I should say first of all that I'd rather have an espresso than an americano any day, and I've often made the diluted booze comparison, too. I do sometimes add some water to my single malt, but only after I've familiarized myself extensively with the malt poured neat. However, a properly prepared americano can open up latent, difficult to detect flavours for palates as unpracticed as mine.
I first got interested in americanos before I knew anything about coffee because I noticed that the "good" barista at my local shop (where the coffee was bad) made an americano I could drink without cream and/or sugar by pulling the shot into the water. I experimented with this a bit on a friend's home machine and the results were consistent. This marked the beginning of my life as a drinker of black coffee, so obviously I feel a bit of attachment to the notion of the americano.
Fast forward to the 2007 SCAA expo. A friend and I got one of the Intelli baristas to run a blind tasting on the trade show floor, comparing americanos prepared using the espresso-into-water and water-into-espresso methods. Again, the results were consistent. Espresso-into-water won. I've never worked behind the bar, so I have a bad memory for these things, but I think the ratio that really worked was 1:1, espresso:water, pulling doubles.
Chemically speaking, some of you may be familiar with the concept, "Add acid to water, don't add water to acid." Strictly speaking, an espresso shot is not a sufficiently concentrated chemical solution to be compared directly to the sort of acid solutions we usually use in the lab. Even so, I remain convinced that the basis for the better flavour of the espresso-into-water version can be found in acid-base chemistry, which involves the release of a lot of heat energy when the components of an acid or base chemically dissociate (i.e., separate from each other). This heat energy is called the "heat of dissociation." Heats of dissociation are generated when more concentrated media, like concentrated salt solutions, suddenly become diluted. If the diluting medium--water in this case--is very hot to begin with, then the heat of dissociation will actually mean that the new solution should transiently become even hotter. In the case of an americano this further increase in heat should, in principle, mean that the beverage chemistry changes, resulting in flavour and aroma deterioration.
In other words, based on pure speculation regarding acid-base chemistry, and no substantiating data whatsoever, using slightly cooler water to make an americano should, in fact, improve the flavour. This has also been my experience. To summarize, I think that an americano made using an optimal espresso-to-water ratio, and using water that has been allowed to cool by approximately 10 degrees, will produce a good "entry-level" espresso beverage that will help novices get into it. Again, that was certainly my experience.
For those who think I oversimplified the above a little too much, my apologies.
R. Luke Harris
Assistant Professor, School of Health Sciences
University of Northern British Columbia