Our protagonist lives on one of a group of remote islands where she makes her living harvesting a peculiar fruit. The edible part grows in the middle of liquid-filled sacks that hang near the top of the local trees. The top of the sack must be pinched and sealed before being cut from the tree because the fruit is spoiled by the reaction the liquid in the sack has when exposed to air. However, when properly harvested and treated, the end result is singularly delicious.
The trunk of the tree is flexible, downright bendy even, but quite weak. The weight of the average adult attempting to climb the tree is enough to snap it in half, which also spoils the fruit. (I imagine that the trunk is hollow and that some sort of vein connects the sacks to the roots, but any explanation is fine.)
What would explain these features?
Most importantly, what kind of liquid could fill the sacks, why does it react with the air, and how do the villagers process it to extract the fruit?
You may assume whatever you want regarding the islands and the type of plant this “tree” really is (perhaps it’s more aptly classified as a flower, for example, or its roots extend into the ocean—anything goes.) Processing the fruit could mean anything including freezing it, injecting another liquid into the sack, opening it while submerged in another liquid, etc.