AquaLab 8 SAMPLE PREPARATION
This increases the surface area of the sample, thus decreasing read-
ing times. However, keep in mind that modifying some samples may
alter their water activity readings.
For example, a candy may have a soft chocolate center and a hard
outer coating. The water activity reading for the center and the outer
coating are different, so one would need to evaluate which part of the
sample needed to be measured before crushing it. When the candy
is crushed, the water activity represents the average water activity of
the entire sample; whereas leaving the candy whole gives a reading
for the coating, which may act as a barrier to the center.
8.3 Slow Water-Emitting Samples
Some extremely dry, dehydrated, highly viscous water-in-oil (but-
ter), high fat, or glassy compositions may require multiple tests due
to their slow water-emitting properties. This is because the slow
emission of water decreases the change in water activity sufficiently
that the instrument determines the test to be complete, even though
changes in water activity are still occurring. The most effective way
to test these types of samples is to run them in the AquaLab using
the continuous or custom mode and wait for the water activity read-
ings to stabilize.
For faster reading, it is important to have the water activity of the
chamber at or below the water activity of these type of samples. This
causes the sample to release water to the vapor phase and equilibrate
with the chamber. If the water activity of the head-space is greater
than this type of sample, the sample requires a long period of time
to reach equilibrium and this delay may affect the water activity of
the sample.
8.4 Volatile Samples
The AquaLab gives accurate readings on most samples. However,
samples with certain volatiles in high enough concentrations may
give inaccurate water activity values. This is because the volatiles
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