In general, less fat was required to inhibit bloom on chocolate chips
baked in sand–fat mixtures compared to chocolate chips baked in
cookies. For example, while 18–19% palm oil shortening was necessary
to inhibit bloom on chocolate chips baked in cookies, as little as
8% palm oil shortening inhibited bloom in the sand system. One reason
for the disparity between the fat levels needed to inhibit bloom in
cookies and sand-fat mixtures may be due to differences in the physical
structure of the two systems. Cookie dough is a denser medium
with a more complex microstructure than sand. Liquid fat may more
readily migrate through sand due to the homogeneity of the system
and larger particle size, resulting in more fat migration into the chocolate
chip. As a result, less fat in the sand was required to inhibit
bloom. In addition, the chocolate chips baked in sand reached higher
temperatures and melted faster than chocolate chips baked in cookie
dough, meaning chips baked in sand spent a longer time in the molten
state during baking, which also resulted in more total oil migration.