occurring during the drying of food doughs and, in particular, pasta and
noodles. The purpose of the current research is to indicate how these results
can be combined and re-interpreted to construct a conceptual four-phase model
of the drying of pasta. In addition, it is shown how each of the four phases
can be related to four phases in the movement of free and bonded water, as
drying progresses.
This conceptual model yields a framework in which the construction of
comprehensive mathematical models of the drying can be undertaken in the
future. Such a four-phase model is consistent with circumstantial evidence in
classical texts describing the various phases in the industrial drying of
biomaterials, though most texts only identify three phases because they lump
the initial evaporation of surface moisture with the subsequent saturated
drying.
One is led to the conclusion that, historically, the drying of pasta has been
more art than science, and that the traditional concept of a “three phases
drying” process has evolved by trial-and-error. Recent publications can be
seen to provide a more formal scientific basis for the existence of the
mentioned four phases. From the context of manufacturing high quality pasta
rapidly (in high or ultra-high temperature dryers), a key question concerns
how one should model the stresses generated in food doughs as the drying
progresses through the four phases.
The starting point for the research being performed in the Mathematical
Modelling of Industrial Processes group in CSIRO Mathematical and Information
Sciences is the assumption that it is the porosity within the pasta, along
with the nature and amount of free and bonded water, that determines how a
pasta will react to a give drying scenario. It has led to the formulation of
models for each of the four phases in terms of the movement of the free and
bonded water in the pasta, as the drying progresses. A summary of this
approach can be found in the attached
"poster".