Question for JMF or someone knowledgeable about distilling and blending of spirits
I have two sealed bottles of the same inexpensive brand of Tequila - Don Sergio repo and anejo - sitting side by side.
Oddly enough, small drops of condensation keep forming on the anejo but not on the repo (or the half empty blanco sitting beside it.) I tilt the bottle to get rid of them, and the next night they are back.
I was wondering if this was a sign of something that was added to the anejo prior to bottling, such as coloring or sweetener?
Do these bottles get hit by light? Anejo is the darkest of the tequilas you mentioned. Under light (and it doesn't have to be sunlight) the darkest liquid will get warmest and is more likely to start evaporating. As an experiment you might want to store your bottles in a dark cupboard and see if the difference between them continues.
Ill try that but I doubt very much thats the case as I have other bottles of dark liquor nearby such as Bourbon and Rum and none have demonstrated this condensation. They have been in my kitchen exposed only to a low level under-cabinet fluorescent light at night, not likely to give off much heat.
Yep, that's most likely it. Oils, glycerin/glycerol (which is formed during the fermentation/distillation, although sometimes added for mouth feel), etc. from the distilling and aging process. Think of it as aromatics and flavors, that are evaporating and condensing on the neck of the bottle. It usually means that the distilling process is more of a simple artisanal pot still, rather than highly rectified spirit. (Or it's the presence of cheap additives to smooth out the spirit.)