Oil Extraction and Processing Questions and Answers

Answer: A

Passing the seed between smooth rolls breaks the oil-bearing cells and produces a thin flake, so solvent or pressure has only a short distance to work over. Flake thickness of a quarter to a third of a millimetre is typical, and getting it wrong costs either yield or throughput.

Answer: B

Correct answer: Coagulate protein and thin the oil

Cooking does two things at once. Heat coagulates the protein of the cell walls, so the ruptured cells release their oil instead of holding it in a colloidal emulsion; and it lowers the oil's viscosity, so the freed oil drains or presses out readily.

Conditioning also adjusts the moisture to the value the press or extractor needs. It certainly does not raise free fatty acids - heat inactivates the lipase that would otherwise do so, which is a further benefit. Sterilisation is incidental, and hull removal is dehulling, an earlier and quite separate step.

Answer: C

Correct answer: Raise the oil content of the feed

Hulls carry very little oil, so removing them concentrates the oil in what remains - the feed to the press or extractor is richer, and the same plant handles more oil for the same throughput of material.

There is a second gain: hulls are absorbent and would retain oil during processing, so removing them reduces the loss in the cake as well as raising the yield. Free fatty acids are removed in neutralisation, colour in bleaching, and moisture is set during conditioning - all later steps with quite different purposes.

Answer: D

It works the seed slowly between a rotating pestle and a fixed mortar, and its low speed keeps the oil cool. Yields are low by modern standards but the oil is prized in some markets for its flavour and keeping quality.

Answer: A

The worm shaft reduces the volume available as the material advances, and the oil escapes through slots in the barrel while the cake leaves at the choke. Adjusting the choke changes the pressure and so the residual oil in the cake.

Answer: B

Correct answer: Around 5 to 8 per cent

A screw press works by compression, and compression alone cannot squeeze a cellular material dry. Typical expeller cake retains about 5 to 8 per cent oil, which is why pressing is often only the first stage.

Solvent extraction, which dissolves the oil rather than squeezing it, takes the residual below 1 per cent. That is exactly the reasoning behind pre-press solvent extraction for high-oil seeds: press out the bulk cheaply, then recover the remainder with solvent. A figure of 20 per cent would represent a badly set press rather than normal operation.

Answer: C

Commercial hexane dissolves triglycerides readily, boils at a convenient temperature and is easily recovered for reuse. Its flammability is the reason extraction plants are built with such stringent fire and explosion precautions.

Answer: D

Countercurrent stages bring the freshest solvent into contact with the most nearly exhausted flakes, which maximises the driving force at every point. Immersion extractors instead submerge the material completely and suit finer particles.

Answer: A

Correct answer: The oil and solvent mixture

Miscella is the solution of oil in solvent leaving the extractor, typically 25 to 30 per cent oil in hexane. It is sent to a distillation train where the solvent is evaporated for reuse and the crude oil recovered.

The other three name different streams: spent meal is the extracted flakes, which go to a desolventiser-toaster; gums are the phospholipids removed in degumming; and soapstock is the alkali-neutralisation by-product. Keeping the streams distinct is worth doing, since each has its own recovery route and its own value.

Answer: B

Steam sparging drives off the hexane while the heat inactivates trypsin inhibitors and other antinutritional factors. Over-toasting damages lysine, so the operation is a balance rather than simply a matter of heating hard.