Food products may lose quality if the moisture
level changes from the equilibrium moisture in the
distribution chain. The rate of moisture change can
be monitored by changes in package weight which
occur during storage in appropriate temperature and
humidity environments. Medallion Laboratories has
computerized this old technique and applied it to a
wide variety of food products. For products that suffer
quality losses in high humidities, the packages are
stored in what is known as the “weather room”. This
room is kept at constant 65% RH with temperature
cycling on a day/night basis between 90°F and
74°F. These conditions are used to simulate the hot,
humid summers of the southeastern United States.
The packages are weighed back at weekly intervals
and the gain in weight, along with the original
moisture determination, are then used to calculate
the moisture changes. From the moisture sorption
curve developed for the product and knowledge of
the package material water vapor transmission rate
(WVTR), a calculation can be made to determine its
shelf life.
It is difficult to obtain reliable weight change data
on packages at relative humidities above 75%.
Most food packages contain paper or paperboard
which gain and lose moisture in the same manner as
food products. When stored at a relative humidity
above 75%, the amount of water gained for the
paper component with a small change in humidity
is large and moisture condensation also becomes a
problem.
The package weight method is ideal for comparing
variations where only small differences are expected.
This method has been able to show moisture changes
due to a few pinhole leaks in impermeable pouches.
To obtain reliable results, there are some
prerequisites:
1. Initial product moistures must all be the same in
each set.
2. Sealed empty packages must be used as controls.
3. The heat and humidity at the storage conditions should
not result in weight changes other than from moisture,
i.e., no chemical changes in leavening systems.
4. The weight variation of the packages must be small
with respect to net product weight. A rule of thumb
is that the weight difference between the heaviest and
lightest empty packages divided by the average net
weight of the product must equal 0.025 or less.
If moisture gain or loss is extremely important to the
packaged food product, this method may be able to help
you with shelf life questions.
Food products may lose quality if the moisture
level changes from the equilibrium moisture in the
distribution chain. The rate of moisture change can
be monitored by changes in package weight which
occur during storage in appropriate temperature and
humidity environments. Medallion Laboratories has
computerized this old technique and applied it to a
wide variety of food products. For products that suffer
quality losses in high humidities, the packages are
stored in what is known as the “weather room”. This
room is kept at constant 65% RH with temperature
cycling on a day/night basis between 90°F and
74°F. These conditions are used to simulate the hot,
humid summers of the southeastern United States.
The packages are weighed back at weekly intervals
and the gain in weight, along with the original
moisture determination, are then used to calculate
the moisture changes. From the moisture sorption
curve developed for the product and knowledge of
the package material water vapor transmission rate
(WVTR), a calculation can be made to determine its
shelf life.
It is difficult to obtain reliable weight change data
on packages at relative humidities above 75%.
Most food packages contain paper or paperboard
which gain and lose moisture in the same manner as
food products. When stored at a relative humidity
above 75%, the amount of water gained for the
paper component with a small change in humidity
is large and moisture condensation also becomes a
problem.
The package weight method is ideal for comparing
variations where only small differences are expected.
This method has been able to show moisture changes
due to a few pinhole leaks in impermeable pouches.
To obtain reliable results, there are some
prerequisites:
1. Initial product moistures must all be the same in
each set.
2. Sealed empty packages must be used as controls.
3. The heat and humidity at the storage conditions should
not result in weight changes other than from moisture,
i.e., no chemical changes in leavening systems.
4. The weight variation of the packages must be small
with respect to net product weight. A rule of thumb
is that the weight difference between the heaviest and
lightest empty packages divided by the average net
weight of the product must equal 0.025 or less.
If moisture gain or loss is extremely important to the
packaged food product, this method may be able to help
you with shelf life questions.
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