Custard Apples

January 8, 1997

This fall a testing program was undertaken which at first had exciting possibilities. We were contacted by a waste energy firm, Bartow Ethanol, in regards to pressing custard apples.

Custard apples are a fruit that looks somewhat like a green apple. The inside is almost entirely filled with large seeds, each growing from the core to the outer skin. The fruit is harvested in Australia for commercial purposes, and the sugar content is known to be satisfactory.

Another variety of this fruit grows wild on land on the southern shores of Lake Okeechobee here in Florida. The trees are on public lands and they serve some erosion control purposes.

The idea was to harvest these custard apples and press them to extract the juice. Because of the sugar content, it was felt that the juice could be fermented for the production of alcohol. One advantage was that the trees bear fruit at only three to five years of age.

A pilot plan called for harvesting the fruit with prison labor. A Vincent screw press, driven by a diesel engine, would be used in the field to squeeze the juice, thus minimizing transportation costs and solving the problem of press cake disposal.

Initial tests were conducted in Tampa. The fruit, shredded in an angle Disintegrator, was run through a screw press. The yield was approximately one gallon of press liquor per sixteen pounds of apples. The press liquor had a great deal of suspended solids; it looked like apple sauce. Nevertheless the separation achieved was quite adequate for preparing juice for the digester.

Tests included adding an enzyme to the fruit. Thirty five minutes after adding the enzyme the mass became pulpy and was readily pressed. The seeds came out whole (that is, not broken open) using this procedure.

Unfortunately it turned out that the Brix value (sugar content) of the juice never exceeded 4-1/2º, whereas the Australian variety runs 12º. The lower Florida content was not adequate or proper for fermentation, so the project has been abandoned.

Issue 54