Milling of Cereals Questions and Answers

Answer: A

Correct answer: Pericarp

The pericarp is the outermost layer of a cereal grain - the fruit coat, derived from the ovary wall - and it is what the miller removes first, as bran.

Working inward from it lie the seed coat, then the aleurone layer, a single layer of protein- and mineral-rich cells, and finally the starchy endosperm that forms the bulk of the kernel and yields the flour. The germ, the embryo, sits at one end. The pericarp is tough and fibrous, which is what makes conditioning worthwhile: damp bran peels away instead of shattering into the flour.

Answer: B

Correct answer: Starchy endosperm

The starchy endosperm forms the bulk of the kernel - roughly 83 per cent of a wheat grain - and is the food reserve for the embryo, consisting of starch granules embedded in a protein matrix. Milling exists to separate it cleanly from everything around it, and it is what becomes white flour or white rice.

The pericarp and seed coat become bran, the germ an oil-rich by-product removed to protect shelf life, and the aleurone layer, though rich in protein and minerals, adheres to the bran and mostly leaves with it.

Answer: C

Correct answer: Its oil turns rancid in storage

The germ is rich in oil - around 10 per cent in wheat and considerably more in maize - and that oil oxidises and hydrolyses in storage, giving flour a rancid flavour and a short shelf life. Removing the germ is therefore a keeping-quality measure above all.

The irony is that the germ carries much of the grain's vitamin E, B vitamins and protein, so what is removed for shelf life is nutritionally valuable. It is recovered as a by-product and sold for oil extraction or as a food supplement rather than discarded.

Answer: D

Correct answer: The proportion of whole kernels

Head rice yield is the proportion of the paddy that emerges as whole, unbroken kernels, and it is the measure that determines a mill's revenue. Whole grains command a substantially higher price than brokens - often nearly double - so a few points of head rice yield are worth far more than the same quantity of total output.

Total milled rice from paddy is a different figure, the milling yield, and it includes brokens. Degree of milling describes how much bran has been removed, and husk removal is what hulling achieves.

Answer: A

Correct answer: The husk from the paddy grain

Hulling is the first operation of a rice mill: it strips the husk, or hull, from the paddy grain to leave brown rice. The husk is about 20 to 22 per cent of the paddy's weight, is highly siliceous and inedible, and is used as fuel, in board manufacture or as a source of silica.

What follows is whitening, which removes the bran layers and germ from the brown rice, then polishing and grading. Hulling and whitening are distinct operations on different layers, and confusing them is the commonest error here.

Answer: B

Correct answer: Passing paddy between rolls of unequal speed

A rubber roll huller passes the paddy between two rubber-covered rolls turning in opposite directions at different speeds. The speed differential shears the husk open and strips it away, while the rubber surface cushions the kernel.

That gentleness is the point: compared with the older disc sheller, which abrades the grain between emery-coated discs, the rubber roll causes far less breakage and gives a markedly better head rice yield. The cost is roll wear, since the rubber is consumed and must be replaced regularly.

Answer: C

Correct answer: Unhulled paddy from brown rice

Hulling is never complete in one pass - a proportion of grains escape the rolls unhulled - so the discharge is a mixture of brown rice and paddy. The paddy separator divides the two, using their difference in density and surface texture on an oscillating tray or compartment separator, and returns the unhulled grains to the huller.

Separating them matters because paddy passing into the whitening machine would be abraded pointlessly, wearing the equipment and producing brokens. Bran removal is whitening's job, and broken separation is grading's.

Answer: D

Abrasive or friction whiteners scour the outer layers away, and the degree of whitening is expressed as the degree of milling. Over-milling costs both yield and nutrition while under-milling leaves a product that keeps badly.

Answer: A

Correct answer: Improve appearance and gloss

Polishing follows whitening and removes only the last traces of bran and the fine flour adhering to the kernel, giving a smooth, glossy surface. Its purpose is appearance and market acceptance rather than the removal of any substantial layer.

Whitening is the operation that actually removes the bran and germ, and it is the one that determines the degree of milling. Polishing is done with a gentler abrasive or with a water mist, since by this stage further aggressive treatment would only break kernels.

Answer: B

Correct answer: Adding water and resting the grain

Conditioning, or tempering, means adding a measured quantity of water to the wheat and resting it - for a few hours in soft wheat, up to a day or more in hard - so that the moisture penetrates and equilibrates.

Two things follow. The bran absorbs water, becoming tough and leathery so it peels away in flakes rather than shattering into the flour; and the endosperm mellows, so it breaks up more readily with less power. Both effects raise flour purity and lower energy consumption, which is why no mill runs without it.