ALPINE
Increased Water Absorption
of Wheat Flours
through Attrition Grinding
Increased Water Absorption of Wheat Flours through Attrition Grinding
A good water absorption of flours is a
desire which may exist since the invention of dough making and baking. This
is due to the manifold advantages the
bakers could ascribe to an increased
water content of dough and thereby of
bread.
Advantages of Increased Water Absorption

Dry Dough Surface

Good Machineability of Dough

Increased Bread Yield

Improved Fermentation

Better Taste
Percentage Points Water Absorption
Cereal research could establish that
 Softer Crumb
water binding of wheat flours is to be
 Delayed Staling
attributed to protein, soluble pentosans
 Avoidance of Water Binding Additives
and damaged starch. To increase the
 Longer Keepability
amount of the very effective soluble
pentosans no measure is known. The
protein content can be influenced by breeding and agricultural measures (e.g. application of
fertilizers). But, when the wheat has already entered the mill, damaged starch is the only component, which can be increased by
Water Absorption of Wheat Flours
milling procedures. Many efforts were
made to achieve a higher water
absorption of flour through damaging
30
starch than was given with usual
25
equipment, but, with limited success
20
only. Different investigators could not
overcome a threshold of additional 10
15
percentage points Farinogram Water
10
Absorption though using aggressive
5
milling or crushing devices. As, at
least up to the aforementioned
0
Sol.
Damaged
increase, in normal cases a high
Protein
Pentosan
Starch
content of damaged starch via the
improved water absorption is advantageous for baking and the bread properties, it seems to be
only fair to use the term “activated starch” instead of “damaged starch”.
In the given limits the influence of activated (damaged) starch on the baking results were
exactly examined by Farrand. He found out that the gluten matrix formed out of wheat protein
and water is able to integrate a certain volume of starch. After activation starch has taken up a
remarkable amount of water thereby
Possible Measures for Influencing Water Binding of Wheat Flours
expanding its volume. As long as the
Protein
Soluble
Damaged
starch with the thus increased volume
Pentosans
Starch
can be still integrated in the gluten
Breeding
x
(x)
matrix the baking effect is advantaAgriculture
x
?
geous. Once the gluten matrix cannot
Milling
?
xx
longer integrate and cover the swollen
starch granules the given ruptures in the
dough cells cause a loss of carbon dioxide ex fermentation, this loss being responsible for a
decrease in bread volume. Thereby the benefit of starch activation is revealed to be dependent
on the protein- respectively gluten-content of flour. For the gluten quality as well as the enzy1
matic status of the flours play an important role in this relation, the Farrand model unfortunately cannot be used for exact calculations.
Good quality “hard” wheats
show obviously a better response to milling efforts with
respect to the content of activated starch. It is assumed that a
firmer structure of the starch
granules allows a more effective
crushing, whereas the more
elastic starch granules ex
“weak” wheat varieties can
better overcome the milling
stress without being activated.
Another theory ascribes the
better activating properties of
hard wheat starch to the strongly
adhesive protein on the surface
of the starch granules which is
missing on weak wheat starch.
Water Absorption
Starch Activation
As a result the efficiency of a milling process is not only depending on the equipment but on
the wheat quality, too. A really accurate prediction of the activating performance therefore
cannot be given, for the quality
Influence of Wheat Quality on Efficiency of Starch Activation
of a flour made of a commercial
wheat is normally not exactly
known. In Germany the poorer
E
wheats w.r.t. baking quality are
characterised as “C” and “B”
A
whereas the better wheats are
rated as “A” and “E” (Elite).
B
There are qualitative indications
but no quantitative data in how
C
far this rating influences the
Test Flour
resulting content of activated
Wheat Quality (German Classification)
starch. Nevertheless an influence as given in the accessory
graph has to be expected. The reference (test-) flour used for the below described examinations is a medium quality one.
That intensity of the milling procedure correlates positive with starch activation and hence
water absorption of flour can easily be understood. Roller mills and pin mills were extensively
tested to which extent starch activation could be achieved. The results exhibited for both kind
of mills a limit of additional 10 per cent points Farinogram Water Absorption. The particular
reasons shall here not be discussed in depth. Some investigators found strong indications that
ball milling of flour could be quite more effective in this regard. As the research was not followed up it can well be assumed that some restrictions caused by the used small scale equipment and the batch process could not be eliminated.
2
Having negotiated these first
findings, the engineers and scientists of Hosokawa Alpine reflected upon the basics of the
different milling processes. Pin
milling seemed not to be a
viable procedure to activate
starch. The strong impact
applied for a split second causes
an elastic deformation and in a
very short time the deformed
starch granule recovers its
original shape. Starch activation
but was found to be due to an
irreversible deformation of the
granule, combined with the
formation of fine fissures
allowing water to enter and
swell the granules.
Comparison of Milling Principles
Cylinder
Ball
Pin
Stress, Shear
Stress, Punch
Impact
Roller milling performed with a pair of cylinders rotating with different speed offers better
measures to activate starch. UnforWorking Area of Cylinder and Ball
tunately the necessary energy dissipation
takes place in a very restricted area, i.e.
the cylinder surface near the milling gap.
The investigators found, what was to be
expected: strong energy input resulted in
40 
strongly increasing temperatures, thereby
damaging flour protein, creating flaking
effects or even causing fire hazards.
d
Cylinder:
=
300 mm; d = 4.90 mm
Ball:
=
5 mm; d = 0.63 mm
The ball milling (attrition) procedure is
based on similar principles as roller milling. The space between cylinders or
balls respectively in which starch
granules possibly can be influenced and
energy input may occur has a width from
0 up to 40. A calculation based on this
assumption shows that milling balls (better:
pearls) do offer not only an obviously
higher specific surface but an energy
dissipation area which is several orders of
magnitude larger than that of cylinders.
This allows a high specific energy input
distributed on thousands and thousands
contact places, each locally separated from
the other. Overheating problems do not
arise at all; if necessary, the cycled balls
(pearls) can be cooled down with quite
simple methods, e.g. air cooling.
3
Backbone of the designed attrition
plant is the well-tried Hosokawa
Hosokawa Alpine Ball Mill ATR
Alpine ATR ball mill. The milling
1
2
pearls are passed through the milling
chamber together with the flour to be
milled. The pearls are then separated
in a sieve and, in a cycle procedure,
Legend:
transported back to the feeder of the
1 Controlled Drive
mill. This machine was in a first step
2 Right Angle Gear
3
combined with appropriate equipment
3 Stirring Axle
4 Stirring Rods
to form a plant for the attrition
5 Controlled Conveyor
treatment of wheat flour in which the
flour is milled in a cycle procedure.
4
The created fine fraction is then separated by a classifying unit (Hosokawa
Alpine ATS). The thus removed
material is replaced by freshly
5
introduced unground flour. As it was
assumed that starch activation
preferably was achieved with the fine particles these are effectively extracted out of the
process. It has to be checked, however, whether the assumed higher starch activation of the
Circular Process
3
2
7
8
4
1
9
5
6
10
Legend:
1 Elevator
2 Ball Mill
3 Feeding Bin
4 Vibrating Sieve
5 Collector for
Milling Pearls
6 Collecting Bin
7 Classifying Unit
8 Filter Separator
9 Aspiration
10 Outlet
fine flour fraction is really given. For this purpose an analytical investigation was made.
Evaluating the analytical data one has to consider that the process starts unbalanced as in the
beginning the separated fine material has an increased protein content. The balance is given,
when the separated flour has exactly the same protein content as the fed flour. In this status
the cycled flour has a remarkable lower protein content. The set of obtained analytical data
showed firstly that the balance of the process was given after 180 minutes. Furthermore it
4
Parameters of Original Flour, Delivered Flour and Circulated Flour
in Balanced State of Process
could be derived that the
cycled flour - despite of its
coarser particle size - exhibited nearly the same starch
activation and Farinogram
Water Absorption.
Protein
i. D.M. (%)
48421-Original F.
48421/9 180'-Fine
FarinogramWA (%)
12.7
7.2
59.6
9.4
8.8
78.0
12.5
8.8
79.8
48421/9 180'-Coarse
The conclusion is very pleasing: the quite complicated
arrangement can be simplified.
Act. Starch
i. D.M. (%)
The relevant pictures unveil that, compared with the circular process, the straight through
process can work without a remarkable number of expensive components.
Straight Through Process
2
3
Legend
1
2
3
4
5
6
7
4
1
7
6
5
Farinogram Water Absorption vs. Energy Input
95
90
85
Farinogram-WA in %
The straight through process
delivers an excellent correlation
between specific energy input and
water absorption. In the pilot plant
an increase of approx. 30 percentage points Farinogram Water
Absorption could be achieved.
Higher values would have needed
a stronger motor power. Based on
these results in a commercial plant
water absorption values of additional 40 percentage points will be
realised.
Elevator
Ball Mill
Feeding Bin
Vibrating Sieve
Collector for Pearls
Outlet
Aspiration
R = 0.965
80
75
70
65
60
55
50
0
20
40
60
80
100
120
140
160
180
Specific Energy Input in kWh/t
5
200
The graph shown above is altered
now. The additional water uptake can
be ascribed to the extended amount of
activated (damaged) starch.
Farinogram-Units
The course of the Farinogram is,
compared with the Farinogram resulting from the original flour, not
remarkably altered. Although nearly
30 percentage points more water was
taken up the concerning Farinogram
does not indicate any slackening of
the dough what can be observed
sometimes if flours are too finely
milled. The quite normal appearance of the Farinogram, however, should not mislead to the
expectation that a norFarinograms of Wheat Flour before and after Attrition Grinding
mal baking result can
be achieved with a
dough having this
600
highly enhanced water
WA 59.8
500
content.
In
this
400
context the afore300
mentioned has to be
WA
88.1%
pointed out: starch
200
activation, expressed
100
as increased water ab0
2
4
6
8
10
12
14
16
18
20
sorption, and gluten
content has to be in an
Time in Minutes
optimum balance.
Raster Electron Microscopy (SEM) examination can help to understand how the
applied mechanical attack changes the
structure of the starch granule thereby activating it. Normally the round starch granules are quite stable and elastic. After
impact they easily recover their original
shape. The first magnification shows, however, that after attrition grinding, they have
flattened areas, “poles”, and a trend towards
a polyedric shape may be detected.
SEM-Photo of Wheat Flour
after Attrition Grinding I
10 
That may be not sufficient to explain the
dramatically changed properties of the
starch granules w. r. t. their water absorbing
capability. A further, greater SEM-magnification reveals the reason: a lot of small
fissures created by the specific influence of attrition grinding allows the water molecules to
6
easily enter and to penetrate into the
starch granule. The water absorbed in
this way shows a very strong bond to
the starch; as already mentioned a
release during dough kneading cannot
be detected.
SEM-Photo of Wheat Flour
after Attrition Grinding II
Viscosity in cp
The temperature of the flour leaving
the activating process does not exceed
1
40°C. This is not at all sufficient to
inactivate the enzymes present in the
flour. Consequently the Falling Number is not affected by the process. The
same applies for the position of the
viscogram-maximum the temperature
of which does not shift remarkably.
Of course it was expected that the
level of the maximum viscosity
decreased remarkably as it is shown in
the accessory graph. Together with
water the amylolytic enzymes can penetrate into the granules and effectively attack the
amylose- and amylopectin-chains thereby breaking down the components developing the
viscosity of a gelatinised flour slurry. As a second result the production of dextrins is strongly
intensified with a lot of advantages (and a few disadvantages of course) causing an improved
bread quality. So a very good
Rapid Visco Analyser Maximum vs. Energy Input
negative correlation is given
between the specific energy
700.0
input and the height of the
600.0
viscogram maximum.
500.0
As already was pointed out it
is most likely that the enhanced water absorption of
400.0
300.0
200.0
R = 0.943
95
100.0
90
0.0
20.0
40.0
60.0
85
80.0 100.0 120.0 140.0 160.0 180.0 200.0
Farinogram-WA in %
0.0
80
Attrition Grinding
Specific Energy Input in kWh/t
75
70
flours through attrition grinding is
65
generated by activation (damage)
of starch. Thus, the amount of
60
Original Flour
Pin Mill Grinding
damaged starch is rising with spe55
cific energy input. The correlation
50
between energy input and starch
0
20
40
60
80
100
120
140
160
180
Specific Energy Input in kWh/t
damage (measured acc. to ICC
Standard 164), however, is not
satisfying. This may be due to disturbing influences on the analytical procedure which could
not yet be tracked down.
7
200
The evidence, that attrition
treatment (ball milling) is a
method particularly useful for
increasing water absorption in
flour
(through
activating
starch) is given by a comparison between pin milling and
ball milling. Pin milling has an
influence on the water absorption of flour, too, but the
steepness of the correlation
straight line is remarkably
lower than with ball milling.
The integration of an attrition
plant for activation of flour
starch into a milling flow
sheet can be managed according to the millers needs. The two examples given are not an
exhausting survey.
Although
enhanced
water absorption is
doubtless a desirable
property of many wheat
flours, it must be justified by an economic
advantage for the usual
broad utilization in bakeries. Some tables in
this paper offer an instrument for an user to
check whether this is
the case for his particular purpose; some
exemplary calculations
are given. Nevertheless
it has to be mentioned
that very interesting
ATR: Prices and Figures
additional applications in the food production other than baking may exist. Flours
with high water binding capacity will be
e.g. useful as component in breading mixes
and as general substitute for thickeners. For
the resulting commercial benefit figures
cannot yet be given: firstly the applications
have to be realised by way of trials.
Cost Price (€)
250,000
Throughput (kg/h)
500
Production Days/a
300
8-Hr.-Shifts per Day
2
Production Hours/a
4,800
Production (t/a)
2,400
Energy/t (kWh)
190
Energy Cost (€/kWh)
Energy/a (kWh)
-.045
456,000
8
ATR: Production Costs/a
Depreciation 10 Years (€)
Interest 6% (€)
Energy Costs (€)
Working Costs 0,1 Man/d (€)
Cost of Repairs 2% (€)
Total Costs (€)
Costs (€ /t)
25,000
7,500
20,520
5,000
5,000
63,020
26
Cost Advantages through Attrition Ground Flour
€ /% kg
kg
€
€
kg
€
kg
€
kg
Flour T. 550
23.0
100.0
23.0
95.0
21.9
98.6
22.7
99.6
22.9
Attr. Gr. Flour T. 550
25.6
-
-
5.0
1.3
-
-
-
-
Pregelatinised Flour
55.0
-
-
-
-
1.4
0.8
-
-
150.0
-
-
-
-
-
-
0.4
0.6
-
60.0
-
62.0
-
62.0
-
62.0
-
160.0
23.0
162.0
23.2
162.0
23.5
162.0
23.5
Guar Gum
Water
Total Sum
Mat. Costs/1000 kg Dough
144
Difference/1000kg Dough
1.-
143
145
-
145
2.-
2.-
Raw Material Costs in €/t
"Sensoric" WA in %
In some cases mills fulfil the market demand for flours with higher water absorption with the
integration of high quality (Elite-) wheat in the fed wheat mix. As this kind of wheat is
remarkably more expensive (e.g. €/t 145.- instead of €/t 130.- for faq-wheat) a partly replacement of E-wheat by attriCosts for Increased WA: E-Wheat / ATR-Treatment
tion ground flour can help
350
to remarkably reduce the
70
resulting
costs
while
300
maintaining the property
60
250
of high water absorption.
50
200
One has to confess that
40
150
this will not work in cases
60
62
62
162.5
168.0
165.2
30
where
the
improved
100
baking power of the flour
20
50
with high E-wheat portion
10
0
is necessary. The term
0
“sensoric”
WA
was
R
R
q
q
E
E
chosen for the measure is
fa
fa
AT
AT
+
+
+
+
q
q
a
a
E
E
f
f
+
+
rather based on the
q
q
fa
fa
practical findings of a
WA
Costs
baking expert than on the
faq = fair average quality
result of a Farinograph
examination.
9