I have a child with a restricted diet that can have no added sugar or other form of sweetener, with the exception of fruit juice. He is in desperate need of cough drops or throat lozenges, but I find they simply don't exist without some form of added sweetener in them. My idea was to craft a hard candy with just fruit juice as sweetener, and then just add menthol or something similar for soothing cough/throat. But I also can't find any recipes for hard candy using only fruit juice as a sweetener. Is it because the sugar or corn syrup, etc is needed to make the candy hard?? Is what I am trying to do even possible?
I think classic hard candy would be difficult if not impossible to make with fruit juice because it combines the fruit sugars (fructose) with a lot of other things, and hard candy is normally made by heating sucrose (table sugar, which is 50% fructose, 50% glucose) to the hard-crack stage (300-310F) to the point where it is essentially 99% sugar. As the sucrose heats it hydrolyzes into glucose and fructose which changes the structure.
Pure fructose does not behave the same way as sucrose. I think you need some glucose to get it to form into a hard candy. (You can also make hard candy from sugar and high fructose corn syrup instead of from table sugar.)
Additionally, fruit juice isn't pure fructose to begin with and the other things in the juice would cause problems with the process and would probably scorch.
I think the idea given in the comments of trying for a gummy or a syrup will work better.