Milling of Cereals Questions and Answers

Answer: C

Correct answer: 0.325

The ash ratio compares the flour's ash with the wheat's:

\[ \frac{0.52}{1.60} = 0.325 \]

A low ratio means the mill has separated the endosperm cleanly, leaving most of the mineral-rich bran and aleurone in the offal. The figure is a better index of milling performance than the flour ash alone, because it removes the effect of the wheat's own ash content, which varies with variety and growing conditions.

Answer: D

Correct answer: 12 kWh per tonne

Specific energy consumption is the power drawn divided by the throughput:

\[ \frac{60\ \mathrm{kW}}{5\ \mathrm{t/h}} = 12\ \mathrm{kWh\ per\ tonne} \]

The units work out because kilowatts divided by tonnes per hour give kilowatt-hours per tonne directly. Expressed this way the figure is comparable between mills of different size, and it allows the energy cost per tonne of paddy to be set against the value of the rice and the brokens.

Answer: A

Correct answer: 11.0 per cent

Germ yield is the germ recovered as a percentage of the maize treated:

\[ \frac{220}{2000} \times 100 = 11.0\ \mathrm{per\ cent} \]

This is close to the germ's natural share of the maize kernel, so the degerminator is recovering nearly all of it - which is the object, both to protect the shelf life of the grits and to capture the germ for oil extraction. A low yield would mean germ left in the endosperm fraction, taking its oil with it.

Answer: B

Correct answer: 15.4 currency units

The seven percentage points move from brokens to head rice, and each tonne gains the price difference on that fraction:

\[ \Delta = 0.07 \times (480 - 260) = 0.07 \times 220 = 15.4 \]

The calculation shows why head rice yield dominates a rice mill's economics. Total output is unchanged - the same rice leaves the mill - but its composition has shifted towards the premium grade, and on tens of thousands of tonnes a year that difference is what separates a profitable mill from a marginal one.

Answer: C

Correct answer: Both Statement I and Statement II are correct

Both statements are correct and the second explains the first. Conditioning adds a measured quantity of water and rests the wheat so the moisture penetrates the outer layers.

Damp bran becomes tough and leathery, so at the break rolls it peels away in flakes that sieves and purifiers can remove cleanly, instead of shattering into fine specks that pass into the flour and raise its ash. The endosperm meanwhile mellows and breaks up with less power, so conditioning improves purity and energy consumption together.

Answer: D

Correct answer: Statement I is incorrect but Statement II is correct

Statement I is incorrect on both counts: break rolls are fluted, not smooth, and they run at a substantial speed differential - commonly around 2.5 to 1 or more.

Statement II is correct and explains why. The differential creates a shearing action between the two surfaces, which opens the kernel and scrapes the endosperm away from the bran without pulverising the bran into the flour. Smooth rolls at low differential describe the reduction rolls, whose job is to crush endosperm particles gradually into flour.

Answer: A

Correct answer: Both Statement I and Statement II are correct

Both statements are correct and the second explains the first. A purifier passes the stock over an oscillating sieve while air is drawn upward through it, so particles are sorted by terminal velocity as well as by aperture.

That matters because a flake of bran and a granule of endosperm may pass the same sieve while differing greatly in density: the light flake is lifted by the air current and carried off, while the dense endosperm particle falls through. Sieving alone could not separate them, which is why purifiers sit between the break and reduction systems.

Answer: B

The reason is correct and it undermines the assertion: a great deal of the damage is already present when the paddy arrives. Careful drying at the intake protects head rice yield far more effectively than any mill adjustment can.

Answer: C

Correct answer: Both Statement I and Statement II are correct

Both statements are correct and the second explains the first. A rubber roll huller passes the paddy between two rubber-covered rolls running at different speeds, so the husk is sheared open and stripped away while the resilient surface cushions the kernel.

A disc sheller instead abrades the grain between emery-coated discs, which cracks kernels already weakened by drying stresses. The rubber roll's gentler action gives a markedly higher head rice yield, and since whole grains fetch nearly twice the price of brokens, that advantage outweighs the cost of replacing worn rolls.

Answer: D

Correct answer: Both Statement I and Statement II are correct

Both statements are correct and the second explains the first. Raising the extraction rate means taking flour from further out in the kernel, so material from the aleurone layer and the inner bran passes into the flour.

Those layers are pigmented and mineral-rich, so the flour darkens and its ash content rises together - which is precisely why ash is used as the trading index of extraction. The trade-off runs the other way nutritionally: higher extraction retains more of the fibre, minerals and B vitamins that low-extraction white flour discards.