Rebbe,
The Gemara discusses fruits which it's not the derech to squeeze. Only the squeezing of grapes and olives are real d'Orayta type issurim because they are meant to be squeezed and turned into wine and olive oil.
In our days, however, fruit that wasn't meant to be squeezed in Chazal's days such as plums and beets are massed processed as juice. Beets are used to make borscht and plums are used in prune juice and even sloe gin fizz. Chazal probably didn't have oranges or grapefruits. Oranges originally come from China and India and we don't find a word for them (then) or evidence that they had them in Eretz Yisroel or Bavel in ancient times. Orange juice is a major industry today.
Would this change in metziyus make squeezing these fruits into a d'Oraysa in our day?
Kesiva v'chasima tova and shana tova
Sam Kosofsky
Dear Sam,
You asked a good question.
Fruits that are sometimes squeezed in our days are at least Asur m'Drabanan. Some say oranges, etc. would be d'Oraysa in our day, since it is now the Derech to squeeze them. (See for example Rashi Shabbos 145a which begins "Dvar Torah").
However, there are those who say that only olives and grapes are d'Oraysa since only wine and oil are called true fluid (Mashke). See Shmiras Shabbos K'Hilchoso chapter 5 footnote 15, and Orchos Shabbos of Rav Gelber and Rav Rubin 4:10-12 and footnote 17 at length.
All the best
Reuven Weiner