During juice recovery, finishers separate pulp from juice stream; pulp still contains some juice that it is possible to recover with a ater extraction process. Juice and soluble solids so recovered are called Pulp Wash o WESFS (Water Extracted Soluble Fruit Solids). It is used a countercurrent systems, usually with three or four stages. Every stage consists of a mixing unit (a screw conveyor or a small tank with stirrer) and a finisher.
Pulp
in is in the first stage and pulp out is at fourth stage. Water in is at the
fourth stage and water out is at the first stage as strong liquor (pulp
wash) whose soluble solids concentration depends from process parameters; for
orange it is, usually, ranging from 4 to 7°Bx. Pulp wash is, then, concentrated
alone or with the juice.
Pulp wash chemical composition is close to the juice the main
difference is pectin content that is higher: this increased content may cause
problems to evaporators operativity due to viscosity increase that may cause,
gelation, and a "cooked" taste of concentrate. To solve the problem
are currently used pectolitic enzymes. These products acts decreasing pectic
chains length and are pectinases and /or pectinlyases.
For many years pulp wash addition to orange juice has been forbidden and a lot of analytical chemistry work has been done to detect it into the juice.
Recently, and with the limit to in-line pulp wash only, this addition has been accepted with the clause that it cannot represent more than 10 % of total soluble solids of the product.
Only NFC (not from concentrate) juices cannot contain pulp wash.
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