If you spend time exploring the varieties within a class of spirit, you really begin to get the differences and many come from the wash. For instance, with just a tiny bit of practice (and we know how hard THAT is), you can easily discern differences in the mash bill of a Bourbon for instance. High corn carries over as sweet, wheated has a distinctive grainy flavor, etc. Maybe these are nuances but it's something I've been focusing on recently.
This is very interesting. I came to the partial - and open to revision - conclusion that what gives the "flair" of corn, what, oats and, on a different table, the "sugary" taste of sugar wash, is the water component of the ferment which survives the distillation.
Human taste buds are miraculously selective and even 1% or 2% of the final spirit which is the original ferment water (in the case of a neutral, that is. In the case of a whisky or a fruit distillate it is more) is easily perceived with its own taste. Very aromatic substances can be traces as a distinct sample in a three-sample blind test for quantities as low as 1 part per billion actually.
Some numbers:
We ferment a wash which has 9% alcohol. 91% is "original wash water".
We distill it once: we have a wash which is 38% alcohol, and yet, 62% of that wash is "original wash water".
Let's say we dilute that to 20% with tap water and redistill: More or less, after dilution we have 30% of "original wash water" and around 30% of the brew is tap water but 30% of the brew is the "original wash water". Half of the "water" actually comes not from the tap, but from the fermenter.
When we collect let's say some 60% ABV second-round distilled product, 40% of that is water, and of this water, half of it, or 20%, still is "original wash water".
We dilute that again to ABV 20%, increasing its volume to three times the original. After dilution, we go from 40% water to 80% water. Of this water, the "original wash water" goes from around 50% to 13%.
We distill that again to a final product which is 60% ABV that goes to the barrel.
40% of this final product going to the barrel is water. Of this water, 13% still is "original wash water", therefore we still have 5,2% of the final product in the barrel which is original water.
When this 60% product is diluted with distilled water to 40% for final consumption, the "original wash water" goes somewhat below 5,2% but to around 3%.
What I mean is that if you could extract all alcohols from any wash miraculously, and add distilled water, and the last 3% of "original wash water", that 3% is enough to tell you that the distillate came from apricots, pears, apples, oats, barley, corn etc. It's not the taste of the alcohols, but the taste of the water which remains in the product coming straight from the original ferment.
3% water which is "tea" of an ingredient is IMHO clearly perceivable in a distillate.
It is probably for this reason that fruit distillates are often distilled only once (no stripping run and then spirit run). The reason why our forefathers preferred to collect the final product immediately (maybe making tighter cuts, or "aging" the product for more than 6 months to get rid of the nasty heads) is that they wanted to preserve the perfume of grapes, apple, aprcots, pears, plums in the original fermentation. They wanted to avoid the dilutions with spring water.