May 20, 2016
A Vincent customer has built a successful business which produces avocado oil from distressed fruit. They process a couple hundred tons a day of windfall and packing house rejects, all black and soft.
The oil is extracted from the pulp, bottled, and sold as specialty cooking oil.
The process used is very similar to that used by producers of olive oil. The avocados are run through Italian 50 hp olive shredders and then fed into mixing tanks. GEA Westfalia describes this process as follows: "From there the flow goes to blanchers which stir the dough at 40/45 °C for one to two hours. Next it goes into a two phase decanter, separating oil+water and pomace."
The oil+water mixture is sent to bowl centrifuge to separate the oil. This oil is cold pressed extra virgin, and it does not need to be refined.
Recently we were contacted by our customer because the KP-10 screw press we supplied a few years ago is too small for their current project. The goal is to remove additional moisture from the decanter sludge (they call it Pasta). The press liquor will be used as feedstock for a biogas digester.
Normally a screw press cannot remove any additional moisture from decanter sludge. However mixing press aid into a sludge occasionally enables the screw press to separate a significant amount of press liquor. As with olive sludge, avocado Pasta requires a heavy dose of press aid, from 6% to 20% by weight. We ran tests on the avocado, comparing rice hulls to cellulose fiber (ground wood). It looked like the use of cellulose fiber let the press separate twice as much press liquor as the rice hulls.
We were pleasantly surprised to see that a layer of oil floated up from the press liquor. This points us toward the selection of a high toque Series CP press instead of the more economical Series KP machines. It remains to be seen if this oil is suitable for recovery.
The liquor showed a fuzzy 10 Brix on my refractometer, so it might be usable as a feedstock for a biogas digester.
Samples from one of our trials showed 68% moisture in the as-received Pasta, 62% moisture after addition of press aid, and 56% moisture in the press cake.
It is anticipated that the press cake can be used either as a biofuel or animal feed. The presence of fiber from the press aid might enhance value as animal feed.
GEA Westfalia did alert us that in avocado skin there can be a product that the literature has named "persin". It is poisonous to some animals but not human beings. Birds are especially sensitive to persin: try putting half an avocado in a cage with a bird inside. As soon as the bird eats some of the peel, it will die.
Separately, Anderson International of Cleveland, Ohio has been contacted to see if oil can be separated from the avocado stones with their Anderson Expeller®. To date no results are available.