Milling of Cereals Questions and Answers

Answer: C

Correct answer: Rittinger rises steepest and overtakes

At 2 mm Rittinger predicts the lowest of the three, but by 0.25 mm it predicts 45 kWh/t against Kick’s 22. Its energy is proportional to the new surface created, which goes as the reciprocal of particle size, so it climbs far faster than Kick’s logarithmic form as the product gets finer. This is exactly why Kick suits coarse crushing and Rittinger fine grinding.

Answer: D

Correct answer: Shear is needed to open the kernel

A differential means the two rolls turn at different speeds, so the material is torn rather than merely squeezed. That shearing action is what splits the kernel open and scrapes the endosperm off the bran without pulverising the bran itself. Reduction rolls have no bran to work around; they grind clean semolina, for which compression at nearly equal speeds is sufficient.

Answer: A

Correct answer: 8 per cent

Read across the four rows. Four per cent leaves the rice dull with poor keeping quality, so it is inadequate. Eight per cent achieves good appearance and good keeping at 92 per cent yield. Beyond that the extra whitening buys only a marginally whiter grain while the yield falls to 88 and then 84 per cent - a real loss of saleable rice for no gain in keeping quality.

Answer: B

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the mechanism, which works on the two tissues in opposite directions. Water toughens the bran so that it peels in flakes rather than shattering into the flour, and it makes the endosperm more friable so that it releases cleanly. That difference in response is exactly what allows the two to be separated, so tempering is not a preliminary but the basis of the whole process.

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason is the purpose. A differential of two and a half to four to one makes the faster roll tear past the slower, shearing the kernel open and scraping endosperm from the bran. Reduction rolls run at about 1.25 to 1 because they are grinding clean semolina, where compression suffices and shear would only produce excess fine flour and starch damage.

Answer: D

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason states the difficulty a purifier exists to solve. A sieve classifies by size alone, and a bran flake can be exactly the same size as a semolina granule. What differs is density and aerodynamic behaviour, so the purifier passes the stock over a sieve in a rising air current and lifts the light flakes away. Without it, low-ash flour at commercial extraction is not attainable.

Answer: A

Correct answer: A is false but R is true

The reason is true and it is precisely why the assertion fails. Most breakage originates in fissures formed during drying, before the paddy reaches the mill, and a fissured kernel will break under any pressure sufficient to remove the bran. Reducing whitening pressure limits further damage but cannot restore a yield that was lost at the drying yard.

Answer: B

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the whole justification. The maize germ is large and contains most of the kernel’s oil, which oxidises rapidly once ground and makes the meal rancid within weeks. Removing it before grinding both extends the shelf life of the meal and yields the germ intact as a valuable oil-bearing by-product.

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason is the mechanism. Rittinger makes energy proportional to the new surface created, and surface area goes as the reciprocal of particle size, so the predicted energy rises steeply as the product gets finer. Kick’s law depends only on the ratio of sizes and rises logarithmically, so the two diverge widely at fine sizes.

Answer: D

Correct answer: A is false but R is true

The reason is true and it is exactly why the assertion is false. Raising extraction pulls in fractions from nearer the bran, which are richer in mineral matter and darker, so ash rises and colour worsens - the grade falls rather than improves. What rises is the yield, and the miller trades one against the other.