136 Bulletin 135, Utilization of Cull Citrus Fruits

 Another serious mechanical problem was met in attempting
to clarify the juice. Citrus fruit juices contain large quantities
of gelatinous material in suspension, and this material effec-
tually closes up the pores of any ordinary filtering medium, so
that filtration is entirely too slow for commercial purposes. A
great variety of filters, including power-driven presses, was
used but'the results were not satisfactory.
 When the juice was poured on an ordinary filter of paper, cloth, or
brewers' mass, a small amount ran thru rapidly at first, but the rate rapidly
diminished with corresponding increase in clearness of the filtrate. Suction
increased the speed to some extent, but not enough to make the method prac-
ticable on a large scale. Filters of sand and fuller's earth yielded almost
water-clear filtrates but the rate was very slow. The same was true to a
greater or less extent of Norton Alundum, Tripoli stone, Berkfeld and Pukal
filters. The best results with suction filters were obtained by using a mat oI
sand mixed with asbestos fiber supported on cloth. With this arrangement
filtration could be hastened by occasionally stirring up the surface of the nma
 Filter-press filtration was next tried, using a small press and a pr'es'uIre
of 150 to 200 lbs. per square inch. But all the filteiing media tried-pape i
cloth, and brewers' mass-.promptly clogged and stopped the flow.
 Clarification of the juice by fi, it .,l I.. also proved un-
satisfactory. Centrifugal filtration, however, seemed to offer
a possible solution of the problem. After some preliminary lab-
oratory experiments it was found that a fairly satisfactory cl;tr-
ification could be effected by using a combined centrifu,(n
clarifier and filter of the DeLaval type. On account of the large
amount of suspended solids, it is recommended that the juice
first be put thru a simple centrifugal clarifying bowl (which
consists of one of the combined clarifiers and filters with the
filtering mechanism omitted) which will remove the greater
part of the suspension. For continuous working, two machines
would have to be provided, one being used as a simple clal i;f ;,
bowl while its filtering material was being removed and washed;
thus each machine would serve alternately as simple clarifier
and as combined clarifier and filter.
 Since the original work was done, a type of very high speed
centrifuge has been placed on the market, which, it is said, can
be used with satisfactory results on citrus fruit juices, yielding
a nearly clear product.
 In order to obtain commercial quantities of perfectly clear
juice it seems necessary to resort to the practice used in wine
manufacture-that is, storage until the solids settle out. This
would involve considerable expense for storage vessels and a
long delay (at least 6 weeks).