Why is it that you can smell the Jello when add powder to water but disappears?

When you add Jello powder to water, the powder particles disperse throughout the liquid and release their aroma. This is why you can smell the Jello at this stage. However, as the Jello mixture sits and begins to set, the powder particles become trapped within the gelatin network and the aroma molecules are no longer able to escape into the air. This is why the smell of the Jello gradually disappears.