Wheat Milling
Faizan Ahmad
Assistant Professor
Post Harvest Engineering & Technology
Faculty of Agricultural Sciences
Aligarh Muslim University
Wheat Milling
• Wheat is a main food grain of many countries. it is one of the most
important cereal and used as staple food in the form of flour.
• In India a large proportion of wheat is used as atta (whole wheat flour)
and maida (white flour).
• The heard wheat are also ground into suji (semolina). Whole wheat is
ground into atta by traditional stone grinder (chakki) without prior
separation bran and germ.
Modern (Roller) Flour Milling:
• The objective of milling is to obtain maximum amount of white flour
from wheat endosperm without any bran or germ.
• Milling separates germ, because it contains lipids that could cause the
flour to go rancid and bran, because it is unappealingly dark and not
desired in the preparation of flour of many bakery products.
• The yield of white flour and by-products called mill feed from white
flour milling are about 70% and 30%, respectively.
• The mill feed comprises 12% bran, 3% germ and 15% shorts
(endosperm). Wheat consists of 12% bran, 3% germ and 85%
endosperm.
Steps involved in Modern Flour Milling:
Steps involved in Modern Flour Milling:
(a) Cleaning the wheat:
Aspirator- The aspirator sucks up foreign matter which is lighter than the
wheat and removes it.
Disc separator- it moves the wheat over a series of disks with
indentations that collect objects the size of a grain of wheat. Smaller or
larger objects pass over the disks and are removed.
Scourer- it scrape off dirt and hair by vigorous rubbing action of beaters.
Magnetic separator- with the help of magnets it removes small pieces of
metals.
Washer stoner-high speed rotors spin the wheat in the water bath. excess
water is thrown out by centrifugal force. stones drop to the bottom and
are removed. Lighter material float off leaving only the clean wheat.
(b) Preparing the wheat for grinding:
Tempering/Conditioning/Hydrothermal treatment:
• Aid the separation of bran from the endosperm and to provide
controlled amount of moisture and temperature throughout the milling.
• Moisture is added either at room temperature of at elevated temperature
not above 47oC. to retain gluten quality which affects baking quality of
wheat flour.
• Moisture of wheat rises 1-2%. Moisture content increase to 16-19% in
hard wheat varieties and 15-17% in soft varieties. Tempering is done for
18-72 h in tempering bins .
•
In modern system the conditioning is done in three stages.
 Preheating section
 Moistening section and
 Cooling section
• Conditioning can also be accomplished by direct steaming. Moistening
and heating is carried out simultaneously in a single operation.
• The grain is heated in just 20-30 s to 47oC. The rapid heating weakens
the bond between various parts of grain and facilitates their separation.
It also has stronger action of proteins and enzymes.
• Conditioning results in toughening of high cellulose containing parts
viz., germ and bran and softens the endosperm which facilitates size
reduction.
(c) Grinding the wheat:
• Breaker rolls-These rolls are of two different sizes and move at different
speeds.
• They also contain spiral grooves which crack open the grains of wheat and
begin to separate the interior of the wheat from the outer layer of bran.
• Generally a series of four sets of breaker rolls are used. Each roll set takes
stock from preceding breaker rolls.
• In addition to that a standby system of break rolls called scratch rolls is
also kept.
Breaker rolls
• After each break, mixture of free bran, free germ, free endosperm
and endosperm still adhering to bran is sifted and separated.
Sifter and Purifier-The product of the breaker rolls passes through metal
sieves and air current to separate it into three categories.
• The finest material resembles coarse flour and is known as middling's or
farina.
• The middling's move to the middling's purifier and the other materials
move to another pair of breaker rolls.
• About four or five pairs of breaker rolls are needed to produce the
necessary amount of middling's
• Larger pieces of the interior are known as semolina.
• The third category consists of pieces of the interior which are still attached
to the bran.
Reduction rolls
Reduction rollers- Middling's are ground into flour by pairs of large,
smooth metal rollers.
• Each time the flour is ground it passes through sieves to separate it into
flours of different fineness.
• These sieves are made of metal wire when the flour is coarse, but are
made of nylon or silk when the flour is fine.
• By sifting, separating, and regrinding the flour, several different grades
of flour are produced at the same time.