Chemistry Reference
In-Depth Information
0.7
0.6
0.5
0.4
0.3
0.2
Packed at 40
°C
Packed at 35 °C
Packed at 30 °C
0.1
0
0
5
10
15
20
25
30
Temperature (°C)
Figure 4.4.
Graph showing the hot packed temperature, the cold storage temperature and
water activity combinations that lead to relative humidity conditions in the bed exceeding 80%,
which precedes caking (from Paterson and Bronlund, 2009, with permission.).
Figure 4.4 shows a graph that has been produced based on the model
developed by Paterson and Bronlund (2009) and it shows that if a product is
packaged at 408C and then placed in a warehouse at 108C for storage, in order
to avoid caking, the water activity of the powder must be below 0.32. The
figure can also be used as a guideline for the target water activity to be
achieved in the dryer in order to prevent caking during transport. To use
Figure 4.4 in this way, one assumes that the entire bag is heated to the
maximum temperature and then has the outside of the bag subjected to a
cold environment. It is obvious that provided the final product has a water
activity below 0.3, no caking should occur under most conditions that are
likely to be encountered during transport from cold to hot climates, such as
when product is shipped across the equator.
The KELLER
TM
edible lactose process is the most common turnkey
lactose plant. It is marketed by Relco of the USA (
http://www.relco.net
). It
follows the traditional path, with a concentration leaving the evaporator of
about 58% TS. The cooling curve with time is considered confidential and is a
key part of its success. By controlling the cooling curve in the standard Keller
design crystallisers, it is possible to control nucleation to produce the right
number of crystals, allowing growth of optimally sized crystals for the wash-
ing and recovery section of the plant.
To summarise, the main objective of plants producing edible-grade
lactose is to achieve the maximum yield. The main parameters are to have
the solids level exiting the evaporator as high as possible and to cool the batch
to as low a temperature as can be achieved. But it is critical to control
-lactose
