Water activity measurements can help to prevent qualityrelated
problems such as mould growth and adverse
changes in taste and texture. They can also avoid wastage
of ingredients and energy, as Labcell explains

Water activity is a versatile quality
metric in the food, pharmaceutical
and cosmetic industries and it is
applicable at several different points within
the overall production process. To maximise
the benefits available from water activity
measurements, the research and development
(R&D) department should first use water
activity and moisture sorption isotherms to
formulate the product in order to optimise the
taste, texture, packaging, safety and shelf life.

Whereas water activity is a measure of the
energy status of the water in a component
(eg an individual ingredient) or system (eg a
complete food product), a moisture sorption
isotherm is a graph of the relationship
between water activity and moisture content
(as a percentage) at a specific temperature;
sometimes a set of isotherms will be
generated at different temperatures to
characterise more fully the component or
system. The specifications created by the
R&D scientists can then be used as the basis
for the acceptable limits elsewhere in the
production environment.

For example, incoming ingredients can have
their water activity measured as part of the
acceptance procedure. Isotherms will provide
information to indicate whether a given
activity will cause spoilage during storage,
thereby helping to eliminate waste and
ensure that storage conditions are optimised.

Once ingredients enter production,
managers can monitor the water activity and
adjust parameters such as temperatures to
ensure that products are not over- or
undercooked. Further measurement of water
activity by quality assurance and quality
control personnel can verify that every batch
complies with all product specifications.

For instance, R&D scientists are likely to
have specified HACCP (Hazard Analysis and
Critical Control Point) water activity
specifications. Further water activity
measurements can be used prior to shipping
to ensure batches are within specification
before being delivered to customers – who
may also have specified upper and lower
limits for water activity
Water activity can be used by managers to
gain an insight into the performance of the
production plant. As an accurate scientific
metric, water activity can provide reliable
data for evaluating a plant’s performance,
thereby helping to raise efficiency and reduce
variation and waste.

Instruments manufactured by Decagon
Devices for measuring water activity and for
generating isotherms are simple and quick to
use. The phrase used by the company is ‘If
you can microwave a burrito, you can run a
highly accurate water activity test’. Highresolution
moisture sorption isotherms are
similarly straightforward to generate, and the
Decagon instruments can complete this
process in two days, which is considerably
quicker than some traditional methods used.

Labcell is UK distributor for water activity
instruments manufactured by Decagon
Devices. Data sheets can be downloaded
directly from Labcell’s website: www.labcell.

com or contact the company to request a
copy of the new ‘Managing by Water
Activity’ booklet.