Slow Water-Emitting Samples - Decagon Devices AquaLab 4TE Operator's Manual

AquaLab
8. Sample Preparation
Coated and Dried Samples
Samples with high sugar or fat coatings often require multiple read-
ings, because it takes longer for them to equilibrate. If this is the
case for your samples, it is not a problem with your instrument; it
simply means that your particular sample takes longer than most to
equilibrate.
To reduce the time needed to take an water activity reading for coat-
ed or dried samples, you can crush or slice the sample before sam-
pling. Th is increases the surface area of the sample, thus decreasing
reading times. Keep in mind, however, 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. Th e water activity reading for the center and the outer
coating are diff erent, 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 will represent the average water activity of
the entire sample; whereas leaving the candy whole will give a read-
ing for the coating, which may act as a barrier to the center.

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. Th is is because the slow
emission of water decreases the change in water activity suffi ciently
that the instrument determines the test to be complete, even though
changes in water activity are still occuring. Th e most eff ective way to
test these types of samples is to run them in the AquaLab using the
continous or custom mode and wait for the water activity readings
to stablize.
48