Forgive me if this is a really silly question - I am very very bored and lost my restraint.
I’ve never noticed that they do.
Is English JD different than the American version? Cause to me, it smells like lighter fluid. The JD, I mean, not the bananas.
I hope they find your restraint, and fit you back into it ASAP.
It only comes from the Hollow.
-postcards, a Tennesee Squire since 1991
andrewt… very droll 
It smells a bit like lighter fluid that might have come out of a banana shaped lighter…
Actually, I’ve never noticed any “eau du banane” in my Jack- perhaps you’re using dirty glasses?
If you’re bored, you can Google “esters” or “amyl butyrate” with a combination of “bourbon” type phrases and see what you get, or wait until someone smarter comes along.
IANAD (I am not a distiller.)
Isn’t there a non-ethanol type of alcohol which was once used as an artificial banana flavoring?
Esters in the alcohol.
In beers, these are typical off-flavors (unintended flavors) which give the beer it’s character. Wheat beers, especially, are quite estery.
That’s a little bit scary to me, because isoamyl acetate’s chemical parent is isoamyl alcohol, a very not-fun substance which probably shouldn’t be hiding in a bottle of liquor, even in trace amounts.
I’m sure that can’t possibly be the cause for the scent. Well, I hope I’m sure, anyway.
I wouldn’t worry about isoamyl alcohol being released from isoamyl acetate. The concentration of it in alcohol is probably low enough that before that killed you the good old ethyl alcohol would. The lethal dosage of isoamyl acetate for 50% of the population (LD 50) is about 7.5 grams per kilogram( for labrats, source) , while the LD 50 of ethyl alcohol is about 7 grams per kilogram. (for labrats,source) In other words to be a major threat the isoamyl acetate concentration would have to be nearly as high as the ethyl alcohol concentration.
Funny thing: I read the OP, thought…no way! So I headed for the kitchen, and took a nice big sniff of Jack to better describe the smell Lobsang was obviously driving at…low and behold, the bloody stuff smeels like Bananas!
I never noticed it before I took a deep, long sniff right from the bottle neck, but it surely does!
I’ve noticed that Jeff Daniels also smells of bananas.
“smeels”… ha ha ha ha …I need to stay away from that stuff!!!
Not to mention “low and behold”…
Seriously, I`ve noticed this too.
You can`t take a strong whiff with your nose in the bottle. You have to sort of take a faint sniff as you approach the open bottle and at that point you can sort of smell the bannana-ish smell.
Not sure what the connection is though.
Any dopers live in Lynchburg? (pop. 361) and who possibly knows a certain Lem Motlow?
Having already weighed in with some spelling pedantry, I may as well give a proper and factual answer too 
The fermentation process doesn’t just produce ethanol - it also yields higher alcohols (those with a larger molecule). One of these is 3-methylbutanol, which has a banana-like aroma.
So, this is one source of the scent, but probably a more major source are the esters, which are also formed during fermentation. The following cite is related to beer, but it’s reasonable to assume that similar substances are retained in whiskey, as whiskey is basically just distilled beer :).
From http://www.vlb-berlin.org/english/books/kunze/c4_1.html
The same page mentions the following compounds as having banana-like aromas: the aforementioned 3-methylbutanol and the esters isobutyl acetate and isoamyl acetate.
By the way, you shouldn’t worry about these esters being “toxic”, as they are present in very small amounts. The fruit flavouring in candy (and in fruit itself, for that matter!) is basically just esters, too. The higher alcohols are fairly nasty things, and contribute to hangovers.
A Googled point to ponder:
From http://www.adamsbevgroup.com/cheers/1999/0199/199crnt.asp
it appears that the excess banana is considered a bad thing:
From http://claymore.wisemagic.com/scotradiance/bell/bell9711.htm
As the whiskey ages, the whiskey barrels “breathe.” Because of this phenomenon, somewhere between eight to ten percent of the alcohol volume will be lost to evaporation in the first year. Evaporation continues over subsequent years at a rate of four to five percent per barrel. A good whiskey is likely to lose approximately thirty percent of its original volume by the time it is ready for bottling.
From Jack`s web site .
Also this;
Fact #1: Mellow Out
Charcoal-mellowing refers to a process used to make Tennessee whiskey, such as Jack Daniel’s. The process involves slowly dripping the newly made whiskey through giant containers hard-packed with 10 feet of sugar maple charcoal. The process takes ten days, and during this time the whiskey absorbs the essence of the charcoal, refining the spirit and giving it a unique flavor and aroma.
Fact #5: Number One With a Barrel
Whiskey barrels are assembled from American White Oak, and that’s because American White Oak just happens to have the right combination of compounds to create the tastiest whiskey. These compounds, referred to as such because they have really confusing names, are exposed when the insides of the barrels are charred by open flame.
Since the heavier alcohols don`t evaporate as easily as the lighter ones, you leave behind more of the “banana” scented alcohols.