I think it's a definition issue. They like literal translations..which will be helpful to us down the line when you can differentiate between inside /within.בְּתוֹך an actual object or inside / within bifnim בפנים . (I'm just learning too, but I noticed the translating we would use colloquially isn't as helpful when learning vocab).
Is "et" not necessary here because "et" is ultimately a proposition, & we're swapping that preposition out for "betoch"? Put differently, do propositions like the ones we're learning in this unit make "et" unnecessary?
Cuz I feel like my brain keeps telling me the sentence should read "... בתוך את המיץ," even though I haven't seen anything structured like that before. Please help! And thanks in advance. :-)
Since בתוך המיץ is a prepositional phrase it doesn't need את in Israeli Hebrew. You raise an acute and interesting point that the roots of את are prepositional. If you want to read more about this topic in an advanced way, consult the Encyclopedia of Hebrew language and Linguistics or visit the website of the Academy of Hebrew Language.
I would say that the bottom line is that את is not needed here, because it is used ONLY before a definite direct object, and there is no DDO in this sentence.
Plus, whenever you have any preposition, את is not used, because other prepositions imply either an indirect object or a prepositional phrase.