We read in the papers that Swedish scientists claim to have found proof that adding water to whisky will make it tastier. To be fair to Professor Bjorn Karlsson, who led the research, he does say that the balance will depend on the concentration and taste compounds that are characteristic of each whisky. However, it is also claimed that, similar considerations can be used to optimise the alcohol concentrations of other spirits including gin, rum and brandy. Drinking cognac with water is certainly a topic for discussion.
We are not scientists but we do taste thousands of cognacs and we do sometimes add water to cognac. Adding water is about creating the optimum balance i.e. maximum flavour and minimum bite. That said, when we do add water to reduce a cognac it is done very slowly. With cognac strengths close to 40% alcohol by volume, it can take years for the added water to create an acceptable balance. Indeed, water can be detected on the palate in the early stages of dilution as water and spirit are notoriously difficult to blend together.
Whisky is of course different from cognac both in taste and chemically. Cognac can provide thousands of different flavours as it is the result of a wine distillation rather than distillation from grain. However, taste is not the complete sensation as aroma also provides a fuller mind perception which enhances our enjoyment of cognac. It is believed that 50% of the perception of taste comes from the aroma. Sometimes aroma can be blinded by the alcohol content but the addition of water can also dilute the aroma and hence the total enjoyment. Conversely, some cognacs are enhanced by a greater alcohol content. Good examples are our Hermitage 1975 and Hermitage 1987, each with a strength of 47% abv.
Everybody's perception of taste can change but adding water in the glass to high quality cognacs (and I suspect whisky) to improve the flavour is a myth. Apart from the slightly oily effect created on the palate when the water is added, it also changes the alcoholic strength. This will dilute the aroma in the glass which, of course, in turn reduces the flavour. Pure alcohol has no smell but it enhances the flavour of the cognac. However, if the alcohol is released by swirling the cognac (or whisky), it will sit on the surface of the liquid and blind the aroma.
Adding water in the glass unbalances your spirit as both taste and aroma are changed. Sorry Professor, may I recommend that you start drinking your spirits, rather than testing them, to find some real pleasure in the flavour?