The great prune juice mystery

Over the weekend, a friend [thanks, L!] offered me a prune. I can honestly say that I don’t remember ever having eaten one previously, so I decided to give it a try. I didn’t love it, but I didn’t hate it either, which is about par for the course when it comes to my reactions to most dried fruit. We somehow got to talking about how in the world prune juice gets made. After all, since a prune is a dried plum, can there actually be much juice left to squeeze from it? Not really, it turns out.

Image from a Sunsweet romotional booklet dating from 1942. Via Flickr user alsis 35 (now at ipernity), used under a Creative Commons license (CC BY-NC 2.0)

Image from a Sunsweet promotional booklet dating from 1942. Via Flickr user alsis 35 (now at ipernity), used under a Creative Commons license (CC BY-NC 2.0)

As detailed by Laszlo P. Somogyi in the 1992 specialty publication Processing Fruits,

Prune juice prepared from California dried prunes has been produced commercially since 1934 and consumed in substantial quantities in the United States (Woodroof, 1974). Currently, it is not a popular beverage outside of the United States…. [Does he mean to suggest that it’s actually a “popular” beverage here?]

Prune juice differs from other fruit beverages in that it is a water extract of dried fruit, rather than squeezing of fresh produce (Loh, 1980).

Essentially, the dried plums are rehydrated/cooked with boiling water. As Somogyi explains, “from the disintegrated fruit, the juice is separated, either by pressing the pulp in a hydraulic press or by high-speed centrifugation…. The extract is then clarified [through settling, siphoning, or filtering]…. The resulting extract … is collected in surge tanks and concentrated by heat….”

The FDA specifies what can legally constitute prune juice. In part, the rules note that “Canned prune juice is the food prepared from a water extract of dried prunes and contains not less than 18.5 percent by weight of water-soluble solids extracted from dried prunes.” The USDA similarly details [PDF] the “salient characterstics” of “juice, prune, canned,” specifying that “the canned prune juice shall be prepared from a water extract from properly dried, matured, sound, wholesome, whole prunes” and that “flavoring ingredients such as lemon juice, lime juice and citric acid, or combination of either one may be added. The canned prune juice may also contain honey and be fortified with ascorbic acid.” Why the so-called flavoring ingredients? In the November 1948 issue of California Agriculture, famed California food scientist W. V. Cruess notes [PDF] that “The addition of about 0.2% of citric acid greatly improved the juice, for most of those who tasted the juices.”

Reportedly, the expense of producing the dried fruit extract is high enough that “there is an economic incentive for adulteration of prune juice with less expensive fruit juices, fruit juice concentrates, and/or sugar syrups” by less-than-scrupulous producers; as a result, in the 1990s researchers in the Department of Pomology at UC-Davis devised chemical analyses “for establishing the authenticity of prune juice.” [PDF]

Alas, the popularity of prune juice as a natural remedy for constipation eventually led to a negative view of prunes among much of the American populace. As a result, the California Dried Plum Board (CDPB) explains that

In 2000, the Food and Drug Administration granted the California Prune Board permission to use “dried plums” as an alternative name to prunes.  Why the name change?  Because 90% of consumers told us that they’d be more likely to enjoy the fruit if it were called a dried plum instead of a prune.

Prune juice didn’t get rechristened, though. As a story from ABC News explained back in 2000, “Prune juice will still be prune juice, however. Dried fruit juice would be a contradiction in terms, the industry was told by the Food and Drug Administration.” Ya think?

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