The importance of the fermentation process in the production of spirits is well established and recognized still. This importance given to the fermentation process is almost always limited to transforming sugars into ethyl alcohol; however, the fermentation of musts in the development of each beverage's sensory profile is hardly ever recognized.
In this blog post, I will discuss the chemical compounds generated during this crucial process and their contribution to tequila aromas. Let us recall that smell is the sensation caused by the impact of aromatic particles (volatile compounds) on the olfactory epithelium in the nose. The sense of smell is the most developed sense we have at birth but usually not the most cultivated during our development. Adults can distinguish between thousands of different aromas, even those associated with compounds found in deficient concentrations.
The chemical composition of tequila has already been explained in another post; tequila is a very complex distilled spirit in which, aside from alcohol and water, the most abundant compounds in this liquid, we also find hundreds of other compounds, the ones we call congeneric. These congeneric compounds are the ones that contribute to the identity of tequila's chemical and sensory profile. We could use the sommeliers' language to describe tequila's sensory profile. Still, suppose we want to go to the bottom of the matter. In that case, we must take a look at each of the production processes, as well as the chemical reactions generated by the compounds, since they are the ones that contribute to the development of each specific profile.
Compounds found in tequila
The inputs and process parameters are critical for the fermentation process: agave juice, other sugars (in the case of tequilas that are not 100% agave), yeast, nutrients, operation temperature, fermenting tank... all of them have to do with the presence and contribution of each of the compounds that are generated throughout the process. In this post, I will briefly talk about two of the most essential chemical groups:
A) Carbonyl Compounds
This group is essentially made of aldehydes and ketones. They are the most critical components of the aroma because even at low concentrations, usually two or three times lower than those of the alcohols, they are still sensory perceptible. Overall, its aroma is perceived as fruity or as green leaves.
The most common carbonyl compounds are:
Makes up more than 90% of the total aldehyde content. It is an intermediate product of yeast metabolism. Its production occurs during the first stages of the fermentation process and, in many cases, is parallel to ethanol formation. Acetaldehyde at low concentration levels provides a pleasant fruity aroma, but it offers a pungent irritating aroma similar to a rotten apple at high levels. It is a key contributor to Casa Sauza's tequilas.
Diacetyl (2,3-butanedione) is produced during alcoholic and malolactic fermentation. Diacetyl is accumulated during alcoholic fermentation due to the oxidative decarboxylation of alpha-acetolactate, a compound synthesized by S. Cerevisae and excreted outside the cell.
Diacetyl is reduced to acetoin, reaching its highest level in the middle of the fermentation process. After that, the levels notoriously decrease due to their reduction to 2,3-butanediol. Diacetyl and acetoin provide pleasant butter aromas when specific concentrations are not exceeded. They are not an essential element for our tequilas.
They represent the largest group of volatile components and are very interesting due to their intense and pleasant smell associated with flowers and fruits. They are mainly formed during the first fermentation stage by condensing an alcohol and an acyl group provided by an acyl coenzyme-A. They also originated in the distillation or during the aging processes in barrels through biochemistry. The most common compounds are the following:
This group is the most abundant, given the abundance of ethanol, followed by amyl and propyl esters. Ethyl acetate is the most abundant ethyl ester, and its presence is desirable at certain ranges when it has a specific pineapple smell. When its concentration exceeds the desirable ranges, its contribution to the aroma is negatively affected, offering a varnish and solvent smell.
It is produced during fermentation and is distilled as a "heads" product. Its content is higher in rectification than in destruction.
This compound is distilled as a "tails" product. It contributes to a fruity aroma.
These two main compounds are carefully controlled in our tequilas due to the meticulous distillation process that we carry out. You now know about tequila's fermentation process and aromas; I will increase our sensory inventory in my following posts. Cheers!
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