An investigation has been carried out into the rheology of
chocolate in relation to its flow and mixing features in a real
industrial environment. The chocolate manufacturing plant of
Rowntree at York provided a base for this study.
The project aims were:
a) to measure the viscous and time dependent properties of
chocolate.
b) to explain the observed flow properties in relation to the
constituents of chocolate.
c) to determine the shear rate which, for a given recipe,
yields a minimum stable viscosity (of particular commercial
value).
d) to assess the type of mixer able to provide this duty.
The experimental work involved rheological studies with concentric
cylinder and tubular viscometers, operated to measure viscosity as
a function of shear rate and shearing time.
The chocolate samples studied were taken from various points in the
manufacture process at Rowntree, York. Model chocolate systems were
made from cocoa liquor, and sugar with cocoa butter, which were
studied to underpin the basic mechanisms of the flow properties of
the total chocolate.
Shear thinning in milk chocolate has been shown to be accounted for
by surface coating and fat release from the cocoa cellular
material.
Analysis of the sugar and cocoa butter system gave large hysteresis
loops which may be explained as due to agglomeration of the sugar
particles. The level of hysteresis was found to be related to the
polarity of the liquid phase, such that a more polar fluid results
in less hysteresis.
Laboratory experiments have revealed that the level of work input
to give permanent viscosity reduction for milk chocolate is
dependent on the measuring shear rate. The level of optimum shear
input for the measuring range 10 to 130 sec
1 is 645 sec for 30
minutes. The apparent viscosity measured at lower shear rates
requires much longer ([approx]100 minutes). / Yorkreco, Nester York Ltd.
| Identifer | oai:union.ndltd.org:BRADFORD/oai:bradscholars.brad.ac.uk:10454/4200 |
| Date | January 1989 |
| Creators | Rutson, Sandra M. |
| Contributors | Benkreira, Hadj, Beckett, S. |
| Publisher | University of Bradford, Postgraduate School of Studies in Chemical Engineering. |
| Source Sets | Bradford Scholars |
| Language | English |
| Detected Language | English |
| Type | Thesis, doctoral, PhD |
| Rights | <a rel="license" href="http://creativecommons.org/licenses/by-nc-nd/3.0/"><img alt="Creative Commons License" style="border-width:0" src="http://i.creativecommons.org/l/by-nc-nd/3.0/88x31.png" /></a><br />The University of Bradford theses are licenced under a <a rel="license" href="http://creativecommons.org/licenses/by-nc-nd/3.0/">Creative Commons Licence</a>. |
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