To (1) determine the effect of mill speed on fractionation of pinto beans, and (2) to determine the effect of bean type on milling and fractionation


Pulse seeds are considered to be healthy due their high concentration of protein, high fiber, high levels of vitamins and minerals, and low fat. In order to increase their utilization, pulses can be milled to flour and incorporated in food products such as bread, cookies, cakes, and dry soup mixes. Milling and fractionating pulses into various particle size can potentially produce a broad range of products with different nutrient content and functionality. The purpose of this lab will be to first investigate the effect of milling speed on bean flour fractionation and then to investigate how different beans fractionate after milling at a determined speed (10000 rpm). A ZM 200 Retsch centrifugal mill consisting of a 12 tooth rotor and 2.0 mm sieve will be used to mill the pulses. This will be followed by fractionation of particulates using a Ro-tap RX-29-E Test Sieve Shaker staked with Tyler 7 sieves (20, 30, 40, 50, 60, 70 and 80 mesh).


Part 1

  1. Weigh 7 batches (in duplicate) of dry pinto beans weighing 200 g
  2. Mill beans in Retsch mill at 6000, 8000, 10000, 12000, 14000, 160000 and 18000 rpm, by manually feeding seeds intohopper
  3. Collect flour and fractionate in Ro-tap for 20 minutes by selecting the “fine sieve” option
  4. Weigh fractionates and calculatepercentage(make sure to clean sieves thoroughly using compressed air)

Part 2

  1. Weigh 200 g of each pulse (great northern bean, lima bean, black bean, lentil, mayocoba, bean, red kidney bean, chick pea) in duplicate
  2. Mill and fractionate as previously described

Lab Questions

  1. Prepare a line graph showing mill speed versus percentage of pinto bean fractions
  2. Prepare a bar graph showing the percentage of individual fractions for each pulse
  3. What is the primary type of force applied in the centrifugal mill?
  4. Identify and list factors that influence flour yield i.e. particles less than 212 µm
  5. What changes could you make to the process to increase flour yield?

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Courtney Simons
Courtney Simons
Dr. Simons is a food science educator. He earned his bachelor’s degree in food science, and Ph.D. in cereal science at North Dakota State University.