The "condensation" contains juice residue and will crack certain plastics the same way juice will. But unless you're made of plastic, it's probably safe for you.
Polycarbonite, which is what most "clear' tanks are made of, is fairly susceptible to damage from esters and very susceptible to damage by Aldehydes
Cinnamaldehyde, which is what gives Cinnamon it's flavor is an Aldehyde. You don't want to use anything with that in it in a Polycarbonite tank. It's safe for you, but it will very quickly and spectacularly destroy Polycarbonite.
Esters are created when you mix a carboylic acid with an alcohol. PG is an alcohol. Acetic Acid (gives Vinegar it's sour taste), Citric Acid, malic acid & tartaric acid are all carbolyic acids used fairly regularly in juices & flavorings which when mixed with PG and heated can create esters which then attack the plastic causing it to fog, soften, "melt" or completely disintegrate (depending on the concentration of esters present and how long they are allowed to attack the plastic).
Esters are prevalent in nature and many natural foods and most are non-toxic to humans. But to some plastics, they're death.
A simple way to check your juices for this kind of reactivity is to take some juice and put it in a small container. Break off a small piece of Styrofoam (polystyrene) and add it to the juice. Set the juice in a warm location (I put it on top of my DVR which is always fairly hot) and leave it for a week. If the styrofoam is unaffected, the juice is probably ok to use in a tank. Styrofoam reacts to most of the same things Polycarbonite does, often much more quickly. If the styrofoam dissolves, you probably don't want to use that juice in a clear plastic tank.
It's not a 100% accurate test as some things that will dissolve styrofoam are fine in tanks and vice versa but, for our purposes it's close enough and better than blindly risking a tank.
