3.2. Influence of the ice cream temperature at the SSHE
exit on the ice crystal structure
In the case ofco oling conditions above the initial
freezing temperature, the mix was only whipped on the
scraped heat exchanger surface, without any ice nucleation
and ice freezing. The electron microscopy (Fig. 5a)
showed a dentritic-type pores structure after the ice
sublimation confirming the structure observed with the
direct method (Fig. 5b). Besides, with the destructive
microscopy method (Fig. 5c)—method not really suited
for large particles—we observed some important ice
crystals agglomeration, so that the quantitative size
analysis was very difficult to carry out.
By contrary, operating the freezing in the SSHE
below the mix initial freezing temperature generated ice
nuclei and consequently small ice crystals in the final
product. In this case, the three methods—scanning
electron microscopy (Fig. 6a), direct microscopy
(Fig. 6b) and destructive method (Fig. 6c)—led globally
to the same qualitative conclusions.
In the same way, we also investigated the influence of
the hardening temperature—i.e. the air temperature in the
cold room—on ice crystal shape and size structure by the
direct optical microscopy method. As expected, decreasing
the hardening temperature led to a reduction ofic e
crystal mean size by limiting the recrystallization phenomena
(Miller-Livney & Hartel, 1997; Cogn!e, 2003).