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Semiautomated, Reproducible Batch Processing of Soy

Processing conditions are selectable and are consistent from batch to batch.

A computer-controlled apparatus processes batches of soybeans into one or more of a variety of food products, under conditions that can be chosen by the user and reproduced from batch to batch. Examples of products include soy milk, tofu, okara (an insoluble protein and fiber byproduct of soy milk), and whey. Most processing steps take place without intervention by the user. This apparatus was developed for use in research on processing of soy. It is also a prototype of other soy-processing apparatuses for research, industrial, and home use.

Prior soy-processing equipment includes household devices that automatically produce soy milk but do not automatically produce tofu. The designs of prior soy-processing equipment require users to manually transfer intermediate solid soy products and to press them manually and, hence, under conditions that are not consistent from batch to batch. Prior designs do not afford choices of processing conditions: Users cannot use previously developed soy processing equipment to investigate the effects of variations of techniques used to produce soy milk (e.g., cold grinding, hot grinding, and pre-cook blanching) and of such process parameters as cooking times and temperatures, grinding times, soaking times and temperatures, rinsing conditions, and sizes of particles generated by grinding. In contrast, the present apparatus is amenable to such investigations.

Image The apparatus (see figure) includes a processing tank and a jacketed holding or coagulation tank. The processing tank can be capped by either of two different heads and can contain either of two different insertable mesh baskets. The first head includes a grinding blade and heating elements. The second head includes an automated press piston. One mesh basket, designated the okara basket, has oblong holes with a size equivalent to about 40 mesh [40 openings per inch (≈ 16 openings per centimeter)]. The second mesh basket, designated the tofu basket, has holes of 70 mesh [70 openings per inch (≈ 28 openings per centimeter)] and is used in conjunction with the press-piston head. Supporting equipment includes a soy-milk heat exchanger for maintaining selected coagulation temperatures, a filter system for separating okara from other particulate matter and from soy milk, two pumps, and various thermocouples, flow meters, level indicators, pressure sensors, valves, tubes, and sample ports.

A typical process carried out in this apparatus comprises the following steps:

  1. Dry soybeans are placed into the okara basket of the processing tank.
  2. The grinding/heating head is put in place, and a drain valve in the tank closes automatically.
  3. Water is added to the tank automatically, and the beans are soaked for a programmed time.
  4. The drain valve opens automatically to dump the soaking water.
  5. The beans are rinsed and drained automatically a selected number of times, each time using a selected amount at a selected temperature.
  6. The valve closes, and a selected amount of water at a selected temperature is added automatically. The beans can then be cooked, blanched, and/or ground as chosen by the user. For the sake of example only, the subsequent steps are based on a process known in the soy industry as the Illinois cook process.
  7. The beans are blanched for a selected time.
  8. Blanching stops automatically and the valve opens, draining the blanching water.
  9. The beans are automatically rinsed with cold water, which is then drained.
  10. The valve closes. A selected amount of water chilled to a selected temperature is added to the beans automatically.
  11. The beans are automatically ground and cooked as user has specified.
  12. The user removes the grinder/heater head and replaces it with the press head.
  13. Warm water automatically begins to circulate in the holding or coagulation tank.
  14. Chilled water is fed to the heat exchanger.
  15. The valve opens, and soy milk is automatically pumped through the heat exchanger and selected filters. The soy milk reaches the holding tank at a specified temperature, coagulant is added, and the solution remains at that temperature until coagulation is complete.
  16. During coagulation, the press head and okara basket are removed from the processing tank, then the press head is reinserted with the tofu basket.
  17. Once coagulation is complete, the mixture is made to flow back into the processing tank.
  18. The piston is actuated to press the tofu according to the user’s specification.
  19. The piston is retracted, then the user removes the head, retrieves the basket, and adjusts the bottom of the basket to release the tofu.

This work was done by Mary Toerne, Ivan W. Byford, Jack W. Chastain, and Beverly E. Swango of Johnson Engineering Corp. for Johnson Space Center. For further information, contact the Johnson Commercial Technology Office at (281) 483-3809. MSC-23313