Baking & Snack - October 2005 - 79

October 2005

Managing Moisture
BY CLYDE E. STAUFFER, PH.D.
ater is a key ingredient in
baking. Without water, the
protein in wheat flour cannot
be developed into the viscoelastic
matrix that results in bread. Water plus
heat gelatinizes the starch granules in a
batter to form the structure of cake. And

a minimum AW of 0.93, while Penicillium (green mold) will grow at AW 0.82
and Aspergillus (yellow mold) at 0.83.
Bread is an ideal substrate for these
microorganisms. We may think of it as
a "dry" product, but the AW of bread is
around 0.96. Cake and cake donuts are

By controlling water activity in doughs
and finished products, formulators can
enhance the shelf life, texture and eye
appeal of baked foods.
water, properly retained and controlled,
contributes to longer shelf life of the
finished baked product. Among other
things, management of water (moisture)
involves aspects of microbial control,
eating quality, stability and shelf life.
Each has implications for the others.

WATER ACTIVITY
Water, in any situation, has a tendency
to evaporate into the surrounding
space, generating water vapor. Because
of its importance to the success of
proofing, bakers are most familiar with
relative humidity (RH), the ratio of the
moisture content of the air at a given
temperature and atmospheric pressure
to its potential moisture content at
saturation under the same conditions.
A similar effect takes place within
packages. Water evaporates from the
product but remains trapped as a
vapor within the package. A product's
water activity (AW) is the ratio of the
vapor pressure of the water in the food
product to the vapor pressure of pure
water (always 1.00) and equivalent to
one-hundredth of the RH generated by
the product in a closed system.
This moist atmosphere has microbiological implications for baked foods
because molds and bacteria require
a certain minimum AW to grow. Most
pathogenic bacteria require AW to be at
least 0.94. Molds vary in the minimumrequired AW: Rhizopus (black mold) has

less favorable to microorganisms with
AW of around 0.86. Generally products
with moisture content of 14% or less
will not sustain mold growth, thus,
AW for cookies and crackers typically
runs 0.20 to 0.30.
When baked foods exit the oven
or fryer, they are sterile. But the atmosphere in a bakery is loaded with
mold and bacteria spores, and
these start to settle on the
product, hence the need for
anti-microbials such as calcium propionate to retard
the growth of microorganisms. Good bakery
sanitation reduces the
chance of spoilage,
but microorganisms
are always present.

depends on moisture content and temperature. Low water and low temperature speed it up; high water and high
temperature slow it down. While stale
bread gives the mouthfeel impression
of dryness, the water content has not
changed. So, longer shelf life is not simply a matter of better packaging; rather,
it depends in part on retaining water in
the baked product.
This means minimizing bake loss.
Most of the weight lost during baking
and cooling happens because water in
the dough evaporates. On occasion,
the oven operator will increase bake
time by a minute or so to get a more
desirable crust color. This also increases
bake loss and decreases shelf life. On
the other hand, the addition of soy flour
to dough raises
its absorption

MOISTURE
RETENTION
High water content
extends the shelf life
of bread and cake by
retarding staling. The
main cause of staling is
the recrystallization (retrogradation) of gelatinized
starch granules. This process

ᮣ Humectants such as hygroscopic
sugar alcohols prevent syneresis in
meringue pie toppings.

October 2005 / BAKING & SNACK / 83

Baking & Snack - October 2005

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