Chemistry Reference
In-Depth Information
0°C 32°F
Heat shock
(melting and refreezing
water by raising and
lowering the temperature)
-4 25
Draw temperature
a
-8 18
-12 10
Mix A
(lower concentration
of sugars and/or
higher mol. wt.)
Mix B
(higher concentration
of sugars and/or
lower mol. wt.)
Re
t
a
il
cab
i
net
temperature
b
-16 3
-20 - 4
y
x
-24 -11
10
20
30
40
50
60
70
80
Percentage of Water Frozen
The lower the freezing curve, the less water frozen at drawing from the barrel
freezer (30% for mix B compared to 45% for mix A), hence more water to freeze
out during hardening, which is the slower process yielding larger ice crystals.
The lower the freezing curve, the softer the ice cream in the retail cabinet (60%
water frozen in mix B compared to 75% for mix A), hence more susceptible to
heat shock.
In looking at freezing curves, on the flatter part of the curve (warmer temperature
range), a given temperature change (e.g., 4°C) involves more water melting and
refreezing (hence more recrystallization), while on the steeper part of the curve
(lower temperature range), the same temperature change involves less water
melting and refreezing (less recrystallization); for mix A, a b but x > y.
Figure III.3.
Typical freezing curve for ice cream mixes of varying composition showing the
percentage of water frozen at various temperatures.
Cindio et al., 1995; Livney et al., 2003; Whelan et al., 2008). The significance
of freezing point depression and freeze-concentration is that it dictates the
harness of the ice cream as a function of temperature. In scooping or retailing
operations, it is extremely important to have all ice creams close to the same
degree of hardness. Hence, formulations must be adjusted to account for
variable levels of sugars and/or types of sugars to ensure constancy in
hardness.
Lactose is not very sweet and is contributed by the MSNF ingredients,
as discussed above, rather than being considered as a sweetener. Nevertheless,
an excess of lactose, for example with a high concentration of whey powder,
can lead to ice cream that is too soft for typical storage/distribution tempera-
tures and retail operations. As the amount of unfrozen water increases, the ice
cream becomes more prone to problems like ice recrystallization and the
development of coarse or icy textures, more prone to lactose crystallization
