Wheat cleaning

1. The purpose of wheat cleaning, due to the current technical constraints, wheat growth, harvest, storage, transportation and other processes will have impurities mixed. In the growing season, the wheat which is germinated and moldy because of too much rain and the wheat which is attacked by insects and diseases is the impurity in wheat, and the mixing of these wheat will affect the quality and odor of wheat flour.Therefore, in the milling wheat must be cleaned before, all kinds of impurities in wheat completely clean, so as to ensure the quality of flour, to meet the needs of the food industry and people's lives, to ensure people's health, and achieve the purpose of safe production.   

2. Classification of impurities impurities in the wheat can be classified according to the chemical composition and physical properties.

(1) According to the chemical composition

The inorganic impurities inorganic impurities mixed with clay and sand, refers to the brick, metal and other inorganic substances in wheat.   

The organic impurities organic impurities is mixed with wheat roots, stems, leaves, grass seed, shell, grain and edible dissimilar value buds, spots, metamorphic and other organic substances of wheat.It can be divided into three categories according to physical property and particle size of impurity.
①large impurities  Refers to the impurity retained in Diameter of 4.5 mm
 sieve screen surface.
②Side by side impurities Refers to the impurities through the diameter of 4.5 mm sieve screen surface, retained in the diameter of 1.5 to 2.0 mm sieve screen surface impurities.　　

③Small impurities  Refer to pass through the diameter of 1.5 ~ 2.0 mm sieve screen surface impurities. 

According to the specific gravity impurityies can be divided into two categories:　 

①Heavy impurities  Refers to the wheat  specific gravity is bigger than the impurities specific gravity.　 

②Light impurities Refers to wheat specific gravity is smaller than the impurities specific gravity.
 

3.Common methods of wheat cleaning　

(1)wind selection method  

The method of cleaning the air dynamics properties of wheat and impurities is called wind selection method.The aerodynamic properties are generally expressed as suspended velocities.wind selection method needs participation of air media.Commonly used air - selection equipment including vertical air duct and suction separator.

(2)Screening method 

The method of cleaning with different size of wheat and impurity is called screening method.Grain size is generally based on the thickness and width of wheat and impurities.The screening method needs to be equipped with a suitable screen for the movement of the sieve, and the relative motion of the sieve and the wheat is used to stratify the wheat.Small size and heavy flour would be pass through the sieve.

The commonly used screening equipment has vibrating screen, rotary flat sieve and pre-cleaning screen.

(3)Using different grivatity of wheat and impurity to separate them.It is called gravity separation method. The gravity separation method needs the participation of the medium, and the medium can be air and water. The use of air as a medium is called dry gravity separation; the use of water as a medium is called wet gravity separation. The proportion of dry separation equipment commonly used gravity destoner, gravity separation, gravity separation equipment commonly used in wet stone wheat washing machine etc.  

(4) selection method using impurities and wheat geometry and different length of cleaning method called selection method. It is necessary to use the inclined plane and the spiral surface to separate the wheat and the spherical impurity by the different geometric shapes. The common buckwheat seed throwing vehicles and other equipment. The use of different lengths for cleaning requires a rotating surface with a pocket. The short grain embedded bag holes are taken away, and the long grains remain outside the bag holes and are not taken away, so as to achieve the purpose of separation. Commonly used equipment has drum selection machine, disc selection machine, disc roller selection machine, etc.

(5) impact method by the impurity and wheat of different intensity cleaning method called impact method. Germination, moldy, diseases and insect pests of wheat, wheat and soil surface adhesion of dust, the adhesion strength is lower than that of wheat, the impact of the high-speed rotating component, broken off, the use of suitable mesh separating it, so as to achieve the purpose of cleaning. The impact of equipment commonly used are beating machine, impact machine, wheat brush machine etc.

(6) magnetic separation method using wheat and impurity ferromagnetic different cleaning method called magnetic separation method. Wheat is a non-magnetic material, in the magnetic field is not magnetized, thus cannot be absorbed by the magnets; and some metal impurities (such as iron nails, nuts, etc.) is a magnetic material in a magnetic field will be magnetized by the magnet adsorption, which is separated from wheat. Permanent magnetic drum, magnetic steel and permanent magnetic box are commonly used in magnetic separation.  

(7)Grinding method;

To clean up wheat surface dust or grind wheat straw by the use of rotating rough surfaces (such as sand grain) is known as the grinding method. It is widely used for peeling and milling. Through the grinding of the surface of a few sand rolls can partially separate the wheat flour, which can shorten the powder path and make it easier to pulverize. The commonly used equipment is like peeling machine etc.

In addition to the above methods, there are other methods,such as the one according to the color of the photoelectric sorting method, the equipment is color selection machine. The current application is not yet widespread as the equipment is very expensive.

(B) wheat moisture regulation

The moisture regulation of wheat, is to add the water and give it a certain time for moisture, so that to re-adjust the moisture of wheat and improve its physical, biochemical and milling process performance, in order to obtain better milling process effect. 

1. Physical and biochemical changes after adding water, the corresponding physical and biochemical changes occur:

(1) the moisture content of wheat is more, the grain has a similar moisture content and similar water distribution by a certain rule.

The first layer of water swelling, aleurone layer and endosperm followed by water swelling. Due to the three are with different orders in water swelling,so, there is a slight displacement in the radial direction of the wheat grain , then the combination between the three Force is weakened. This is favorable in separation of the cortex and the endosperm,and the powder can scrap from the cortex down easily.

Cortical after absorb the water, toughness increased ,

brittleness reduced, increasing its ability to resist mechanical damage. Therefore, in the grinding process this facilitate the preservation of bran slices and clean the bran film on the endosperm, to ensure the quality of flour and improve the extraction rate of flour. In addition, the integrity of the bran is also conducive to the sifting and bran brushing.

(4) the intensity of the endosperm is reduced. The starch and protein contained in the endosperm are crossed together. Protein water absorption capacity (large water absorption), slow water absorption; starch granules weak water absorption (small water absorption), fast water absorption. Because of the difference between the speed and ability of the two, the expansion of the different and the degree of difference, resulting in starch and protein particles displacement, so that the endosperm structure loose, reduced strength, easy to ground into powder, is conducive to reducing power consumption. In the case of.

(5) The yield of wet gluten increases with the increase of wheat moisture, but the quality of wet gluten is weakened. In the case of

(6) proteolytic enzyme activity, free amino acid content, saccharification activity, sucrose and a variety of reducing sugar content has changed. But little effect on the milling process. In the case of.

From the above changes can be seen, wheat moisture regulation, the milling process performance improved, can increase the rate of flour, improve the quality of finished flour, and reduce power consumption. In the case of

2. The corresponding process effect of wheat by water regulation, should be the corresponding process effects are as follows:

(1) so that the grinding of wheat with the appropriate water to meet the requirements of the milling process to ensure the relatively stable process of milling, easy operation and management. This is very important to improve production efficiency, flour yield and product quality. Requiring moisture uniformity within 0.2%. In the case of

(2) to ensure that flour moisture in line with national standards. Wheat dryness will cause the flour moisture is too low, so that the powder plant suffered losses; the other hand, wheat overheating will cause flour moisture is too high, not only will affect the interests of consumers, will also affect the flour storage management.   

The quality of wheat

Wheat varieties and quality is not immutable and frozen, therefore, the designing of the cleaning section flow should take into account factors like the number of impurities in wheat,proportion of hard wheat and soft wheat, and the content of water, etc.It’s better to adopt good cleaning equipment and water conditioning equipment. In actual production, for wheat with little impurity and high moisture, can adjust the shunting device, not have to pass through every equipment.
Considering the wheat producing areas of China, wheat