Vital Wheat Gluten

Flour is also taken as the raw material for the three-phase horizontal spiral centrifuge process. Flour approaching special Grade II shall be selected if possible, featuring high flour yield, high wheat gluten content, low ash content, and low starch damage rate.

After metering, raw flour is introduced into a mixer to mix with water forming slurry, with flour-to-water ratio approximately 1:(0.85-0.95). The mixer enables flour particles to fully hydrate, forming uniform slurry. Large particles with uneven mixing and uneven small dough lumps must not exist, to facilitate subsequent homogenization process.

After mixing comes homogenization. Slurry is pumped into a homogenizer. Homogenizer pressure can be adjusted by changing homogenization valve clearance, with pressure up to 100 bar (1 bar = 105ba). When slurry passes through the homogenization valve, high pressure rapidly restores to normal pressure. Due to abrupt pressure change and shearing action of the homogenization valve, slurry gelatinizes and achieves rapid aggregation of protein network. The homogenizers which are commonly used in dairy industry are selected for the homogenization.

Homogenized and gelatinized slurry is conveyed by eccentric screw pump to three-phase horizontal spiral centrifuge for component separation. Before entering the machine, certain amount of fresh water and process water may be added to dilute slurry. However, water added in this process is less than in Martin method, approximately 0.3-0.9t per ton of flour required. Solid is the largest part in feed material. After the separation by horizontal spiral centrifuge, it is pushed by screw conveyor and discharged as underflow. Overflow is discharged by a built-in centripetal pump, which can rapidly discharge foam-like material formed in the process without the need for conveying pump. Because pentosan density is relatively small, it mainly distributes in overflow. Thus, this viscous material is separated from wheat gluten at the front end of process, reducing fresh water volume required in the process. 

Wheat gluten and water are fed into continuous gentle mixer according to certain ratio for mixing and stirring.  After full kneading, proteins in flour uniformly contact water and undergo hydration, continuously outputting toothpaste-like flour paste. Then it is sent to final cooking tank for gelatinization. After stirring, partial starch is liberated; meanwhile, wheat gluten-like proteins aggregate into filamentous tiny wheat gluten. At this stage, pump conveys it to horizontal spiral sedimentation centrifuge with separation factor 3,000-4,000 for separation. Gelatinized paste is separated into two phases due to different sedimentation velocities of starch and wheat gluten. Starch is discharged as concentrated phase from separator with underflow due to greater density; wheat gluten due to smaller density is discharged as light phase from separator with overflow. After starch removal by cylindrical pre-cleaner washing, wet wheat gluten is obtained and then sent to gluten dryer for drying to obtain gluten.

Underflow separated by three-phase horizontal spiral centrifuge is typically diluted with process water, then sent to centrifugal screens to remove residual fibers, and subsequently multi-stage hydrocyclone for washing, generally 12-stage starch washing hydrocyclone is provided. Underflow still contains some small B-starch, pentosan and fine fibers. To better separate them, this process adopts a vertical high-speed three-phase disk nozzle centrifuge placed before hydrocyclone group, cooperating with hydrocyclone to ensure efficient and thorough starch washing.

Underflow and overflow obtained from three-phase horizontal spiral centrifuge are separately sieved to recover more block-forming wheat gluten. Recovered wheat gluten is returned to process and treated together with middle phase, and the resulting wet wheat gluten is further dehydrated and dried into gluten.

Pentosan in overflow can be directly used as feed in liquid state, or enzymatically reacted to separate solid part; liquid part is concentrated with process wastewater, then dried with fibers as feed.

Coarse starch milk obtained from the bottom of horizontal spiral centrifuge is a mixture containing small amount of fibers and protein. Fibers are screened out by three-stage centrifugal screens in series, and then sent to drying system to obtain bran after drying.

Graded and refined A-starch milk is sent to fully automatic scraper centrifuge for dehydration, then dried by pneumatic drying system to obtain relatively pure A-grade starch. B-grade starch milk obtained from classification system has lower concentration. Starch can be collected from highly dispersed suspension by the concentration of horizontal spiral centrifuge. Tiny wheat gluten separated from horizontal spiral centrifuge is filtered to remove starch, and collected, then mechanically dehydrated and sent to ring-type gluten drying system for drying to obtain gluten.