Olive Oil Extraction By-Product Uses Waste Cake

I know you can’t eat it, but can it be fed to livestock and it is nutritious? Does it need any further processing prior to being used for feed? Can it be put around olive trees as a mulch? What other uses does it have?

The olive cake is one of the by-products that is generated when processing olive oil. The physical composition of the olive is skin, pulp, the stonewall and the kernel. Through all of this physical matter is the water and oil which are mostly extracted from the olive during processing. After going through the extraction process about 35% of the fruit will be left as olive cake. In 1985 when it was estimated that olive cake production worldwide was nearly 3 million tonnes.

Olive Mill Waste: Orujo
Exhausted olive pulp (orujo) from busy olive oil mill factory being conveyed into huge metal silo container for later composting.

The most common use for olive cake is in heating. Because of the small amounts of olive oil still in the cake, when dried, it burns very well in fireplaces and heating furnaces. It is very common in the traditional press type oil factories to see people shovelling dry cake into furnaces to warm water for the oil extraction process. In addition to this, it keeps the room warm while they work through autumn into winter.

The olive cake is generally pressed into briquettes for commercial sale for fireplaces or is left in its ‘mat-like’ state for furnace heating inside the factory.

This article cannot go into all details on the various types of olive cake and feed preparation methods, however, it does give evidence that research has been and is being done into the cake’s possible uses.

The olive cake is relatively high in moisture, about 24%, and oil, about 9%. (The amount of oil left in the cake will depend on the efficiency of the milling equipment and the skill of the operator.) These two components cause rapid spoilage of the olive cake material when it is exposed to the air.

Early Italian data states that the main problem with the olive cake that has been obtained by centrifugation is the rapid spoilage time, perhaps as short as 4 or 5 days. The same research concludes by saying “Olive cake as such is not very palatable and it is not widely consumed.”

A recent Australian analysis of olive cake comes to much the same conclusion.  The composition of the cake was as follows:

  • Moisture  28%
  • Dry Matter 71.5%
  • Crude Protein 2.3% of dry matter
  • Digestibility 25.3% digestible dry matter
  • Metabolised Energy .6 MJ/kg dry matter

“Both the energy and protein content of this material are extremely low, and it would have little if any value as a feed for any class of livestock”.

As a comparison, mixed pasture hay has an average crude protein, and has a %of dry matter of 11% and a Metabolisable energy of 8MJ/kg dry matter. A 40 kg dry sheep on a maintenance ration would require 8% crude protein and 6.5MJ/day of Metabolisable energy.

A study of olive cake is a stock feed in Tunisia concluded that “olive cake, when mixed with molasses in a ration feed mix, is palatable to livestock but distributed by itself it is not palatable, causes weight loss and is poorly digested”.  The higher the percentage of olive cake in the feed ration, the greater the weight loss occurred by the livestock.

Because of the seasonal timing of production, availability of olive cake is limited to certain periods of the year. People wanting to use it as a feed supplement or base would need to take its availability and storage capacity into account.

It would appear that from the available research, olive cake in its raw by-product form is currently of limited value as a feed source for livestock.

Some conclusions from the FAO book “Olive By-Products for Animal Feed” (1985) follow:

“As for the use as animal feed, detailed recommendations which could apply to all countries cannot be made. However, it is possible to recommend the general use of olive by-products (leaves and olive cake in all forms) bearing in mind that these by-products should be considered as crude lignocellulose feed comparable to cereal straw or a poor quality hay.”

“In cases of shortage periods, all types of olive cake can be recommended in survival rations, although none of them can make intensive production possible. Depending on the type of olive cake, it is possible to ensure maintenance of the animals or a moderate production level. However, it is preferable to incorporate 8-10% molasses to facilitate olive cake consumption.”

“… partially destoning olive cake by screening or ventilation can be recommended. This is the most practical, simplest and most economic method at present and one of the most effective for improving the feed value of olive cake. It’s crude fibre content should then barely exceed 15% of dry matter.”

“Olive tree leaves and branches constitute a fodder of exceptionally high quality (which is higher as the proportion of wood is lower).  It is recommended that the leaves be used preferably fresh since their nutritive value is higher than that of the leaves which have been dried or preserved by ensilage.”

In the Mediterranean region, large companies buy the olive cake and extract the remaining olive oil using solvents. In time, companies in Australia will probably be set up to process olive cake in the same way. The Mediterranean companies are currently paying between 10 and 20 cents per kilogramme for olive cake. This figure varies depending on the type of oil extraction machinery in which the ways cake was produced. The solvent extracted oil is often blended with better quality oils prior to sale.

Another possible use for the cake is in the area of orchard mulch. As with any processing system, the ultimate aim is to distribute all by-products into either a sale-able product market or back into the existing system at some points.   Although some farmers have been using the olive cake for mulch for many years, little scientific research is available to present to determine the effects of this practice on the orchard.  More trials need to be done in this area.

Read more:  Olive Oil Extraction

Read more: Olive Oil Machinery

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