Question

Hello, honorable Rabbi,
Something is unclear to me regarding rich matzah. On the one hand, our Sages say that fruit juice does not cause leavening; on the other hand, it is known that fruit juice contains water in some concentration or another, depending on the fruit.
Seemingly, any contact with water causes the flour to become leavened, so what is happening here?
What am I missing?
Thank you very much.