The Chemistry of Whisky and Rum

For those of us who are twenty-one years and older, you may sometimes think, what is it that makes liquors different from each other? Or more specifically, what chemical components cause liquors to taste differently? This is something that you may ponder if you are out for the night with your girlfriends, or at a family dinner party. Well good for you because I have done some research, specifically on whisky and rum– just for you!

Let’s start by taking a look at the similarities and differences in taste and smell between whisky and rum. Whisky will usually have notes of bitterness, smokiness, a coconut or spice flavor, vanilla or almond/grainy, fruity flavors through the fermentation and aging process. Rum is produced differently based on the country it is made in so its taste can vary quite a bit. Most common notes are fruity, caramel, butterscotch, vanilla, and oak. You may notice that some of these tastes are similar between the two alcohols, and why does that happen? What components allow for these differences as well? This all has to with how the alcohol is fermented and aged. I will first go over how each alcohol is fermented and then what chemical components at added at certain times and how this results in a certain taste.

First let’s look at whisky. Barley is first soaked in water and then dried (the way its dried can vary by the type of whisky), then milled (mashing breaks down the starches and creates a sugary liquid called wort) and added to water. Next yeast is added to start fermentation and change the sugars into alcohol—the yeast used can also have an effect on the flavor. This fermented product is then distilled to remove the “heart” which has an alcohol content of up to 70%. The “heart” is then stored in oak barrels to age for at least three years. Pretty cool stuff!

So what about rum? It depends on the type of rum being made, but the basics are as follows. Molasses (derived from sugar cane) is mixed with water and yeast to ferment. Then the rum is distilled to make it more concentrated and then aged. Usually, rum is aged in charred oak barrels that had previously been used for bourbon production. Rum is aged for a shorter amount of time than whisky because it is usually made in a warmer climate (so evaporation happens more quickly). After being aged it can be mixed with distillates to create a uniform flavor or be filtered to make white rum.

So how do these processes result in the flavor of the two alcohols? Whisky has phenolic compounds in it that make it bitter and smoky. Some whisky comes from barley that was dried by a peat fire or is aged in charred oak barrels. The burning creates phenolic compounds that are then absorbed either by the barley or the aging alcohol. Whisky lactones are isomers (cis- and trans-3-methyl-4-octanolide) that come from the oak barrels used for aging and both can give the whisky a coconut flavor, and the cis- isomer can give the whisky a spicier flavor. Aldehydes come into play in their highest concentration from the fermentation process and some in the aging process and gives the alcohol a vanilla or almond/grainy flavor depending on which aldehyde is present. While a large portion of aldehydes are filtered out when distilled, they are still a flavor worth noting. Esters are produced in the fermentation process when alcohols are combined with fatty acids. Esters are formed with fruity flavors from this. Similar to aldehydes, most esters are removed during the distilling process, but there are still some present in the heart. Ethyl hexanote is the most prominent ester in the heart and gives off an apple aroma. In addition, because of how long whisky is aged in oak barrels it is common for oak lactones to form. Each smell or flavor is associated with a specific part of production!

Rum has some of the same chemical components as whisky which is why they have some overlap in taste/smell. Esters are present in rum as they are in whisky and can give a fruity aroma/taste. However, rum also has ethyl propanoate which gives a caramel smell and ethyl isobutyrate which gives a butterscotch smell. Rum also has phenolic compounds that are incorporated during the aging process in charred oak barrels that can lead to smoky notes and the aroma of vanilla. Oak lactones can be found from the aging process, but in a much lesser concentration than found in whisky because it is not aged as long. The important thing to note about rum is how many different ways it can be made, and because of this the flavor and smell really can vary. For example, dark rums typically have more flavor and aroma and a filtered white rum can sometimes result in the removal of compounds that are a big part of the rums flavor.

Both rum and whisky are complex alcohols to make and the entire process plays a big part in the flavors that the end product has. When these two alcohols had similar steps in production it often led to them having similar flavors (i.e.: being aged in oak barrels, fermentation).  After doing all this research it really made me question, how can two different alcohols be made in such similar ways, but not actually be the same thing?? And then I realized, just because two things have some smells and tastes in common does not mean that they are the same! For example, a honey crisp apple is not the same as a granny smith apple. They have similar components but what really makes them different are the small additions and chemical components that give them distinct flavors. Alcohols are somewhat the same. While both rum and whisky have similarities in aroma and taste—they are not the same! These aromas and tastes vary in concentration and can be altered by aging and any additions in the production process; not to mention the starting product (sugar cane versus barley).

I hope that this sheds some light on why alcohols taste the way they do and how much of an impact the brewing process has on it! I certainly had no idea how complex alcohol could be, and what a big role chemical compounds had in the flavor and smell!



The Chemistry of Rum

The Chemistry of Whisky





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