The Spirit Within: The Effect of Ethanol on Drink Perception
Alcohol is hardly known to be the most health-conducive substance on earth. Next to being associated with a whole slew of unwholesome degradation processes in the body, alcohol’s uplifting and creativity-endorsing effect the night before can be quickly counteracted by the dreaded morning afterwards. So why is it that we incorporate it into nearly every drink we have at a bar? Why don’t we switch to mocktails and mix juices and non-alcoholic infusions? As it turns out, ethanol (the chemical substance we label as ‘alcohol’) has a panoply of interesting characteristics we value. Next to its eligibility as a solvent in infusions and its ability to evoke the slightly inebriated feeling we sometimes crave for, ethanol has a distinct and measurable influence on the flavor perception of a drink which we will explore here.
To start out small, let us begin with a simple mixture of ethanol and water and point further up the complexity ladder where appropriate. While hardly comparable to the chemical (and flavor) complexity of a barrel-aged whiskey, many of the distinct characteristics of an alcoholic solution can already be found in this model solution. First of all, the most straightforward feature: taste. From about 1.4% ABV on, ethanol can be sensed by our tongues. Overall, ethanol-water mixtures are perceived as predominantly bitter and slightly sweet. Interestingly enough, so-called supertasters perceive alcohol as overwhelmingly bitter. Starting from about 20% ABV onwards, a burning sensation enters into the mix, dominating the tasting experience at higher ethanol levels. This irritation is not an actual taste, but rather the activation of vanilloid receptor-1 (TRPV1) which, not coincidentally, also binds the main contributor of the hotness of chilis, capsaicin, and signals through pain nerves. As you may remember from your younger days, ethanol is an acquired taste which is rarely consumed voluntarily above 6% ABV by uninitiated humans (or rats for that matter). In addition to that, ethanol also exercises its own brand of astringency by drawing out the water from your cells and leaving your tongue in a dry state.
A lot of research has been done on the effect of ethanol in wine, especially since trends in the industry have come to favor alcohol-heavy wines. Similar to our simple ethanol-water mixture, the immediate effect of increased alcohol content in wines is enhanced bitterness, slightly increased sweetness and a somewhat increased burning sensation. On top of that, researchers have also found ethanol to decrease sourness in these contexts. Completing the picture, research focussing on the effect on aroma has found that increased ethanol content decreased floral and fresh fruit aroma in wines but increased aromas such as wood and pepper. So if you de-alcoholize wine (by vacuum destillation), you end up with a stronger fruit aroma and a stronger sour taste. The harsh taste of high ethanol concentrations in spirits is thankfully mellowed by organic acids initially remaining from the destillation process which are amplified by barrel-aging and strengthen the interaction between water and ethanol molecules. As you maybe have gathered by now, the effect of ethanol on taste and aroma is a complex issue, masking some attributes while enhancing others. Yet until now, we have not discussed the most interesting characteristic of ethanol.
Ethanol is made up of two parts, one part which interacts with water and one so-called hydrophobic (water-avoiding) part which would rather interact with something else (or with other ethanol molecules). This hydrophobic part is the reason why some oily substances are soluble in ethanol, but not in water. Below 15% ABV, ethanol is so sparse that we can regard it as being dissolved in water. Likewise, above 57% ABV there is so much ethanol that now the water is more or less dissolved in ethanol. The most interesting part however lies between 15 and 57% ABV. In this range, there are enough ethanol molecules to find each other. By spontaneously forming micelles (hedgehog-like balls of aggregated ethanol molecules), they expose their water-loving parts to the water molecules and bury their hydrophobic parts in the interior of the aggregate where they can interact with other ethanol molecules (leading to a loss of volume if you mix water and ethanol in this range). This preferred packing of ethanol molecules becomes especially important at the surface of a drink, where you typically find a higher ethanol concentration than in the bulk drink. Here, it is easier for the ethanol molecules to shield their hydrophobic parts from the water, as the surface itself offers them a water-free backdrop.
Why is all of this important for a cocktail? Because ethanol traps aroma. Typically, aroma is generated when particular chemicals escape from your drink into the so-called headspace where they can be smelled by you. This escape is helped by the fact that most aroma molecules do not particularly like to be dissolved in water and are more than a little bit happy to escape its grasp. But if you add ethanol to your drink, these elusive aroma molecules are now considerably more comfortable in their liquid home. By concentrating ethanol at the surface of a drink, the very launch pad of aroma generation, aroma molecules are hindered from soaring off into the headspace. How effective this process is depends on the physicochemical properties of the aroma molecule (specifically how well it dissolves in ethanol). But do not fret: by remaining in your drink, these aroma molecules will contribute to the flavor of your drink and, through a process called retronasal smelling, reach your nose through the back of your mouth. And while there are many more physical processes going on in your drink which I did not go into here, isn’t it nice to know that you can calmly take a sip from your drink while the combination of the physicochemical processes create a thoroughly enjoyable experience for you?
