Youth is a type of Elvin beverage that was the root of the legend of the Fountain of Youth. It comes in a clear bottle with no markings other than a label saying: Youth in a Bottle. It is described to taste refreshing and also slightly sweet. It is served cold usually, as shown in its description in Book 1: Keeper of the Lost Cities. It consists of enzymes necessary for Elvin health.
When Sophie first met Elwin, he prescribed her a double portion of this nutrient because she had been deprived of it for very long. It can be noticed that she drank both bottles in two gulps. Elwin also prescribes extra bottles when Sophie is severely injured.
Despite the fact that elves should drink one per day, they are infrequently mentioned, and there was once a half drank bottle in Jolie’s Bedroom.