2009_Book_FoodChemistry

15.4 Baked Products 723
leavening is achieved by a sour dough formulation
which includes lactic and acetic acid bacteria.
15.4.1.6.1 Yeast
A given amount (Table 15.48) of surfacefermenting
yeast, Saccharomyces cerevisiae, is
used. While normal yeasts preferentially degrade
sucrose rather than maltose, special rapidly
fermenting yeasts are used which metabolize
both disaccharides at the same rate, shortening
the fermentation time.
Yeasts differ in their growth temperature optima
(24–26 ◦ C) and their fermentation temperature
optima (28–32 ◦ C). The optimum pH for growth
is 4.0–5.0. In addition to CO 2 and ethanol, which
raise the dough, the yeast forms a variety of
aroma compounds (cf. 5.3.2.1). Whether other
compounds released by the growth of yeast
would affect the dough rheology is unclear; there
appears to be no effect of yeast proteinase and
GSH.
carrier for phosphate-free baking powder. The
phosphate-free leavening mixtures produced on
an industrial scale contain citric acid or its acidic
sodium salt. In baking powder, the two reactive
constituents are blended with a filler which
consists of corn, rice, wheat or tapioca starch or
sometimes dried wheat flour. The filler content in
the powder is up to 30%. The role of the filler is
to prevent premature release of CO 2 .Themarket
also offers baking powders flavored with vanillin
or ethyl vanillin.
For every 500 g of flour, baking powder should
develop 2.35–2.85 gCO 2 , equivalent to about
1.25 liters.
In individual cases, NaHCO 3 alone is used for
some flat shelf-stable cookies and ammonium
hydrogencarbonate (NH 4 HCO 3 ) for many
others. Ginger and honey cookies are leavened
by NH 4 HCO 3 , mostly together with potash
(K 2 CO 3 ). To a small extent, a 1:1 mixture of
ammonium hydrogencarbonate and ammonium
carbamate (H 2 NCOONH 4 ) is used in some countries.
Both decompose above 60 ◦ CtoNH 3 ,CO 2
and water.
15.4.1.6.2 Chemical Leavening Agents
The interaction of water, acid, heat and chemical
leavening agents (baking powders) releases CO 2 .
The release of gas may occur in the dough prior
to or during oven baking. The agents consist of
aCO 2 -generating source, as a rule sodium bicarbonate,
and an acid carrier, usually disodium dihydrogendiphosphate,
sometimes monocalcium
phosphate [Ca(H 2 PO 4 ) 2 ]. Glucono-δ-lactone or
tartar (acidic potassium tartrate) are used as acid
Table 15.48. Amount of yeast used in bread and other
baked products
Baked product
Yeast added a
(%)
Rye bread 0.5–1.5
Rye mix bread 1.0–2.0
Wheat mix bread 1.5–2.5
Wheat bread 2.0–4.0
Breakfast rolls 4.0–6.0
Rusk (“Zwieback”) 6.0–10.0
a Based on flour content.
15.4.2 Dough Preparation
15.4.2.1 Addition of Yeast to Wheat Dough
15.4.2.1.1 Direct Addition
Flour, water, yeast, salt and other ingredients are
directly mixed into the dough.
15.4.2.1.2 Indirect Addition
Yeast is propagated at 25–27 ◦ C in a well-aerated
liquid pre-ferment which contains flour, water
and some sugar. After a given time, the liquid
is blended with the bulk of flour and water and
other ingredients and then made into a dough in
amixer.
For continuous indirect addition of yeast, special
liquid starters (sponges) with a pH of 5.0–5.3
are also used with incubation at 38 ◦ Ctodevelop
aroma. Such matured fermented sponge is then
metered continuously into a kneader which handles
the dough.