Oil Extraction and Processing Questions and Answers

Answer: C

Correct answer: Only three

The first three are right. A ghani is the traditional batch mortar-and-pestle press, worked slowly; a screw press compresses the material continuously against an adjustable choke; and solvent extraction takes the residual oil below one per cent.

The fourth is wrong and contradicts the third. A screw press leaves 5 to 8 per cent oil in the cake, because compression cannot squeeze a cellular material dry. That difference is precisely why high-oil seeds are pre-pressed and then solvent extracted rather than pressed alone.

Answer: D

Correct answer: Only three

The first three place their streams correctly. Miscella is the oil-and-solvent solution leaving the extractor, soapstock is the by-product of alkali neutralisation, and gums are what degumming removes.

The fourth is wrong. Spent earth is the used adsorbent from bleaching, filtered off with the pigments and metals it has taken up. Deodorisation produces a distillate instead - a stream rich in free fatty acids, sterols and tocopherols, and valuable enough to be recovered rather than discarded.

Answer: A

Correct answer: Bleaching

Bleaching is a refining step. It follows extraction, treating the crude oil with activated earth to adsorb colour pigments, residual soaps and trace metals, which are then filtered out.

The other three all precede extraction and act on the seed rather than the oil: dehulling removes the hull, flaking ruptures the cells, and cooking thins the oil and sets the moisture. The division is worth keeping clear, since preparation is about making the oil accessible and refining is about making the extracted oil fit for use.

Answer: B

Correct answer: Bleaching earth

Bleaching earth is added to the oil, not taken from it. Activated clay is stirred in, adsorbs pigments, soaps and trace metals, and is then filtered off as spent earth carrying the impurities with it.

The other three are removed: phospholipids in degumming, free fatty acids in neutralisation or physical refining, and waxes in winterisation. Some oil is lost with the spent earth, typically 20 to 30 per cent of the earth's own weight, which is why the dose is kept to what the colour specification actually requires.

Answer: C

Correct answer: Free fatty acid value

Free fatty acids come from hydrolysis - water splitting the triglyceride, usually with lipase catalysing it - so their level records hydrolytic deterioration.

The other three all belong to the oxidative pathway. Peroxide value measures the hydroperoxides of primary oxidation, anisidine value the aldehydes of secondary oxidation, and the rancid aldehyde odour is those secondary products reaching the nose. The two pathways are independent: an oil can be high in free fatty acids yet barely oxidised, or freshly pressed and already oxidising.

Answer: D

Fines block percolation and slow the extractor badly, so there is a limit below which thinner flakes stop helping. The other three all improve either the driving force or the condition of the material presented to the solvent.

Answer: A

Correct answer: Choke setting and cake thickness

The choke is the adjustable restriction at the discharge of a screw press, and setting it decides the pressure developed and hence the thickness and residual oil of the cake. It belongs entirely to mechanical pressing.

The other three are solvent plant concerns: hexane loss per tonne is a cost, a hazard and a regulated emission; fire and explosion precautions follow from hexane's flammability; and miscella concentration governs the load on the distillation train. No solvent is involved in pressing, and no choke exists in an extractor.

Answer: B

Fines pack down and destroy the permeability the bed depends on, and the extractor slows even though the flakes themselves extract quickly. Opening the flaking rolls slightly usually restores the drainage without much loss of yield.

Answer: C

A refining factor near unity would mean only the free acid was removed, and anything much above it means neutral oil is being saponified or entrained. Alkali strength, temperature and mixing are the usual places to look.

Answer: D

Correct answer: Lipase released at milling has acted

Eight per cent free fatty acid in three days is the signature of enzymatic hydrolysis, and rice bran is the classic case. Milling ruptures the cells and brings a very active lipase into contact with the oil, after which acidity rises by several per cent a day.

Oxidation would show as a rising peroxide value and a rancid odour, not as acidity, and neither moisture pickup nor wax crystallisation produces free fatty acids. The commercial consequence is severe: at 8 per cent the refining loss makes food use marginal, which is why bran is stabilised by heat or extracted at once.