Where Does Rum Flavor Come From
Rum’s wide diversity in aromas and flavors results from skilled rum makers using many variations of the core rum-making processes to craft their signature profile. While tasting notes often use everyday experiences to convey a rum taste, there are other ways to understand a rum’s character.
All distilled spirits are mostly just water and ethanol, the latter being the type of alcohol we can consume in moderate quantities. However, ethanol and water contribute very little to a spirit’s taste. Instead, the flavor comes from very small quantities of other molecules.
We experience these molecules throughout our daily life, not just in distilled spirits. More formally, they’re known as organic compounds. Each variety of molecule triggers our olfactory system to send a particular signal to our brain, which interprets the signal as an aroma or flavor. One molecule may evoke the smell of fresh grass, while a second brings to mind pineapple, and a third, green apple. Distilled spirits are a soup of hundreds of different types of flavor molecules; the particular ratio of molecules present shape the aromas and flavor we detect.
Each phase of rum making influences the mix of organic compounds present. Fermentation creates many types of organic compounds, and the source materials and yeast strain strongly influence the resulting flavors. Distillation concentrates certain types of organic compounds and filters out others. Aging and blending further shape the compounds found in the final spirit.
Going a little deeper, a rum’s organic compounds fall into several chemistry categories, including acids, alcohols, and esters. For our purposes here, we don’t have to go very deep into organic chemistry to understand them. Let’s look at some simple examples.
Acid Molecules: The most familiar type of acid molecule is acetic acid. We experience it in everyday life as vinegar, i.e., acetic acid diluted with water. Other acid types are butyric acid, which smells of spoiling milk, and Lauric acid, which evokes “fatty” aromas of coconut and soap.
Alcohol Molecules: The ethanol molecule is by far the most common alcohol found in rum. All other alcohols exist in far lesser quantities. For example, isopropyl alcohol, which we know as rubbing alcohol, and 2-butanaol, which smells of peaches.
Ester Molecules: Esters are molecules formed from an acid and alcohol molecule binding together. Different combinations of alcohol and acid molecules create different esters, each with its own sensory experience. Rum’s most common ester is ethyl acetate, formed from acetic acid and ethanol. This ester smells fruity in low concentrations but like nail polish remover at higher concentrations. Isoamyl acetate, comprised of acetic acid and isoamyl alcohol molecules, smells of banana. Just ten types of alcohol molecules and ten types of acid molecules are responsible for 100 different esters, and many more varieties of esters exist.
While all rums have esters, Jamaican rum is historically associated with esters. In fact, certain Jamaican rums have an order of magnitude more esters than other rums. We will take a closer look at Jamaican rum, esters, and styles like “Plummer” and “Wedderburn” in a subsequent post.
Scientific tools like the gas chromatograph allow us to measure the type of molecules present in a spirit and how much of each. The amount of a particular organic compound in a spirit is typically expressed in grams per hectoliter, commonly abbreviated as gr/hl or gr/hlAA. For instance, a label saying that the esters are 100 gr/hlAA means that 100 grams of esters molecules are present in every 100 liters (hectoliters) of rum.
While these scientific tools are extremely helpful to researchers in learning non-judgmental information about a distilled spirit, their sensitivity is no match for the human nose. For this reason, no rum makers depend entirely on gas chromatography for blending decisions. That role is reserved for the well-trained nose of the master blender.
Rum glass