[Muddy]

I'm trying to make a candy that dissolves very slowly in water. I am bringing sugar to its hard crack stage and pouring it into a mold. Once hardened, I place in water and it dissolves too rapidly (within minutes). Any ideas or suggestions of what I can add to the sugar to slow this down so it will last a really long time?

Thank you!

[Intanjir]

Rock candy would have a different dissolution rate. It might be significant longer than hard crack but internet searching didn't immediately lead me to an answer.

It might be possible to add isomalt to your hard crack, or to use it instead of the sugar. I believe that it typically dissolves more slowly than sucrose. At the very least they commonly use it in sugar free lozenges, so it can't be super fast to dissolve.

[Muddy]

That's a great idea, thanks. I will give that a try and see the difference it makes. I will post the outcome once tested.

[Furanone]

First, I just want to say I do not have direct experience with what you are attempting to achieve, but I can make a suggestion which "theoretically" could work.

Intanjir's suggestions of using a different sugar with different dissolution rates is a good suggestion and may work. If not, maybe try adding a very small amount of a food-grade gum that has gelling capabilities, such as agar or kappa carrageenan. Probably agar would be better since it is typically much higher molecular weight and creates gels at much lower concentrations than carrageenan. Typically a firm agar gel can be made with under 0.5% in water but in a concentrated sucrose matrix you could get away with much lower amounts such as 0.2-0.3%. Hopefully this little amount added should not change the texture of the candy too much, but will create a network that 'should' slow dissolution.

My thinking is that kappa carrageenan is used to make those gel air fresheners, and as they slowly dehydrate they allow the entrapped essential oil aroma volatiles to escape over a steady time-release keeping your room smelling nice for a few weeks. Also, trying to re-dissolve an agar or carrageenan gel in room temperature water is very slow indeed.

[Muddy]

Great idea, I will implement that as well and see if it gets the results. Hoping to test soon and will post. Thanks.