25 Rye Constituents and Their Impact on Rye Processing 583against spoilage by mold growth, thereby improving
product shelf life (Meuser et al. 1994, Poutanen
1997, Seibel and Brümmer 1991). When sourdough
is used in wheat bread making, its main function is
to improve sensory properties and to prolong shelf
life (Brümmer and Lorenz 1991).
Mixing and Kneading Rye flour, yeast, salt, and
water are optimally mixed and kneaded with sour-
dough, lactic acid, or lactic and acetic acid to form a
viscoelastic dough. The level of water is that yield-
ing the required dough consistency. Rye doughs
have to be mixed slowly because of their high arabi-
noxylan content, which leads to tough doughs when
the energy input is excessive. The optimal mixing
time depends on the composition and enzymic
activities of the rye flour (Seibel and Weipert
2001a).
Important dough quality characteristics are dough
yield, that is, the amount of optimally developed
dough obtained from 100 g flour, and dough struc-
ture.
Fermentation Mixing and kneading of the dough
is followed by a floor time. Thereafter, the dough is
divided into pieces, which are molded by hand into
the desired shape. The doughs are then proofed to
their best potential. Fermentation takes place at 30–
36°C and 70–85% relative humidity. Fermentation
time depends on the composition of the flour, the
activity of the flour enzymes, the dough formula-
tion, and the fermentation temperatures.
During fermentation, carbon dioxide is produced,
and the gas is retained by the dough, resulting in a
volume increase of the dough. Although the rate of
gas production in rye flour dough is high, the gas-
retaining capacity is low, resulting in dense, com-
pact loaves (He and Hoseney 1991).
Baking After fermentation, the dough is placed in
an oven and transformed into bread. Bread quality
depends on baking temperature, uniformity of tem-
perature in the oven, and baking time. Optimum
baking temperature and time depend on the weight
of the dough pieces and the shape of the loaves,
which determine the rate of heat transfer. In rye
bread making, at the beginning of the baking stage,
steam is often used in the oven to develop good crust
characteristics (Seibel and Weipert 2001a).
Important bread quality characteristics are specific
volume, crumb structure, crumb elasticity, crumb
firmness during storage; and sensory properties such
as taste, flavor, and odor.Impact of Rye Constituents on Dough and
Bread Quality CharacteristicsDifferent rye varieties show highly different bread-
making quality as influenced by harvest year and
genotype (Hansen et al. 2004, Nilsson et al. 1997b,
Rattunde et al. 1994). This can be attributed to sig-
nificant differences in the content and structure of
the major rye constituents, which are influenced by
both factors (Hansen et al. 2003).Starch Starch gelatinization and -amylase activ-
ity are very important parameters for the bread-mak-
ing quality of rye flour. Both properties can, for
example, be measured by the falling number method
or the amylograph test. The falling number is in-
versely related to -amylase activity. An important
parameter in the amylograph test is amylograph
peak viscosity, which is correlated positively with
starch content and negatively with -amylase activi-
ty. It should be noted, however, that arabinoxylans
can influence falling number and amylograph char-
acteristics of rye flours. At similar -amylase activi-
ty levels, higher falling numbers (Weipert 1993a,
1993b, 1994) and higher amylograph peak viscosi-
ties (Nilsson et al. 1997b) can be measured due to
higher arabinoxylan contents. The arabinoxylans in-
crease the viscosity, but also protect the starch gran-
ules against enzymic breakdown by hindering and
retarding the activity of-amylase (Weipert 1993b,
1994).
For rye bread-making suitability, a minimum
starch gelatinization temperature of 63°C and, under
specified experimental conditions, a minumum amy-
lograph peak viscosity of 200 amylograph units
(AU) are required. Rye shows optimal bread-making
quality at a starch gelatinization temperature of 65–
69°C and an amylograph peak viscosity of 400–600
AU (Weipert 1993a). Maximum bread-making qual-
ity is associated with intermediate values of falling
number (Rattunde et al. 1994). Rye flours with high
-amylase activity give a soft, sticky dough, which
may be too fluid to process into bread or results in a
doughlike crumb. Therefore, preharvest sprouting,
which goes hand in hand with high -amylase activ-
ity, is disadvantageous for rye flour quality. Rye
flours with low -amylase activity yield a rigid, sta-
ble dough but lead to breads of low volume having a