manufacturing of flour

8/10/2019 MAnufacturing of flour

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Flour

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Flour is a finely ground powder prepared from grain or other starchy plant food.

Raw Materials

Although most flour is made from wheat, it can also be made from other starchy plant foods.

These include barley, buckwheat, corn, lima beans, oats, peanuts, potatoes, soybeans, rice, and

rye. Many varieties of wheat exist for use in making flour. In general, wheat is either hard

(containing 11-18% protein) or soft (containing 8-11% protein). Flour intended to be used to

bake bread is made from hard wheat. The high percentage of protein in hard wheat means the

dough will have more gluten, allowing it to rise more than soft wheat flour. Flour intended to be

used to bake cakes and pastry is made from soft wheat. All-purpose flour is made from a blend

of soft and hard wheat. Durum wheat is a special variety of hard wheat, which is used to make a

kind of flour called semolina. Semolina is most often used to make pasta.

Flour usually contains a small amount of additives. Bleaching agents such as benzoyl peroxide

are added to make the flour more white. Oxidizing agents (also known as improvers) such as

potassium bromate, chlorine dioxide, and azodicarbonamide are added to enhance the baking

quality of the flour. These agents are added in a few parts per million. Self-rising flour contains


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salt and a leavening agent such as calcium phosphate. It is used to make baked goods without the

need to add yeast or baking powder. Most states require flour to contain added vitamins and

minerals to replace those lost during milling. The most important of these are iron and the B

vitamins, especially thiamin, riboflavin, and niacin.

The Manufacturing Process

Grading the wheat

1.

Wheat is received at the flour mill and inspected. Samples of wheat are taken for

physical and chemical analysis. The wheat is graded based on several factors, the most

important of which is the protein content. The wheat is stored in silos with wheat of the

same grade until needed for milling.

Purifying the wheat

2. Before wheat can be ground into flour it must be free of foreign matter. This requires

several different cleaning processes. At each step of purification the wheat is inspected

and purified again if necessary.


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3. The first device used to purify wheat is known as a separator. This machine passes the

wheat over a series of metal screens. The wheat and other small particles pass through the

screen while large objects such as sticks and rocks are removed.

4. The wheat next passes through an aspirator. This device works like a vacuum cleaner.

The aspirator sucks up foreign matter which is lighter than the wheat and removes it.

5. Other foreign objects are removed in various ways. One device, known as a disk

separator, 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.

6. Another device, known as a spiral seed separator, makes use of the fact that wheat grains

are oval while most other plant seeds are round. The wheat moves down a rapidly

spinning cylinder. The oval wheat grains tend to move toward the center of the cylinder

while the round seeds tend to move to the sides of the cylinder, where they are removed.

7. Other methods used to purify wheat include magnets to remove small pieces of metal,

scourers to scrape off dirt and hair, and electronic color sorting machines to remove

material which is not the same color as wheat.

Preparing the wheat for grinding

8- 8 The purified wheat is washed in warm water and placed in a centrifuge to be spun dry.

During this process any remaining foreign matter is washed away.


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9- The moisture content of the wheat must now be controlled to allow the outer

layer of bran to be removed efficiently during grinding. This process is known as conditioning or

tempering. Several methods exist of controlling the amount of water present within each grain of

wheat. Usually this involves adding, rather than removing, moisture.

10- Cold conditioning involves soaking the wheat in cold water for one to three days. Warm

conditioning involves soaking the wheat in water at a temperature of 115F (46C) for

60-90 minutes and letting it rest for one day. Hot conditioning involves soaking the wheat

in water at a temperature of 140F (60C) for a short period of time. This method is

difficult to control and is rarely used. Instead of water, wheat may also be conditioned

with steam at various temperatures and pressures for various amounts of time. If

conditioning results in too much moisture, or if the wheat happens to be too moist after

purification, water can be removed by vacuum dryers.

Grinding the wheat

11- Wheat of different grades and moistures is blended together to obtain a batch of wheat

with the characteristics necessary to make the kind of flour being manufactured. At this

point, the wheat may be processed in an Entoleter, a trade name for a device with rapidly

spinning disks which hurl the grains of wheat against small metal pins. Those grains

which crack are considered to be unsuitable for grinding and are removed.


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12-The wheat moves between two large metal rollers known as breaker rolls. These rollers

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. The product of the breaker rolls passes through metal sieves to

separate it into three categories. The finest material resembles a coarse flour and is

known as middlings or farina. 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. The

middlings move to the middlings 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 middlings.

13- The middlings purifier moves the middlings over a vibrating screen. Air is blown up

through the screen to remove the lighter pieces of bran which are mixed with the

middlings. The middlings pass through the screen to be more finely ground.

14- Middlings 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. These are combined as needed to

produce the desired final products.


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Processing the flour

15- Small amounts of bleaching agents and oxidizing agents are usually added to the flour

after milling. Vitamins and minerals are added as required by law to produce enriched

flour. Leavening agents and salt are added to produce self-rising flour. The flour is

matured for one or two months.

16-The flour is packed into cloth bags which hold 2, 5, 10, 25, 50, or 100 lb (About 0.9, 2.3,

4.5, 11.3, 22.7, or 45.4 kg). For large-scale consumers, it may be packed in metal tote

bins which hold 3000 lb (1361 kg), truck bins which hold 45,000 lb (20,412 kg), or

railroad bins which hold 100,000 lb (45,360 kg).

Quality Control

The quality control of flour begins when the wheat is received at the flour mill. The wheat is

tested for its protein content and for its ash content. The ash content is the portion which remains

after burning and consists of various minerals.

During each step of the purification process, several samples are taken to ensure that no foreign

matter ends up in the flour. Since flour is intended for human consumption, all the equipment

used in milling is thoroughly cleaned and sterilized by hot steam and ultraviolet light. The

equipment is also treated with antibacterial agents and antifungal agents to kill any microscopic

organisms which might contaminate it. Hot water is used to remove any remaining traces of

these agents.


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The final product of milling is tested for baking in test kitchens to ensure that it is suitable for the

uses for which it is intended. The vitamin and mineral content is measured in order to comply

with government standards. The exact amount of additives present is measured to ensure

accurate labeling.

Byproducts/Waste

A kernel of wheat consists of three parts, two of which can be considered byproducts of the

milling process. The bran is the outer covering of the kernel and is high in fiber. The germ is the

innermost portion of the kernel and is high in fat. The endosperm makes up the bulk of the kernel

and is high in proteins and carbohydrates. Whole wheat flour uses all parts of the kernel, but

white flour uses only the endosperm.

Bran removed during milling is often added to breakfast cereals and baked goods as a source of

fiber. It is also widely used in animal feeds. Wheat germ removed during milling is often used as

a food supplement or as a source of edible vegetable oil. Like bran, it is also used in animal

feeds.


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manufacturing of flour

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