How can I avoid crystallisation of sugars in vinegar at low temperatures? I produce high density balsamic vinegar, when it's winter and the temperatures are very low, high density products tends to crystallize. think this is a problem of over saturation of the glucose. The main sugars are glucose and fructose the ratio is 1:0.95.

I try to make products that are lower than 70 brix, or 1,35 density and 6% acidity, composed by $\ce{CH3COOH}$ and tartaric acid.

How can I exactly calculate the solubility threshold of this mixture? How can I measure it? 

How can I prevent the crystallization to happen?

Thank you very much
I can't sleep at night because of this problem !!!
It is difficult to correctly measure the solubility, especially if it goes to multicomponent solutions, as your vinegar. It is possible to find tables with some components of your mixture, but you won't get the full picture, and it looks as the moment, when the hands-on experience is most important.

Nonetheless, I found some facts for you, namely:
the solubility of a-D-glucose in all the solvents increases with
increasing temperature and decreases with increasing volume fraction
of acetic acid, from Solubilities of {α-d-glucose in water + (acetic acid or propionic acid)} mixtures at atmospheric pressure and different temperatures

Another point is that the supersaturated solution can be stabilized by various means, and I think it already happens, as your vinegar contains lot of "impurities" from the grapes.

As for the second point, how to prevent it, the simplest solution will be to keep the temperature high enough, so that the crystallization does not occur. If this is not possible, the supersaturated solution will crystallize, sooner or later. If you than ask, how to slow down the process, until spring comes, filtration could help to remove the crystallization nuclei.