Hi Big Poppa, I’m somewhat surprised that no one has answered your question!
First up I’m no chemical Tech person or Master distiller but I do know under certain conditions you can end up with condensation in the neck of the bottle after….
1. Bottling shortly after diluting NGS (neutral grain spirit). Due to exothermic reaction heat is created causing some evaporation . Which leads me to say you should let the diluted spirit sit and marry together for some time before bottling.
Olny guessing here.
2. Bottling your spirit below 40 ABV. H2O will condence out of most GSN spirits below 40 % ABV. A common mistake is measure the new make spirit while it’s warm and not factor the tempeture calibration aspect into whole deal.
3. Long shot, maybe your getting some higher alcohols condensing out, (more volatile alcohols, “Heads”), epaverating in the bottle during high room heat. Meaning, poor head cuts?
I really don’t have any hard answers, like I said, I’m just me, I follow this site to learn about the do’s and don’t. And I’ve I got to go, my son is driving cross! Sorry
Cheers
Marc