which revolves a heavy stone wheel on an axle, one end of which is attached to and works on a pin or pivot set in the center of the trough. This mill wheel crushes and grinds as it rolls over the olives, which are constantly pushed by a scraper into its path. This may be worked by hand, by horses, or oxen, by steam or water power. The stone should be non porous lest it absorb oil which may become rancid.
The size of the crusher will vary with the needs of a given mill. Presses are of various kinds. The Italians, Spaniards and French generally use a screw press (descending.) This may be worked by hand, by horse or ox power, by water or steam. In any case the pomace is put into sacks of jute called "bruscole," which are then piled up, eight, ten, or a dozen high, or into a steel cage with or without crash to contain it, and placed under the descending screw of the press.
Mr. Cooper uses a beam press such as is used in cider making. The pomace is held in place by wooden crates and Russian crash. He suggests the oleomargarine press as probably the best for olive oil expression. In both Italy and Spain powerful hydraulic presses are used either with the jute sacks or the iron cage. They are similar to the hydraulic presses of the wineries, and in fact these latter can be used for oil extraction.
The objection to the hydraulic press is, that with it one runs the risk of suddenly applying too great pressure and what is needed in expressing olive oil is not sudden, but gentle and constantly increasing pressure. If the pomace of olives is suddenly subjected to extreme pressure, no oil at all will flow; for this reason hydraulic presses have been altogether abandoned in some parts of Spain, as in ignorant hands they did not give satisfactory results. The great advantage of the beam press is, that it is impossible to apply the pressure in any other way but by a steady and gentle increase, as more weight is placed on the end of the beam. But after all, in intelligent hands the hydraulic press is preferable, for if it is
