Post-processing fat (re-)crystallisation in chocolate is a complex
phenomenon, in part driven by composition and storage conditions.
The presence of MF is beneficial in preventing fat bloom,
but only beyond a critical concentration, >2.5% of the finished
product. Below this level, MF still slows the form V?VI transition,
but appears to increase surface crystal growth when chocolates are
subjected to cycling. The addition of 5% MF is a suitable compromise
between maintaining the sensory properties of chocolate
and robustness to temperature-cycling.
This study also demonstrates that 2 crystallisation phenomena
concurrently take place in chocolate: (i) the growth of pre-existing
surface crystals that act as templates for larger bloom-causing
crystals and (ii) amorphous, welled regions (‘cones’) that solidify
with age and act as loci for crystal outcrops. The latter dominates
under constant temperature conditions whereas surface crystallisation
dominates with temperature fluctuations. Temperature-cycling
accelerates the growth of existing surface crystals through
repeated partial melting and solidification of the fat phase, with liquid-
state TGs promoting the growth of existing platelet crystals,
probably via a templating effect. In parallel, crystal growth appears
slower on the cones than on the background surface. It is feasible
that TG make-up of the cones differs from the rest of the chocolate,
which would help to explain their presence.
When viewed from an industrial, post-consumer purchase
viewpoint, it is best to think of microstructural evolution and fat
crystallisation in chocolate as a combination of both fluctuating
and isothermal storage, where surface crystallisation and cone
solidification occur concurrently.