(Rev. Dec. 2011)
The popularity of pomegranate juice has risen dramatically in Europe and North America. This demand arises at least partly from the medical benefits of the anti-oxidants present in the juice.
In one test, a large number of commercial juices were acquired at local markets. Large differences in color, suspended solids, and, especially, flavors were noted. Overall, the juice tastes somewhat like bitter cranberry juice. It is apparent that the flavor is affected adversely by the presence of tannin in the juice.
A pomegranate is a very round fruit, about the size of an orange. It has a hard, red outside skin. Inside are arils that grow attached to either a thin membrane or a pulpy mass of yellowish-white material.
The arils are a watery red color, about the size of half a pea. These arils are juice sacks with a tough outer membrane, containing a seed and a lot of juice. When the tough outer membrane is burst, juice flows freely. Juice yield of 90% was obtained when pressing arils. Overall, two-thirds of the weight of a pomegranate is made up of arils.
The juice from the arils of mature fruit is high Brix, up to 18o. The pH is very low, someplace between 2 and 4 pH.
The problem with pomegranate juice is separating the arils from the skin and white membrane. Bitter off-flavor is added to the juice by the tannin in the membrane. Hand picking the arils from the fruit is too slow a process to be commercially viable.
Investigation revealed a number of methods employed to separate arils. Tumbling the fruit in a machine like a grape destemmer reportedly works in India. In Georgia (ex-USSR) the fruit was lightly crushed and squeezed between rollers, prior to removing a patch of skin so that the juice could be expelled by hand squeezing. One juicer slices the fruit in half and then uses a hemispherical reamer, much like a Brown orange juice extractor. Similarly, the FMC orange juice extractor has been used, with limited results so far. In addition, experiments have been run with vibratory screens and flotation. (The arils sink but the membrane floats.)
A number of tests were run using the Vincent screw press. Everything from pure arils to whole fruit was fed into the press. The results, especially in terms of juice yield, were excellent.
It would appear that to produce consistent, high-quality juice, the use of debittering technology should be considered.