Baking & Snack - May 2004 - 64

with the hydrogen ion (H+) from a leavening acid is straightforward:
HCO3 + H+ o H2O + CO2
The CO2 migrates to gas nuclei in the
batter and expands as it is heated, increasing the volume of the baking product.
Potassium bicarbonate (KHCO3) is
sometimes substituted for sodium bicarbonate to reduce the sodium content of
the ﬁnished product. Because of atomic
weight differences, 19% more potassium
bicarbonate must be used in making this
substitution. Thus, if a formula calls for
2.0% sodium bicarbonate, use 2.38% potassium bicarbonate to give equivalent
CO2 production.
Ammonium bicarbonate is used in some
low-moisture baked foods. This material decomposes at temperatures above
104°F (40°C):
NH4CO3 o NH3 + CO2 + H2O
The ammonia and CO2 are both gases, so
twice as much leavening action is obtained
per molecule compared with sodium or
potassium bicarbonate. The molecular
weight of ammonium bicarbonate is 94%
of that of sodium bicarbonate, so 1.88%
ammonium bicarbonate in a formula
yields twice as much leavening gas as 2.0%
sodium bicarbonate.
If the moisture content of the ﬁnished
product is greater than 5%, some ammonia
gas may be retained, giving an unpleasant
taste and aroma to the product. In eclairs
and popovers, both high-moisture products, the large internal volume and high
baking temperature allow the ammonia
to escape. Ammonium bicarbonate is used
mainly in cookies and crackers.

NUCLEATION
In preparing a dough or batter for a baked
product, the importance of nucleation
is sometimes overlooked. For any baked
product to rise properly and form desirable
crumb texture, the baker must incorporate
many small gas cells - usually air - into the

64 / BAKERS PRODUCTION MANUAL / May 2004

batter. These serve as nuclei for the leavening
gases generated during baking. The more
ﬁnely divided these air bubbles are in the
batter, the ﬁner the grain in the ﬁnal product.
Leavening acids such as cream of tartar
and MCP react at room temperature and
begin to generate CO2 while the batter
is being mixed. The action of the mixer
subdivides these bubbles of gas, forming
many nuclei for subsequent expansion
during baking. In soft batters such as pancake or wafﬂe batters where short mixing
time means that little air is entrained by
mixer action, this functionality promotes
an open grain in the ﬁnished product. In
cake batter and cookie dough, on the other hand, air bubbles incorporated during
creaming or early mixing stages form the
nuclei so the fast-acting leavening acids
are not needed.

REACTION RATES
Essentially all the sodium bicarbonate dissolves in the aqueous phase of the batter

ᮡ Many of today's most popular baked
foods take advantage of the gas generation
power of bicarbonates reacting with leavening acids.

ᮢ Rate of Reaction of Leavening Agents: Because the activity of leavening acids differs,
the baker can choose the effect desired, even
by blending slow- and fast-acting materials.
BAKERS PRODUCTION MANUAL

or dough by the end of mixing. The rate at
which CO2 is released is governed by the rate
at which the leavening acid dissolves and
generates hydrogen ions. When designing
a chemical leavening system for a particular
product, it is important to choose leavening
acids that react at various stages of baking to
achieve the desired ﬁnished product.
The design of the leavening acid system
for a baked food depends on the behavior
of the rest of the batter (or dough) system
during baking.
The chart, "Leavening Acid Reaction

Baking & Snack - May 2004

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