wheatstruc, nv, c and m

 Historic documents confirm that wheat is the earliest field
crop used for human food processing .
 It also became the leading grain used for human
consumption due to its nutritive profile and relatively easy
harvesting, storing, transportation, and processing, as
compared to other grains.
 The earliest varieties, grown 12,000-17,000 years ego in the
Near East, were Triticum monococcum (einkorn) and
Triticum dicoccum (emmer).
 Continued breeding resulted in the development of new
varieties around the world that often became adapted to
areas previously unsuited for the cultivation of wheat.

Prepared by Hab2 S. 1

 The main wheat varieties grown today are Triticum
aestivum, subspecies vulgare, which is a hexaploid with six
groups of seven chromosomes in each group.
 This species includes hard red winter, hard red spring,
soft red winter, and white wheats.
 Another wheat durum is a tetraploid, containing four
groups of seven chromosomes totaling 28 chromosomes.
 The botanical name of durum wheat is Triticum durum.
 A limited area is planted with the soft white wheat variety
of Triticum aestivum, subspecies compactum, commonly
known as club wheat.
 Currently about 4000 different wheat varieties are grown
around the world.


 Data related to the morphology of the wheat kernel and

proximate analyses vary in different research reports.
 This variability is likely due to the different types and growing

conditions of wheats analyzed.
 In general, there are about 30,000 cells in a wheat kernel, and

their content varies significantly depending on their location
in the kernel .
 The morphology of the wheat kernel is unique and as such

creates technical (milling) challenges in separating the
endosperm and the germ from the outer fibrous layers,
commonly named the ''bran."

 The presence of the crease (about 25% of the kernel

surface), which extends almost to the center of the wheat
kernel, requires special consideration in grinding.
 The wheat germ (about 24% of the kernel weight) is

located on the dorsal side.
 The wheat germ parts are the embryo, with rudimentary

roots and shoots, and the scutulum, which is a transport
organ of nutrition to the embryo during sprouting.


 The wheat kernel outer botanical coats (about 78% of the

kernel weight) consist of several distinct cellulose-rich
layers.
 The outermost layer, the pericarp (fruit coat), is made up

of the outer pericarp, which includes the outer epidermis,
hypodermis, thin-walled cells, and the inner pericarp,
which includes intermediate-size cells, cross layers, and
tube cells (inner epidermis


 The inner layers are the seed coat (testa) and nucellar

epidermis (hyaline layer) .
 Between the nucellar epidermis and the starchy endosperm we

find the aleurone layer, having high soluble protein and mineral
contents.
 The aleurone layer constitutes about 58% of the wheat kernel.

 This layer is botanically similar to the endosperm, but it is

difficult to separate from the bran by conventional milling
techniques.
 Depending on the kind of wheat, the thickness of the aleurone

layer varies.

 Mechanical damage or hydrolysis with cellulase of the

aleurone thick cell wall allows access to proteins within
the aleurone layer .
 Although nutritious, incorporation of a fraction with a

large percentage of aleurone layer adversely affects the
baking quality of flour .
 The endosperm of the kernel was also shown to follow a

gradient in ash, protein content, gluten characteristics,
and baking quality.


 Many wheat kinds and classes, available around the world,
vary in quality as a result of climate, irrigation, specific
variety characteristics, growing conditions, harvesting,
and handling.
 Presently, wheats are graded differently in exporting and
importing countries .
 In some countries the government is involved in setting
limits for contaminants in imported wheats.
 In others, mainly exporting countries like United States,
government officers inspect, according to official
standards, all exported wheat; domestically traded wheat
is inspected upon request only.
 The current grading system covers eight classes of wheat:
 durum, hard red spring, hard red winter, soft red winter,
hard white, soft white, unclassed, and mixed wheat.
 Durum, hard red spring, and white wheat are further
divided into subclasses.

 According to the U.S. standards for wheat, the definitions
for the classes and subclasses are as follows:

 1. Durum wheat: all varieties of white (amber) durum
wheat.
 This class is divided into three subclasses:
 (1) hard amber durum wheat this subclass designates
durum wheat with 75% or more of hard and vitreous
kernels of amber color;

 (2) amber durum wheat this subclass is durum wheat with
60% or more but less than 75% hard and vitreous kernels
of amber color;
 (3) durum wheat durum wheat with less than 60% hard
vitreous kernels with amber color.

 2. Hard red spring wheat: all varieties of hard red spring

wheat.
 This class is divided into the following three subclasses:

 1 dark northern spring wheathard red spring wheat with

75% or more dark, hard, and vitreous kernels;
 2 northern spring wheathard red spring wheat with 25% or

more but less than 75% dark, hard, and vitreous kernels;
 3)red spring wheat hard red spring wheat with less than

25% dark, hard, and vitreous kernels.
 3. Hard red winter wheat: all varieties of hard red winter

wheat. There are no subclassesby Hab2 S. wheat class.
Prepared in this 11

 4. Soft red winter wheat: all varieties of soft red winter
wheat. There are no subclasses in this wheat class.
 5. Hard white wheat: all hard endosperm white wheat
varieties. There are no subclasses in this class.

 6. Soft white wheat: all soft endosperm white wheat
varieties.
 This class is divided into the following three subclasses:
 1 soft white wheat soft endosperm white wheat varieties that
contain not more than 10% of white club wheat
 2white club wheat soft endosperm white club wheat
containing not more than 10% of other soft white wheats

 3 western white wheatsoft white wheat containing more than
10% white club wheat and more than 10% other soft white
wheats.

 7. Unclassed wheat: any variety of wheat that is not
classified under other criteria provided in the wheat
standards
 There are no subclasses in this class.

 This class includes any wheat that is other than red or

white in color.
 8. Mixed wheat: any mixture of wheat that consists of less

than 90% of one class and more than 10% of one other
class or a combination of classes that meet the definition
of wheat.


 The value of wheat depends upon its milling and flour end

use quality.
 This can be accurately determined through actual milling

and baking tests.
 The miller has to assess wheat quality and evaluate its

suitability to produce, individually or in a blend, final flour
specifications.
 In addition, the miller has to determine the expected

wheat-processing performance in the mill, the resulting
flour extraction, and other qualities such as color, particle
size, and starch damage. Prepared by Hab2 S. 15

 Flour extraction is the proportion of the wheat recovered as

flour during milling.
 The following are tests of importance to the miller for

evaluating wheats and flours:
 experimental milling, physical, chemical, physical-chemical,

dough rheology, and the baking test. Wheat and flour testing
can follow different official methods such as those of the
American Association of Cereal Chemists (AACC), the
International Association of Cereal Chemists (ICC), or the
Association of Official Analytical Chemists (AOAC).

 1. Test weight: quality test which is basically a rough
measure of density of grain in terms of weight per volume,
i.e., the weight (lb.) per volume bushel (Winchester bushel
in U.S.; Imperial in Canada).
 The hectoliter weight (hL), indicating the weight in
kg/hL (100 L), is used in the metric system countries.
 No uniform conversion factors between test weight and
hL weight values are possible due to differences in kernel
shape, size, and procedures for determination of these
values.
 2. Thousand kernel weight (TKW): a quality test to
determine the potential milling value of wheat.
 Weight of 1000 kernels gives an indication of kernel
density and its consequent flour yield.
 The advantage of TKW is that the weight can be expressed
on a desired-moisture basis.

 3. Kernel size distribution: the size distribution of

kernels in a wheat sample can be determined using a stack
of sieves. The ''theoretical flour yield" can be determined
by the total value of multiplying the percentage above
each sieve by a factor .
 The factors can be calculated using multiple regression

analysis for a mill, based on a database in which
percentages of wheat sizes are the independent variables
and the actual flour yields are the dependent variables .


 4. Kernel hardness: a relative term, which is related to the
disintegration of the endosperm during its separation from
bran and germ.
 Currently, hardness values are determined by near-infrared
refraction (NIR) or mechanical crushing instruments such as
the single kernel characterization system (SKCS).
 They are used to identify variation of wheat characteristics in
the trading system as well as indicate processing characteristics
 5. Assessment of the milling quality of wheat is performed
using an experimental unit using a sample of about 1000-1500
g.
 Experimental milling can give a preliminary indication whether
a wheat alone or in a mix of wheats complies with a required
quality.
 An experimental mill should be differentiated from a
laboratory mill that is a milling unit with a fixed setting, where
all wheat samples are treated in the same manner during

 5. Assessment of the milling quality of wheat is performed
using an experimental unit using a sample of about 1000-1500
g.
 Experimental milling can give a preliminary indication
whether a wheat alone or in a mix of wheats complies with a
required quality.
 An experimental mill should be differentiated from a
laboratory mill that is a milling unit with a fixed setting, where
all wheat samples are treated in the same manner during
milling.

 Flour samples produced with laboratory mills in a relatively
short time can be used for further testing but do not provide
information on the wheat-milling properties.

 Official methods explain the procedures for using
experimental mills and should be followed rigidly, preferably
by the same operator . Prepared by Hab2 S. 20

 Improved experimental mills are fitted with technical
parameters of the commercial mill where the wheat is expected
to be processed.
 Accurate sampling, tempering, and controlled environment in

the facility and uniform practices ensure reproducibility and
confidence in the results.
 Flours from experimental milling procedures could be used for

further rheological and baking tests.
 6. Other physical and chemical evaluation tests performed

in the mill laboratory include those for moisture, protein,
ash, fatty acids, amylase activity, Falling Number, and
gluten quantity and quality. by Hab2 S.
Prepared 21

 It is important to preserve the quality and economic value

of wheat as it moves from the field into storage at the
processing mill.
 If not properly stored, insects, moisture damage, or other

conditions may cause losses. Moisture and temperature are
two main factors that influence the development of grain
molds and insects in stored wheat.
 In some areas of the world, where wheat is harvested at a

high moisture content, wheat should be carefully dried to a
moisture below 12.5%, a level regarded as safe for storage.

B. Blending
 Usually a mill is designed for milling wheat of a certain class

and physical characteristics.
 However, a mill designed for one class of wheat (e.g., hard or

soft) does not ensure uniformity of end-product quality.
 Wheat arriving at the mill usually varies in quality and

requires blending to deliver a "wheat mix" of uniform
qualities.


 Wheat blending is the initial step in providing bakers with

a uniform flour.
 Accordingly, mills prepare "wheat mixes" of certain protein

levels or other quality characteristics.
 There are different methods of blending.

 Some millers blend wheats directly in storage bins, others

before grinding.
 Wheat blending just before the milling process is mainly

applied when the components of the "wheat mix" differ in
endosperm hardness and require adjustments of moisture
levels and tempering times prior to milling.

C. Cleaning
 Intensive cleaning of the wheat before milling ensures that
bacteria, mold, undesired seeds, infested kernels,
shrunken and broken kernels, and other foreign materials do
not contaminate the mill products or damage the equipment.
 Separation in the mill cleaning house is based on the following
differences between whole sound wheat kernels.
D. Conditioning
 Conditioning, a process that adjusts the moisture level of wheat
before milling, achieves a mellow endosperm and tough bran.
 Bran that absorbs proper amounts of moisture becomes elastic
and will not splinter during grinding to contaminate the flour
with fine particles.
 Mellow endosperm breaks off the bran during grinding, and less
power is required to reduce large pure particles to flour.


 On the other hand, an excessive moisture level softens the
wheat endosperm to a degree where it does not have the
resistance to break down to sharp particles that is
important for efficient sieving and separation from the
bran.
 Another objective of wheat conditioning is to equalize the
hardness of the different kernels in the wheat mix before
processing.
 If the moisture content and hardness of wheat lots in a
mix are significantly different, they might be treated
separately during the conditioning process.
 Different methods could be used to condition the wheat
before milling.
 Heating the wheat, application of warm water, application
of live steam, or just intensive mixing of wheat and water
are some of the methods used to increase the amount and
rate of water penetration into the kernel.

 Moisture pick-up by wheat capillary action increases slightly and

linearly with increasing water temperature .
 The increase from the initial temperature of 26.7°C is approximately

2% at 30°C and 4% at 90°C for each variety of wheat.
 Excessive heat (above 65°C) results in gelatinization of starch and

protein denaturation.
 The current method most frequently used is termed ''tempering."

 According to this procedure, a calculated amount of water is added

to the wheat, which is then intensively mixed in a continuous mixer
in order to maximize a uniform dispersion of the water on all wheat
kernels.


 Wheat flour milling is a process that consists of controlled
breaking, reduction, and separation.
 The objective during milling is to separate the branny cover
and germ of the wheat kernel from the endosperm.
 Breaking of the wheat kernel is affected by corrugated cast
steel rolls that gradually separate the endosperm, bran, and
germ.
 Reduction of relatively pure endosperm to particles smaller
than 180 mm is achieved by using smooth rolls.
 Segregation between the kernel parts occurs in sifters and
purifiers.
 In sifters, sieves separate particles of different size.
 In purifiers with sieves and air, differences in size, specific
gravity, and shape of particles are used to separate particles
of pure endosperm and those which include different ratios
of bran and endosperm.

 None of the kernel fractions coming out of the mill are
completely pure, and each contains some parts of the others.
 The level of purity of each product at the end of the mill is one
of the measures of mill efficiency.
 Flour extraction in the mill is measured as percentage of flour

produced based on a quantity of wheat that is either dirty, dry,
clean, or cleaned and tempered.
 The basis used for calculation of the extraction rate should be

stated with the results.
 Another measure is the gain/loss or the difference between the

wheat arriving in the mill and the total weight of products
shipped out.


 There should be a gain of total product weight after the
milling process as a result of the difference between the
moisture content of the wheat arriving at the mill and the
cumulative moisture content of all final products.

 The flour-milling process consists of numerous stages that can
be divided into the following sub-processes: breaking,
grading, purification, sizings, reduction, mill feed
handling, germ recovery, and flour dressing.

 Materials at different stages of the milling process differ in
quality or in the ratio of bran to endosperm and particle
size.
 The efficiency of gradual separation between the endosperm,
bran, and germ is directly related to the length and the
number of stages in the process. by Hab2 S.
Prepared 30

 Segregation of the intermediate materials to different

grinding stages is based on their size and the amount of
undesirable bran and germ particles.
 In an optimal system each of the materials would be

treated individually.
 However, grinding rolls, sifters, and purifiers are
manufactured to standard sizes, and this causes mill
designers to compromise on the number of separations in
respect to quality and quantity of the intermediate
materials.


 Accordingly, the extent to which intermediate materials are

subdivided in the mill is a function of the mill capacity.
 If the mill capacity is too small, different stages would be

underloaded with standard size equipment, and in this case
products that are only slightly different should be combined.
 The initial grinding stages in the milling process are named

"breaks."
 The breaks are used in the grinding steps of the milling

process to separate the bran, germ, and endosperm from each
other.

 The success or failure is measured in the level of

achieving, as efficiently as possible, complete separation
between the kernel parts.
 In the conventional milling of hard and durum wheats, the

objective is to produce minimal amounts of flour in the
breaks but a maximum of clean endosperm chunks.
 However, with soft wheat, because of the softer, less dense

endosperm, the percentage of flour extracted from the
breaks in conventional milling is higher than that from
hard and durum wheats.

 One study reported that hard, soft, and durum wheats
produced on the first three breaks are 49.8, 44.7, and 77.4
and 5.7, 10.5, and 2.0% of sizings and flour, respectively.
 Starting with the first break, the objective is to open the

kernel.
 The shape and depth of the first break roll corrugations

should be selected to fit the size of the kernels.
 Optimum results in the first break are achieved if the

kernels are fed to the gap between the rolls horizontally,
held by the corrugation of the slow-moving roll, and
opened exactly at the crease by the fast-moving roll.

 Optimum for the second break rolls and the subsequent

breaks is feeding the material (endosperm attached to a flake
of bran) directly to a precisely adjusted gap where with the
right pressure the fast-moving roll scrapes the endosperm
from the bran.
 As the bran flakes get smaller toward the final breaking stages

and the endosperm layer attached to it becomes thinner,
gradually smaller corrugations are used (or a larger number of
corrugations per inch of roll surface).


 Optimally conditioned wheat and the right corrugations,

pressure, and differential minimize splitting of the bran to
particles of a size that can be sieved through with the
flour.
 Good results in conventional milling are obtained when

most of the endosperm free bran consists of large flakes.
 Conventionally with a longer break system, up to six

stages in hard wheat and seven in durum wheat mills, it is
possible to grind the material fed to the rolls in a less
severe manner.
 Roll surfaces should be maintained in good condition to36
Prepared by Hab2 S.

 Depending on the quality of the steel and the type of
milling technology used, corrugated rolls should be
refurbished every 36 months of milling.

 Other factors that influence the need for refurbishing are
roll surface allocation, feed rate per unit, severity of
grinding, wheat hardness, and presence of stones or other
impurities in wheat.
 Recent advances in metallurgy that allow casting of harder
outer surfaces for corrugated rolls extend the time
between refurbishing up to 8 months.

 Even when the mix in the mill is changed drastically in
wheat size and kernels are smaller or larger than normal,
usually mills will continue using the existing corrugations,
keeping many exiting variablesbyunaltered.
Prepared Hab2 S. 37

 Generally, the gap between the rolls will be adjusted

intuitively by the miller based on his or her experience.
 A few studies were conducted to evaluate the first roll

action and the different parameters that could effect
conventional milling of different kinds of wheat.
 Grinding of soft and hard wheats on a set of rolls at

different rotating speeds indicated that better separation
between bran and endosperm occurred on the first break
with a lower speed and smaller diameter.
 Wheat moisture is another important factor that affects

the grinding process for common and durum wheat

1. Sieving
 In the sifter, particles of the grounded material are separated
according to size.

 Sifters are available in two, four, six, and eight sections.
 Modern sifters are more sanitary than those used in the past,
which often were a source of infestation.
 The sieves in a sifter section are divided into groups.
 At the top of the section, there are usually coarser sieves
separating the larger material that flows out of the sifter
through a side channel.

 The material passing through the sieve is either transferred
out of the machine or directed down to finer-aperture sieves
for a further separation. Prepared by Hab2 S. 39

 Below each sieve, a backwire is attached to the frame on
which hard rubber balls, plastic elements, or cotton pads
bounce to keep the sieve clean.

 ''Throughs," a stream passing through the upper sieves in a
break stage sifter, is a mixture of flour and chunks of
endosperm to which often some bran is also attached.

 While the "overs" of the top sieves are transferred to the
next break for additional scraping of endosperm, the
mixture of the throughs is segregated, based on particle size
differences on lower sieve groups in the section.

 This is evident from a schematic view of a first break sifter
section where six materials that differ in quality and size
flow out.

 Graders are sifter sections used to handle mainly materials directed

from the breaks.
 A blend of medium-sized and fine sizings as well as middlings is

directed to the graders.
 Materials from primary breaks are directed to the first grader.

 Materials from secondary breaks (e.g., the third or fourth) are

directed to second or third graders.
 The main objective of the grader is to remove the remaining flour

from the middlings and to separate the granular material to narrow
particle size ranges for better efficiency in the purifiers.

 At the head end of the milling system granular intermediate
materials of the same size range are directed to machines
called purifiers.
 The different size groups differ also in the amount of pure
endosperm, bran, and such particles of endosperm to which
bran is still attached.
 The more similar the particles are in size, the more effective is
the purifier performance.
 The purifier's main purpose is to separate particles into
fractions of pure endosperm, a mixture of particles to which
bran is attached, and bran particles.
 This is achieved by using sieves and air currents.
 The purifiers classify the material into several fractions
according to size, shape, and specific gravity.
 The endosperm particles, essentially free from bran and germ,
are spouted to smooth rolls, where they are ground into flour.

 Other particles to which bran and other outer layers of kernel

adhere are delivered to different pairs of rolls ("sizings") for
careful reduction and separation of the bran.

4.Sizings
 The material at each of the sizing stages is a mixture of

particles close in size range, some pure endosperm, and others
still with attached bran.
 The objective of the sizing stages is to reduce the particle size

and, during reduction, to separate the still attached bran from
the endosperm.

 Material from the sizing stages can be diverted to purifiers, to

middlings for final reduction, or to flour as a final product.
 However, the miller tries to refrain from severe grinding in

the sizing stage to avoid production of flour that may be
contaminated by the presence of bran.
 Some millers use corrugated rolls on sizing stages, while

others use smooth rolls.
 Smooth rolls will have a more delicate effect and produce

lower-ash flour than corrugated ones.


 When corrugated rolls are used in sizings stages, the

corrugation features are adjusted to the particle size and the
bran adhering to them.

5 Middlings or Reductions
 Coarse and fine pure endosperm particles from breaks,

purifiers, sizings, and reductions in the mill are reduced to
flour on smooth rolls.
 The outer layer of smooth rolls is of ''softer" steel than that of

corrugated rolls.
 The "softer" steel, which includes more carbon molecules in

the cast, "loses" them with time, thus keeping a rough surface.

 In general, the reduction system substantially affects the
quality of the end product through the compression and shear
applied on the endosperm matrix of protein in which starch
granules are embedded.

 In hard wheat the adhesion between the starch granules and
the protein matrix of the endosperm cells is stronger than in
soft wheat.

 Therefore, flours from soft wheat disintegrate easier in milling
and produce finer flours than those of hard wheats.

 Millers adjust the flowsheet and mill equipment to produce
flours of coarser granulation from weaker wheats and finer
granulation from stronger wheats to achieve optimum results
in baking. Prepared by Hab2 S. 46

 Starch damaged by milling absorbs five times more water during the

dough process and is susceptible to diastatic activity by enzymes that
decompose starch to dextrin, oligosaccharides, and simple sugars
during the dough preparation.

 When present at an excessive level, damaged starch has an adverse

effect on dough and bread quality.

 Because of its harder cell structure, hard wheat endosperm generates

flour with more damaged starch by the action of high roll pressure or
high impact forces during the reduction stages of the mill.

6. Air As a Means of Processing
 Machine location and product transfer in the mill are
optimized by maximizing the use of gravity flow for
intermediate materials.
 For vertical transfer of materials positive or negative
pneumatic systems are used.
 Negative pneumatic systems are usually used for the transfer
of all intermediate materials in the grinding unit.
 Properly designed and efficient air-handling systems for
pneumatic conveying or suction in various locations in the
mill reduce significantly the energy consumption of the
operation.
 In a modern mill about 10 times more air weight than wheat
weight is moved through the system.
 Accordingly, it is essential to maintain the relative humidity
at about 65% and temperature at about 25°C (77°F) in the mill
to control moisture evaporation inHab2 S. intermediate and final
Prepared by 48
products.

 In locations where extreme humidity levels or temperatures
exist, air control units should be installed in the mill.
 If intermediate stocks are too dry or too wet this affects the
sieving efficiency, the breaking up of the bran, and accordingly
the final quality of the flours.
Mill Control
 Control of mill performance is a continuous chore of the miller
who sets methods and procedures to achieve optimal
performance.
 As an example, when changing wheat mixes in the mill, the
flours are directed to a set-off bin until the mill is adjusted for
the new wheat mix.
 The mill flours are directed to the set-off bins also upon
starting and shutting down the mill.

 The reason for such measures is to prevent production of off-

grade flours while the mill is underloaded.
 The flour in the set-off bins is reblended to the main stream

at a very low rate.
 Scales to weigh wheat at receiving point, before and after

cleaning, tempered wheat, and final products could indicate
changes in loads, extraction levels, and any other problems in
each section of the mill.


 On-line instrumentation to determine moisture, protein, ash,

and color ensures uniformity of raw materials and final
products.
 Evaluation of the mill technological performance is measured

by using the ash content of wheat, intermediate materials,
individual flour streams, and final products.
 The significant difference in ash content among the three

main parts of the wheat kernel endosperm, bran, and germ is
used as a measure to determine the level of the separation
efficiency from each other.

 However, in the past, because no other accurate tools were
available, ash was used as a criterion of flour quality.

 Flour ash was an inconclusive parameter and in the past
created significant economic losses to millers and bakers.
 The reason is that ash values of flours are not directly related
to the flour end user's specifications.

 Millers compromised on flour extraction to supply flour
within specifications from good baking quality wheats that
inheritably had higher endosperm ash.

 Today, fast and accurate instrumentation to determine flour
qualities such as color, starch damage, rheological
characteristics, and baking qualities is widening the
parameters for flour specifications.

 The objective in milling is to achieve as high as possible flour
extraction with the lowest contamination of bran and germ
that increase ash content.
 The ash curve is a mean to express cumulative ash of the flour
streams in the mill.

 To construct the ash curve the streams are arranged in
increasing order of ash content, and they are weighted based
on the extraction of each into a function that is a relationship
between the cumulative ash content of a number of streams
and the related total flour extraction fig .

 The miller's objective is to reach an ash curve that is flat and
start to turn upward at the highest possible flour extraction.


 While the ash values and curve are an indication of the mill
separation efficiency between the endosperm and bran, the
granulation curve is a function of mill adjustment and screen
selection.
 The granulation curve (Fig. 4) expresses the disintegration of
the wheat kernel at different stages of the milling process.
 The curve is drawn as a graph where the horizontal axis shows
the various sieve apertures in micrometers, and the vertical
axis shows the cumulative percentage tailovers of the
respective sieves.
 The granulation curve shows the particle size distribution of
the ground material.
 By drawing granulation curves for each of the grinding stages,
the miller can monitor variability in kernel disintegration and
make the necessary adjustments in the system.
 The data to construct the granulation curve can be generated
with an experimental sifter.

 The miller sieves the stock from under the rollstand on a

stack of sieves and then calculates the percentages of all the
quantities remaining on the sieves and the material in the
bottom pan from the total weight.


 If a different set of sieves is used for the separation of a

grounded stock, different points will be allocated on the
same graph to determine a change in the amount overtailing
from each sieve.
 The shape of the curve does not depend on the sieve

aperture, but on the sample granulation distribution.
 The miller draws the granulation curves of the mill for each

wheat mix at the time when mill performance is optimum.
 Granulation curve analysis can generate the following

information: (1) corrugation condition, (2) mill balance, (3)
roll adjustment, and (4) sieve area, aperture, division, and
efficiency of the sieving stages. by Hab2 S.
Prepared 58

A. Flours
 Flour quality is a subjective concept that relates to final
product usage.
 For different types of bread around the world specific wheat
characteristics and flour qualities are required.
 Quality parameters such as color, protein, granulation
distribution, gluten quantity and quality, and starch damage
play a role in the suitability of flour for the baker.
 Another important factor besides the determination of
quality is the concept of flour uniformity.

 For the commercial baker uniformity of flour supplied is
more important than variations in characteristics such as
premium protein or reduced starch damage.

 Flours from the different stages in the mill are not identical in
physical appearance, chemical analysis, or baking properties.
 These flour streams are composed of varying amounts of
different parts of the wheat kernel.
 In the case that all the flour streams are blended to one
composite, the result is a ''straight-grade flour."
 The quality of the straight-grade flour is directly related to the
quality of the processed wheat.
 It is possible to combine these flour streams in different ratios
to produce simultaneously two or more final flours that differ
in color, ash content, protein content, dough-handling
properties, and bread baking characteristics.
 This method of producing more than one final flour from one
wheat mix is called "split milling" or "divide milling."

 In wheat-importing countries the method of split milling is
used to accommodate the requirements for flour qualities of
different end uses.
 In wheat-growing countries such as the United States split
milling is not frequently used since the wide variety of wheat
types accommodate different end uses.
 In the United States the common types of flours produced in
a mill are patent, first clear, and second clear.

 Amounts and types of final products vary among mills are a
result of differences in flow-sheet, adjustments, and kinds of
wheat milled.
 Flour streams from the head end middlings, primary sizings,
and in some cases that of second and third breaks originate
from the center of the wheat kernel.

 The blend of these flour streams is called ''patent flour."
 Patent flour is about 77% of the total flour, is the whitest, and
contains the lowest relative amount of ash (0.38-0.42%,
corrected to 14% moisture basis( m.b.).
 Other flour streams of the process that contain a higher
percentage of the endosperm parts adjacent to the bran and
germ are distinguished from the former by higher ash and
protein contents, darker color, and inferior baking qualities.
 These flour streams can be combined to make up "first-clear
flour."
 First-clear flour is about 20% of the total flour and contains
about 0.75% ash.
 "Second-clear flour," made up of the rest of the streams, is 3%
of total flour and contains up to 1.2% ash (14% m.b.).


 The ratio between patent, first clear, and second clear could

vary substantially in percentages in other instances and,
accordingly, in ash and quality.
 Blending part or all of the first clear into the patent comprises

the "baker's patent.“
 Control of flour particle size distribution is a parameter the

miller controls by wheat selection, tempering, mill flow, and
mill adjustment.


 The miller subjectively blends the flour streams from

different stages in the mill to make up the final products.
 Optimum flour granulation distribution is an important

parameter for the baking process.
 Drastic change in granulation effects water absorption, water

retention during fermentation, proofing, and quality of
finished breads.
 The mill adjusts product granulation to the kind of additives

added during dough preparation and to the types of breads
baked.


 The ash content does not affect the baking quality of the flour;

it relates basically to the level of bran in the flour.
 Ash content of flour is a very valuable test for mill control.

 However, in many cases flour ash is used in flour quality

specifications disproportionately to its value and significance
in baking.
 This creates a situation where millers are constrained to lower

flour extraction when using good baking quality wheat of
inherently high endosperm ash.


 Flour color depends on wheat cleanliness, tempering level,

finesse of flour, and the amount of bran particles it
contains.
 Too much fine bran effects flour shade, producing a darker

shade.
 Frequently during the mill operation the miller slicks a

flour sample and wets it. This method, called the Pekar
test, is used by the miller to evaluate the color and amount
of bran particles in the flour.
 Change in mill ambient conditions could also affect flour

color.

 In addition, flour carries a yellow cast due to the presence of

carotene.
 Natural aging during storage of the flour for up to 2 weeks or

usage of different bleaching agents, where permitted, could
overcome this problem.
 In mills where microingredients are added to flour according

to customers' specifications, they are introduced into large-
capacity, high-speed batch mixers during final blending and
before load-out.


 In some countries improvers and enrichments are fed into

the flour in the mill or in the blending facilities before load-
out.
 The powders are added to the flour with great accuracy and

uniformity by special feeders.
 Modern systems use programmable logic controller (PLC)-

controlled feeding systems.
 At the end of the milling process the microingredients are

conveyed by air and introduced and mixed into the flour by
special agitators.

B Bran
 Commercial bran differs from the botanical outer layers of
the wheat kernel.
 The bran that is removed during the various stages of the

milling process is made up of fractions that differ in size and
endosperm content.
 Bran is described using factors such as minimum protein,

minimum fat, maximum fiber, and maximum moisture.
 In the United States "wheat mill bran" would be a product

that includes all offal fractions from a typical mill.


 According to the American Feed Control Officials [66],
wheat mill run consists of the following: minimum
protein, 13.0%; minimum fat, 4.0%; maximum fiber, 9.5%;
and maximum moisture, 14.0%.
 The loosely held embryo part of the germ can be extracted
relatively easily, but the soft scutellum, high in fat and
protein, is difficult to separate from the endosperm and
the bran .


 The American Feed Control Officials define proximate analysis for

all other by-products from the milling process.
 Specifications will vary from country to country based on milling

technology, feed regulations, kind of wheat used, and climatic
conditions.
C . Wheat Germ
 The germ constitutes about 2.53% by weight of the wheat kernel

depending on the size of the whole kernel.
 The two main parts of the wheat germ are the embryo and the

scutellum.



 The embryo and the whole germ differ in size, shape, and the

level at which they are embedded into the kernel among the
different kinds of wheat.
 The mill flow is designed to separate whole embryos during

the breaking stages.
 The moist, soft, and easily flattened embryos are directed in

the mill flow, usually from a purifier, to a pair of smooth rolls
with low differential, where they are flaked.
 The small flakes are extracted in the sifters over a 14 US mesh

sieve (1410 mm).

 According to definitions of the Association American Feed Control

Officials, pure wheat germ that is used primarily for human food
should contain a minimum of 30% protein.
 In some mills the germ is separated with an impact machine ahead

of the first break roll.
 After impaction the material is sifted on a sifter, where it is

separated into different fractions.
 The coarse material is diverted to the first-break coarse, the

intermediate material to first-break fine, and the fines containing
the embryos to a smooth pair of rolls, where it is flaked for
separation.


A .Protein
 Various classes of wheat are intentionally bred and selected for
a specific composition, usually to meet end-use requirements
for a product.
 For example, commercial soft wheats are maintained at low
protein levels, although certain soft wheats are associated with
genes for high protein and are used as germplasm in breeding
programs to develop high-protein hard wheats.
 Protein content in a single variety of wheat can vary from 7 to
20% depending upon growing environment and fertilizer use.
 The high-protein hard wheat is higher in protein in all
constituents except the germ.


 Constituents of wheat grains are not distributed uniformly.

 The pericarp (bran) is high in pentosans, cellulose, and ash.

 The aleurone is a botanical part of the endosperm, but during

milling it is removed with the bran.
 With an increase in extraction rates, protein, fat, and fiber

increase, whereas carbohydrates decrease.
 It is commonly accepted that the protein content of straight-

grade flour is about 1% less than that of the wheat used by the
mill.


 It is high in protein, lipids, pentosans, and ash, thus
contributing significantly to the nutritional quality of bran as a
feedstuff. Starch is found in the endosperm.
 The outer endosperm (subaleurone) is higher in protein than

the inner portion.
 The embryo and scutellum, which make up the germ, are high

in protein, lipids, reducing sugars, and ash.
 Because of the structure of various parts, milling extraction

rates affect flour composition.


 The miller controls variation in flour protein by adjusting wheat

protein, wheat size, and wheat-blending methods.
 The protein ''difference" between the whole kernels and flour is

larger for smaller size kernels .
 In cereals only wheatand to some extent ryehave storage proteins

that form the gluten network in flour and water doughs, which has
the unique properties of elasticity and strength to produce yeast-
leavened bread.
 Storage proteins comprise 85% of wheat endosperm proteins and

consist of gliadin (alcohol-soluble) and glutenin (alkali- or acid-
soluble) fractions.


 The amino acid composition, Glutamic acid and proline are
highest in the endosperm.
 Lysine, argenine, aspartic acid, and alanine are lowest in the
wheat and flour.
 Lysine is the limiting essential amino acid in wheat and most
cereals.
B .Lipid
 Lipid contents of wheat grains typically range from 2 to 4%.

 Lipid material is not dispersed evenly throughout the grain.
 The embryo (germ) contains 30% of its weight as oil.
 Commercial germ is in the 10-11% range.

 The endosperm is lowest in oil, and the outer layers have an
intermediate lipid level Prepared by Hab2 S. the
between germ and the
78
endosperm.

 Wheat germ oil includes a high proportion of unsaturated fatty

acids.
C .Vitamins and Minerals
 Vitamins are found in high concentrations in wheat germ and bran,

and minerals are especially concentrated in the bran.
 Whole kernel data for each are influenced by kernel size and the

ratio of bran to endosperm, which may be higher in small kernels.
 Kernel size can be influenced by environmental stress or genetic

factors.
 Milling and the degree of flour extraction will also affect vitamin

and mineral analysis on flour and other milled products.


A. Durum Wheat Milling
 Usually drum wheat is milled into a granular product called

semolina for pasta production.
 Depending on the pasta manufacturing system, ranges of

semolina granulation and particle distribution will vary.
 Regulations by the U.S. Federal Drug Administration define

semolina as a product made only from durum wheat that
passes through a No. 20 sieve, not more than 3% passing
through a No. 100 sieve.
 Its moisture content is not more than 15% and maximum dry

ash content is 0.92%. Prepared by Hab2 S. 80

 Durum wheat is also milled to flour of a granulation finer

than 200 mm in some parts of the world for local bread
baking.
 The extraction of final products based on wheat entering the

durum semolina mill ranges from about 65.70, 10, and 25.20%
of semolina, flour, and bran, respectively.
 Couscous is made from very coarse durum semolina with a

particle size range between 550 and 1100 mm.
 Couscous is not extruded, but is coagulated and steamed in

granular form.

 The granulation distribution of the semolina affects water

absorption of the particles during hydration in a pasta-
production process.
 Subsequently, it also affects the drying of the pasta and its

quality.
 Optimum semolina granulation for each pasta product is a

major concern of the miller and pasta manufacturer.
 Common semolina particle size for long pasta is finer than 630

mm and for short goods finer than 350 mm.


 Durum wheat semolina is evaluated based on speck count,

protein level, and ash.
 The origin of specks in the semolina could arise from different

sources.
 Generally about 45% originate from discolored germs, 25%

discolored endosperm, 15% bran particles, 10% grit, and 5%
other sources.
 Ergot, when present in wheat, could show up as specks in the

semolina.


 Durum and spring wheat, like other cereals that might go

through the flowering period during cold and wet
weather, could be infected by the fungus Claviceps
purpurea or ergot.
 Ergot is a fungus that produces alkaloids toxic to humans

and animals when it invades spring wheat, durum wheat,
and rye.


 The word ''ergot" is applied to both the fungus and the disease that

the fungus causes.
 Hard wheats are more vulnerable to ergot attack than soft wheats.

 Hybrid varieties are more susceptible presumably because they have

smaller anthers with less than sufficient pollen for quick
fertilization, resulting in sensitivity to ergot attack.
 Millers use different methods such as gravity tables and color sorters

to separate ergot from the wheat.
 According to U.S. Department of Agriculture Standards for Grain,

ergoty wheat is wheat that contains more than 0.05% percent ergot.


 The specks have an adverse effect on the aesthetic appearance

of pasta and, to some extent, the resistance to breakage of
long varieties.
 Grit content in the granular semolina is also a quality

measure.
 Grit originates from ground stones not separated from the

wheat during cleaning.
 Grit in semolina could damage the pasta extruder's surface.


 Durum milling is substantially different from flour milling.

 To achieve maximum extraction of granular endosperm,

more break and corrugated sizing stages are used.
 The tail-end materials in the mill that could not be

extracted as semolina are usually ground on smooth rolls
to flour.


 Although the total cumulative break release would be the same,

the release on the individual breaks is lower than in flour milling.
 The number of purifiers used in semolina milling is significantly

higher than in conventional flour milling.
 The purifier is the machine from which the final semolina is

extracted.
 In durum milling the miller sends material to purifiers with much

narrower particle size ranges than in flour milling to differentiate
more sharply between the different characteristics of materials
based on size, shape, and specific gravity.


B .Soft Wheat Milling
 The soft wheat milling process differs from that for hard

wheat because of the softer kernel endosperm.
 Soft wheat is milled to flour that is used mainly for the

manufacture of baked goods not requiring a developed
structure during fermentation.
 Protein contents of flours produced in the soft wheat mill

ranged from 4.7 to 9.1% and patent ash contents from 0.23 to
0.42% (14% m.b.).
 Soft wheat kernels are wider and have a lower specific weight

than hard wheat kernels.

 Accordingly, cleaning machinery must be adjusted to the physical

characteristics for efficient separation of unmillable materials.
 The endosperm structure of soft wheat is not vitreous and dense,

allowing water to penetrate at a faster rate than in hard wheats
through the capillary spaces in the endosperm.
 Therefore, tempering time to reach a milling moisture is very short

for soft wheat, usually about one half of the time required by hard
wheat.
 In cases when the natural moisture of the wheat is high, only a

limited amount of water is sprayed on the wheat about 30 minutes
before milling to toughen the bran.

 Endosperm of soft and hard wheats fracture differently during

the milling process.
 Hard wheats are more crystalline and break into large chunks

of endosperm while soft wheat endosperm is amorphous and
crumbles into smaller particles.
 The soft endosperm disintegrates during the milling process

with less pressure.
 As a result, soft wheat produces finer flour particles with

lower levels of starch damage compared to hard wheat.


 In countries where soft wheat flours are used for bread baking,

the miller is aware that he or she has to control the starch
damage of the flour.
 This is done by applying heavy roll pressures in the reduction

system.
 Also, the starch protein bond in soft wheat is weaker than that

in hard wheat.
 With proper impact force, it is possible to separate the

granules from the protein matrix in which they are embedded.
 During milling more flour from breaks and less sizing
production are the main characteristics of soft wheats
compared to hard wheats. Prepared by Hab2 S. 92

 The sifter effective area in a soft wheat mill is relatively larger than

in the hard wheat mill.
 This should overcome difficulties in sieving of fine flours.

 Some millers overcome the difficulties of sifting soft wheat

materials by using centrifugal sifters.
 The centrifugal sifters might have advantages over regular gyrating

sifter boxes.
 The action of a centrifugal machine, in which a counter rotating

rotor throws the stock against a cylindrical sieve, allows efficient
separation, especially in the poorly flowing stocks of the soft milling
flow.


 In general, purifiers are not used in soft wheat mills.

 In cases where they are incorporated in the flow they treat

only the small amount of sizings from the primary breaks.
 The less rigid endosperm attached to the bran in the tail end

breaks is difficult to separate with conventional grinding rolls
that might splinter the bran.
 Impact dusters are used before the third, fourth, and fifth

break rolls to achieve more flour extraction.
 In general, more impactors are used in a soft wheat mill

between the rolls and sifters to increase flour extraction
compared to hard wheat milling.

 There is a new technical approach to the separation of the

three main parts of the wheat kernel: endosperm, bran, and
germ.
 The new technology applies intensive and accurate abrasion of

the wheat kernel bran. The miller can selectively remove
wheat pericarp layers from the outside in.
 The objective of the new technology is to break up the

structure of the kernel in such a way that the crease
''structure" will stay intact.
 This technology reduces to a large extent the number of

machines in the mill. Prepared by Hab2 S. 95

 The benefits of such a technology are reduced capital

investment, shorter milling process, reduction in energy,
reduction of a-amylase content of flour when partially
sprouted wheats are used, and reduction of fragments and
bacteria count in flours.
 The rapid developments in electronics and instrumentation

are implemented in the mill for rapidly sensing online the
quantitative and qualitative characteristics of mill products.


 Evaluation of intermediate and final mill products allows the

development of mill automation and control.
 Near-infrared reflectance, fluorescence imaging, microwave,

and electronic weighing are some of the current and future
areas of development.


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