582 Part V: Fruits, Vegetables, and Cereals
is sticky and difficult to sift, generous sifting sur-
faces are required (Zwingelberg and Sarkar 2001).
Impact of Rye Constituents on Rye Milling
Rye contains higher levels of arabinoxylans than
wheat (Aman et al. 1997) and is accordingly more
difficult to mill. Because the arabinoxylans are hy-
groscopic, the flour absorbs ambient humidity and
tends to clump. This interferes with sifting. For this
reason, rye is milled at a lower moisture content and
requires more sifting surface than wheat (Zwin-
gelberg and Sarkar 2001).
Protein content also influences the performance
of rye in the mill. When it exceeds 12%, rye be-
comes more difficult to grind and has a lower extrac-
tion rate (Weipert 1993a).
RYEBREADMAKING
The bread-making behavior and performance of rye
differ considerably from those of wheat (Weipert
1997). The principal reason for this is that rye pro-
teins cannot form a gluten network, which lies at the
basis of wheat bread quality. In addition, rye starch
gelatinizes at a lower temperature than wheat starch
and is therefore more prone to enzymic degradation
during the oven phase than wheat starch. The main
differences between rye and wheat breads are ob-
served in terms of volume yield, crumb texture, and
shelf life. Baking volume of rye breads is normally
only about half that of wheat. However, rye bread
has a longer shelf life and is richer in taste and aro-
ma (Weipert 1997).
A wide assortment of rye-containing breads exists.
They vary in size, shape, formulation, bread-making
process, and sensory properties. Rye flour and
whole meal rye can be incorporated into rye bread
(minimum 90% rye), mixed rye/wheat bread (mini-
mum 50% rye), or mixed wheat/rye bread (mini-
mum 50% wheat). Other ingredients can be crushed
rye grains, malted and crushed rye grains, malted
rye kernels, or precooked rye kernels (Kujala 2004).
Examples of rye bread types are pumpernickel (con-
taining whole kernels), soft sourdough bread, crisp
bread, rolls, and buns.
Rye Bread-Making Process
For rye bread production, acidification is a prerequi-
site to obtain a good quality product. The traditional
method of preparing rye bread uses sourdough, al-
though sometimes, direct acidification by lactic acid
or other organic acids is used.Preparation of Sourdough Sourdough is classi-
cally made by mixing rye flour or whole meal rye
with water, yeast, and a starter and allowing the mix-
ture to ferment (Kariluoto et al. 2004, Meuser et al.
1994, Seibel and Brümmer 1991). As starter, a com-
mercial culture containing lactic acid bacteria or a
portion of previous sourdough, equally containing
lactic acid bacteria, is used (Seibel and Brümmer
1991). In homofermentative lactic acid fermentation,
the lactic acid bacteria ferment glucose mainly into
lactic acid; in heterofermentative lactic acid fermen-
tation, considerable levels of acetic acid are formed
in addition to lactic acid. The formation of lactic acid
and acetic acid during lactic acid fermentation can
and must be controlled, as the ratio of lactic acid to
acetic acid is quite important for optimal bread qual-
ity. Sourdoughs with a high lactic acid content are
used mainly for rye and mixed rye breads, while
sourdoughs with a high acetic acid content are ideally
suited for mixed wheat bread (Seibel and Brümmer
1991). One-, two-, and three-stage sourdough pro-
cesses are used (Meuser et al. 1994, Seibel and
Brümmer 1991). These processes require different
fermentation times, dough temperatures, and water
to flour ratios, and the resulting doughs have differ-
ent lactic acid to acetic acid ratios (Seibel and
Brümmer 1991). Depending on the proportion of rye
flour in the sourdough, various degrees of acidity are
required (Seibel and Brümmer 1991).
There are different reasons for using sourdough.
Acid conditions have a positive influence on the
swelling of rye flour constituents and control the en-
zyme activity in the dough, thereby preventing early
staling (Meuser et al. 1994, Seibel and Brümmer
1991). Rye flours with high enzyme activity require
a higher degree of acidification than flours with less
enzyme activity (Meuser et al. 1994). Bread sensory
properties, such as taste and aroma, can be improved
by optimal use of sourdough (Heiniö et al. 2003a,
Meuser et al. 1994, Seibel and Brümmer 1991). It
contributes to aroma in the bread due to the produc-
tion of acids, alcohols, and other volatile com-
pounds (Heiniö et al. 2003a, Poutanen 1997). Sour-
dough bread has good crumb characteristics (Seibel
and Brümmer 1991) and nutritional properties (Kar-
iluoto et al. 2004, Meuser et al. 1994, Poutanen
1997). Acidification of rye dough also protects