Pistachio Nuts

February 1, 2005

Pistachio processors in California operate during a short harvest season, from September into October. The green berries, as harvested, are about the size of an olive. At the processing plant, an exterior layer of pulp is removed. This is done in abrasive peelers, with water. Once the rejects (immature and hollow seeds) are removed, the pistachios are dried, usually in GSI dryers. The product that comes out is the snack we are familiar with: a white shell, cracked opened by the heat, containing a delicious nut.

Setton Pistachio in Terra Bella is a very large processor. They use three Vincent KP-16 screw presses to separate the waste pulp from peeler water. The dewatered pulp is given to farmers for blending as a cattle feed.

Setton processes 120 tons per hour of green berries. About one third of this weight, 40 tph, is pulp that surrounded the shell. Most of the time two KP-16's can handle the load, giving the KP-16 a maximum rating of 20 tph of pulp.

Static screens are used ahead of the KP presses. These separate large quantities of water. This is effective in pre-thickening the flow to the presses. The solids from the screw press come out as a thick, fibrous mass. The rotating cone feature of the KP presses is not necessary at all.

Smaller scale pistachio operations might drain the pulp in static screens and then haul the soggy pulp for landspreading with a manure spreader. Others pump the wastewater flow with the pulp into a settling pond; between harvests, the dried ponds are emptied with excavators.

Issue 157