8. Optimizing Bread Rye Quality
for the Market
On the basis of the work of Drews (1971a, b) on the introduction of a
certain buffer for swelling curves, the Rye Viscosity Test (RVT) was developed.
The test makes it possible to obtain some important additional information in
about 30 to 45 min, a time that can usually be spared when rye is taken in, for
example by a mill. Because of the small sample quantities it requires, the RVT
can also be carried out by breeders as a selection criterion. The RVT is
currently undergoing practical trials, and over 100 samples have already shown
a certain correlation with baked volume. At the same time it has yielded
further proof that some lots with higher Falling Numbers may have good
inflation potential. In the past, only the Amando variety was known to have
this property. When compared with other varieties it always produced the
largest bread volume, independently of the site on which it was grown and its
Falling Numbers and Amylogram values (Fig. 96).
 |
| Fig. 96: Volume yields (rye/sour dough baking tests) of flours from
the rye variety Amando compared with flour from other varieties (mineral
content approx. 1% of dry weight; 1998 harvest) |
Because of the baking results obtained over the past decades, the
author considered it necessary to modify the current practice of assessing rye
solely according to the criteria of the BSA's descriptive list of varieties,
with steadily increasing results for 1000-grain weight, crude protein, Falling
Numbers and Amylogram values. More and more, rye lots are being recommended
whose high rheological Falling Number and Amylogram values are outside the
optimum range for good rye bread quality. One way of achieving a more accurate
prediction of bread quality is to carry out a standard baking test and determine
dough yield, the degree of leavening, the volume of the bread and the
elasticity of the crumb as quality criteria.
9. Current Rye Research and Processing
Properties
Compared with other cereals, rye has only brief secondary dormancy. So
under unfavourable weather conditions germination may start again, even in the
blade, soon after the morphological ripening of the grains. If germination is
visible it is known as visible sprouting. To the extent that they can be
detected analytically, the preliminary stages of germination are described as
latent sprouting.
Such germination leads to increased enzyme activity, which in turn
results in the breakdown of components of the cell walls and also stored
substances. As sprout-damaged rye is considered unsuitable for bread-baking,
this presented a challenge to breeders. In the past, α-amylase activity was
generally measured as a selection criterion; now the assessment is almost
always made on the basis of the Falling Number.
In rye research and analysis the pentosan complex used to be given
greater attention than the structure of the starch. But the following starch
ratios are considered relatively constant. At the time of ripening, the cereal
starch consists of about 25% amylose and 75% amylopectin. The starch grains can
be divided into two types: larger, lentil-shaped bodies with a diameter of
about 40 mm – "A-types" – and smaller, more spherical
"B-types" with an average diameter of about 10 mm. Besides these
there is a fluctuating but nevertheless appreciable percentage of medium-sized
starch grains. The exact ratio of A to B types of starch grains in rye is not
known. Whereas about 90% of the starch grains in wheat are of the B type, the
percentage of these smaller grains is thought to be somewhat smaller in rye. This
may have significance for resistance to sprouting, since the smaller B starch
grains and also the medium-sized types are more readily attacked by amylases
because of their larger specific surface area. But in spite of their larger
number, the percentage of smaller starch grains in the overall mass is fairly
small in terms of volume and weight. Dreisörner (2002) also found a
considerable proportion of medium-sized starch grains that increases with
breeding.
The starch is broken down by hydrolases, mainly through the combined
activity of the α- and ß-amylases in the cereal grains. When the grain is
stored in the field, especially, α-amylases from moulds and bacteria on the
ears and grains may have this effect. In particular the dextrins formed by
α-amylase may then be exposed to further attack by ß-amylase or
amyloglucosidase.
The α-amylase newly formed during germination seems to be an important
factor influencing processing quality. Its concentration increases during
ripening and reaches the highest values if latent or visible sprouting occurs.
A further breakdown is possible during gelatinization of the rye starch in the
baking process, in the presence of sufficient water, high temperatures and a pH
that is not too low.
There is an increase in temperature even when the grain is dried, but
little moisture is present. Such tempering has also been found to reduce the
tendency to gelatinize. This means that the water content of the grains is
extremely important for the activity of the enzymes. Their effect seems to be
greatest at a grain moisture of 30 - 40% and is largely prevented at values
below 20%.
Determination of α-amylase is a complicated matter. It is measured
with a large excess of water and often with the addition of a foreign
substrate, e.g. coloured starch. So determination of enzyme activity is even
farther removed from the conditions of bread-making than the Falling Number or
Amylogram method. However, the effect of the enzymes during processing is more
important than the enzyme activity that exists in absolute terms.
The grains contain a total of about 7 - 10% pentosans. Like proteins,
they are one of the swelling substances of the rye, but unlike protein they are
not considered to be energy reserves. The insoluble pentosans are a component of
the cell walls. The ratio of the soluble pentosans (part of the content of the
cell) to the insoluble pentosans (constituents of the cell walls) has yet to be
determined. Larger percentages of insoluble pentosans are indicated by
increasing Falling Numbers of the flour, whereas larger percentages of soluble
pentosans seem to affect the peak values of the Amylogram but not the Falling
Numbers. The pentosans are readily attacked even at dough temperatures, so it
makes sense from the technical point of view to determine them. The behaviour
of the swelling substances of the rye during processing (e.g. viscosity of the
dough) is therefore determined by the pentosan and protein content and its
susceptibility to attack.
 |
| Fig. 97: Flow diagram of the Rye Viscosity Test |
Certainly an adequate reduction of viscosity has to be ensured in
order to achieve the required attributes of the bread. This complex will
doubtless become an important feature of technical rye research in the near
future, especially as some rye varieties seem to react more sensitively than
others to an overdose of water or cause greater softening of the dough in spite of high Falling
Numbers, as swelling curves and the new Rye Viscosity Test (Brümmer, 2002) show
(Fig. 97). Successful breeding in respect of yield and the reliability of the
yield is making rye more attractive again as a crop. Both of these factors and
also resistance to sprouting still depend chiefly on the weather, harvesting
techniques and post-harvest treatment and less on the properties of a
particular rye variety. In Germany, the
characteristics of different rye varieties were only apparent under very
uniform weather conditions. But in spite of fluctuations, years of quality
testing of milled rye products have revealed certain trends (Fig. 98).
 |
Fig. 98: Comparison of the analytical data for the German rye harvests
of the years 1983 – 2002 (rye flour types 997/1150)
|
The past few years, including the harvest of 2001, have almost made us
forget that rye is still susceptible to sprouting. Although the rye of 1993 and
2002 broke down rather more readily, the commercial flours were drier when
baked than ideal bread flours. This raises the question as to how much
"sprouting" is necessary for baking bread and other, smaller products
containing rye.
To answer this question, bakers have mainly considered the Amylogram
and the baking test, complemented by the Falling Number, maltose content and
swelling curve. The Falling Number is a quick determination method, but it is
subject to greater fluctuations in respect of suitability for processing than
the peak Amylogram temperature, for example.
 |
Fig. 99: Processing quality and results of indirect methods for rye:
rye Amylogram – peak temperatures and Falling Numbers and expected suitability
of the milled products for baking
|
Fig. 99 is an attempt to correlate the results of indirect methods
with good bread quality. The "quality window" in the centre of the
diagram shows the analytical ranges especially recommended for making bread and
other small products containing rye. Outside this frame the uses of other ryes
that break down more readily or less easily during baking are shown. Ryes that
break down very readily should only be used for coarse meal. Milled products
that reach into the dry baking range for flours of the types 997/1150 may be
regarded as particularly suitable for fine whole meal or wholemeal flour. Of
course lots of this kind can also be used for making special baked products
such as crispbread or to improve lots of rye whose substrate is too susceptible
to attack or which show too much enzyme activity (mixed rye).
At present, millers are still very hesitant to grind rye with low
Falling Numbers and Amylogram values in the usual way – probably a result of
bakers' fears. But some bulk buyers have now recognized the opportunities
offered by such rye properties for enhancing the quality of their bread.
إرسال تعليق