Olea europaea

Olive

A tree cultivated for its fruit, from which an edible oil can be extracted. There are numerous varieties with fruits varying from round to oval and from 1 to 3 cm in diameter. Under the thin skin is the fleshy mesocarp containing the oil and in the centre a black hard nut with a kernel. 

The fruits can be processed in several ways, each producing a different type of oilcake. Most commonly the whole fruits are crushed and pressed, first under low pressure and after that in another press under greater pressure, to produce a very hard cake consisting of kernels, broken kernels and pulp with a water content of 20-25% and a residual oil content of 8-16%. The cake is sometimes used as animal feed or is processed further by three methods. (1) The whole cake is solvent extracted. (2) The cake is recrushed, extracted with hot water and pressed. (3) The kernels and the pulp are separated either in a specially designed classifier or by flotation in water. The kernels, being heavier, sink to the bottom, while the pulp remains afloat. The floating pulp is 20-25% oil and can be used directly as livestock feed or can be further extracted. The kernels contain so little oil that they are discarded. If separated in a classifier, the skins (epicarp) can be collected separately from the kernels and the pulp. 

Another method (the Acapulco method) separates the fruits into kernels and pulp, and the oil is pressed out of the pulp between rubber discs. 

USE. Because of the rather low price at which the press cake is sold to factories for further oil extraction, there have been several investigations to assess its value in animal feeding. As the cake turns rancid rather quickly and may become completely unpalatable and even harmful to animals, it must be preserved either by drying or ensiling. Press cake containing kernels has a very low feed value and causes digestive troubles, especially in cattle. Therefore, the cake should be separated into kernels and pulp. The kernels can then be used as fuel to dry the pulp. The main value or the pulp as an animal feed is its high fat content. Owing to a peculiarity of the pulp, its protein is very low in digestibility. Contrary to what might be expected, the high oil content of the pulp has no adverse effect on the fat composition of the carcass. Up to 50% of the ruminant ration can consist of destoned press cakes and up to 15% does not decrease the digestibility of the ration. Calves can be fed 1-2 kg daily, fattening swine 0.8-1.5 kg and sheep 0.2-0.3 kg. Olive cakes extracted with solvents have less feed value because of their lower fat content. (The feed value of olive cakes is comparable to that of wheat straw.) The factor causing the decrease in digestibility seems to be soluble in tetrachloroethylene, as oilcakes extracted with this and subjected to alkaline hydrolysis showed no reduction in digestibility. Oilcakes so processed are comparable to good forage in feed value. 

The destoned cake has also been used in feeding pigs in proportions up to 50% of a daily ration consisting of maize, wheat pollards and coconut cake. No digestive trouble or decrease in appetite was observed, and the rate of increase in liveweight was normal; however, the feed efficiency tended to be somewhat lower. Cakes should not be fed to pregnant animals as the birth weight tends to be lower. The cake has a rather low palatability.