This section is from the book "The Steward's Handbook And Guide To Party Catering", by Jessup Whitehead. Also available from Amazon: Larousse Gastronomique.
Olive oil is obtained by crushing and pressing the olives in sacks, it is then subjected to refining processes. A vast quantity is produced yearly in the old countries and California is contributing largely to the supply, which she usuallv ships in cans; so it is not difficult, as is sometimes represented, to obtain real olive oil; but there is a likelihood that imitation oil being refined cotton oil, or pea-nut or both mixed, may be put upon the unwary purchaser at the price of pure olive. The best test is heating some of the oil in a frying pan, letting it become hot enough to smoke, then if the experimenter have had experience with low grades cotton oil, he will detect sufficient of the same smell-in the refined article to apprise him that it is cotton oil still. Much cotton oil goes abroad in barrels and comes back in flasks labelled pure olive oil. The probability is in most cases it is a mixture of real olive with pea-nut oil and double-refined cotton seed. As only the thoroughly educated palate ran detect the difference there is no particular harm in this but the making the consumer pay for a cheaper imitation the high price of the genuine article.
Salad oil is one of the items of serious expense in hotels and restaurants and the subject is worthy of thought and attention.