In my first year if university the coolest thing to do was take a shot of "Alcool", you can't even buy it here in Ontario. At 94%alc/vol it was dangerous stuff, put a drop on your arm and it would get cold as it evaporated so quickly. But what I remember most distinctively is knocking back a shot and thinking, "Where the f*** is the fire department?". My mouth was on fire, my eyes teared up, gasping for air, I began salivating and I could feel my stomach eroding from within.
But why does alcohol feel "hot", in any given boozy beverage the main type of alcohol is Ethyl Alcohol. This is the alcohol that greases the gears, keeps you up all night and has made a lot of babies. But there are also not so nice alcohols such as Methyl, Butyl and Propyl alcohols. Now these are in very, very, very small quantities, but are primarily responsible from your head shaking and squirmy face after a shot.
These alcohols trigger a type of receptor on your taste buds called "VR1", ethyl alcohol triggers "VR1"as well but not to the same degree as these higher alcohols. This is the receptor that also senses hot peppers and spicy foods.
The receptors have a threshold of 42 Degrees Celsius, meaning that if you were drinking coffee at 43C, you tongue would feel hot. Capsaicin, the ingredient that makes most spicy food spicy, when it gets in contact with VR1, it triggers the receptors to think your tongue is above 42C. This triggers the sensation of heat even though the actual temperature of your food is below the temperature threshold.
But here is where it gets really cool! When alcohol gets in contact with these receptors, it makes the receptors more sensitive. So rather then the temperature threshold of 43C, it is lowered to 37C. So where does the "heat" come from? You! Your body temperature is about 37C, it is your own body heat that is making your tongue hot.
Of course you have taste buds on your tongue, but you also have them on the roof of your mouth and your throat. That is why you can feel the warmth all the way down the hatch.
More alcohol = more burn. That is why drinking a beer has never set your mouth on fire. But why are some spirits "smoother", meaning less hot? Well it comes down to how the vodka, gin, whisky etc. was distilled. Vodka has less of these higher alcohols due to its distillation process and by some is generally considered to be a "smoother product. When whisky ages in the barrel, some of these alcohols evaporate, get absorbed by the barrel or convert to compounds that actually taste good. So in theory, but not always true, older whisky is "smoother".
Its not the alcohol that is hot. It's you!