Milling of Cereals Questions and Answers

Answer: C

Correct answer: They are smooth and run at equal speed

This is the false statement, and it describes the reduction rolls instead. Break rolls are fluted and run at a differential of two and a half to four to one, because they need shear to split the kernel and scrape endosperm from the bran. Reduction rolls are smooth and run at about 1.25 to 1, grinding clean semolina by compression.

Answer: D

Correct answer: Raising the extraction rate

Raising extraction is the one change that increases ash rather than reducing it, since it draws in the fractions nearest the bran. The other three all help: better purification removes bran flakes from the semolina, proper conditioning keeps the bran in flakes rather than shattering it into the flour, and removing more bran before the reduction passages keeps it out of the flour stream altogether.

Answer: A

Correct answer: The germ is harder than the endosperm

Hardness is not the issue, and the germ is in fact softer and more plastic than the endosperm - which is part of why it flattens rather than grinding, and can be sifted out. The reasons for removing it are that its oil turns rancid and shortens shelf life, that it darkens the flour, and that the oil is worth recovering separately.

Answer: B

Correct answer: Doubtful: fissured kernels break anyway

Whitening pressure is one cause of breakage but not the main one. Kernels fissured during drying will break under whatever pressure is needed to remove the bran, so reducing it merely trades head rice yield against degree of milling. The recovery has to be made at the drying stage, by drying slowly and evenly and not rewetting.

Answer: C

Correct answer: It is mineral-rich and leaves with the bran

The aleurone is a single layer of cells lying just inside the seed coat and forming the outermost part of the endosperm botanically, though it is removed with the bran in milling. It is rich in protein, minerals and vitamins, and being mineral-rich it is the principal contributor to the ash figure by which flour is graded.

Answer: D

Correct answer: Lower ash content in the flour

Ash would rise, not fall. Without conditioning the bran is dry and brittle, so it shatters into fragments the same size as the semolina rather than peeling away in flakes, and those fragments carry their mineral matter into the flour. The other three - darker flour, shattered bran, poorer separation - are all consequences of the same failure.

Answer: A

Correct answer: Rittinger's law suits coarse crushing best

This is the false statement, and it inverts the usual assignment. Rittinger makes energy proportional to the new surface created, which is the dominant cost in fine grinding, so it suits the fine range. Kick’s law, depending only on the logarithm of the size ratio, suits coarse crushing, and Bond’s law with its square-root dependence sits between them.

Answer: B

Correct answer: The colour of the milled rice

Colour is a consequence of how far the bran has been removed, not a cause of breakage, so it cannot affect the head rice yield. The other three all can: whitening pressure applies the force that breaks weakened kernels, the drying rate determines whether fissures formed in the first place, and different hullers apply different amounts of stress in removing the husk.

Answer: C

Correct answer: It is carried out before grinding

Degermination precedes grinding, which is the whole point - the germ must be taken out intact before its oil can be spread through the meal. It is a maize operation rather than a rice one, and it removes the germ specifically; the pericarp is taken off separately as bran.

Answer: D

Correct answer: Energy scales with the surface created

Halving the particle size doubles the surface area, and it is the creation of new surface that consumes the energy, so the cost per tonne climbs steeply as the product gets finer. Rittinger’s law states this directly, and it is why the last stage of grinding often costs more than all the earlier stages together.