SEPTEMBER 25, 2013
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 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.”