I purchased a Montepulciano, added 80 grams of honey and some pepper, and then put it in the fridge. A glass of it after 24 hours seemed to me more alcoholic than what it was originally. Is it psychological, as I had read this was the case (but can't find the source right now, and I tend to think it's not true), or is the increase of ABV real?
It's pretty unlikely.
Given that it was a commercial wine I don't there was much live, viable yeast in the bottle. Particularly if sulfites were added, triggering additional fermentation would probably be difficult.
On top of that, refrigerating it for the whole 24 hours means that, even if there was viable yeast uninhibited by sulfites, it's very unlikely it much fermentation could occur. It's possible you could see some fermentation due to the Crabtree effect but it wouldn't have been much.
Highly unlikely that the alcohol went up. Four reasons.
- The alcohol already in the wine is a barrier for the yeast to re-ferment.
- The sulfites in the wine could inhibit refermentation if it hasn't dissipated yet.
- The cold temperatures that will also inhibit fermentation.
- Many commercial wines are sterile filtered so yeast counts are zero to very, very tiny.
So, in 24 hours it's highly unlikely that it fermented again. Your perception of alcohol may be enhanced by the sugar that you added. High alcohol wines routinely taste "sweeter" to many people even though sugar levels are low. You might have tricked yourself into thinking sweet wine = higher alcohol.
The feeling of alcoholicity, at tasting, is very dependant of many factors, such as temperature of beverage, sugar, glycerol and a few other molecules content, and of course personal abilities of the taster as well as the preceeding tastings. Concerning the present situtation, a simple experiment is a comparative tasting : keeping two glasses of the same wine, in closed glasses (sealed with plastic film to limit oxygenation/oxidation), put them aside the honeyed bottle in the fridge ; then a few minutes before tasting, get them all off the fridge, serve a glass from the bottle ("glass 1"), in "glass 2" (one from the fridge) add the same relative quantity of the same honey that was added in the bottle, and in the last fridge glass ("glass 3"), add the same relative quantity of white sugar. Again seal the three glasses in order to mix "2" and "3", and let them dissolve their addings (without forgetting to shake "glass 1" as much as the 2 others), and finally get all three be at the same temperature. Then taste, or better, have someone taste them without knowing which is what (blind tasting)… Not a complicated experiment, but sure the best way to know. My bet is "1" and "2" will be considered almost the same, and eventually a bit more alcoholic than "3".
And my proposition for an explanation is that in honey, there are other molecular chemicals that enhance the feeling of alcohol (ethanol) (other "-ol"s and esters…?).