Unlike other tequila production steps, fermentation is one of the few steps out of the control of human beings. Fermentation is the conversion of sugars and carbohydrates to alcohol through yeast in aerobic conditions, meaning that oxygen is present during the process.[1] Fermentation is also carried out in a non-aseptic environment which increases the bacterial activity of tequila.[2] The participation of microorganisms from the environment (yeasts and bacteria) makes fermentation a spontaneous process which gives rise to many byproducts that contribute to the flavour and aroma of tequila.[2]
During the fermentation process, inoculum is added to the batch to speed the rate of fermentation. When inoculum is added, fermentation can take approximately 20 hours to 3 days. If inoculum is not added, fermentation could take up to 7 days. The rate of fermentation is a key factor in the quality and flavour of tequila produced. Worts fermented slowly are best because the amount of organoleptic compounds produced are greater. The alcohol content at the end of fermentation lies between 4-9%.[2]
These compounds enhance flavour and aroma. In this section fusel oils will be focused on.
Tequila Fermentation Vessel in City of Tequila MuseumFusel Oil (alcohol): Production of isoamyl and isobutyl alcohols begins after the sugar level is lowered substantially and continues for several hours after the alcoholic fermentation ends. In contrast, ethanol production begins in the first hours of the fermentation and ends with logarithmic yeast growth. The alcohol content in tequila is affected by three factors. First the amount of isoamyl alcohol and isobutanol is the yeast strain. Second, the carbon:nitrogen ratio. The higher the ratio, the more alcohol produced. And third, the temperature of fermentation. The higher the temperature, the greater concentration of isobutyl and isoamyl alcohols produced. Although if temperatures are too high, this can cause the yeast to become less effective. Similarily, if the temperature is too low, the process occurs too slowly.[2] This can become a large issue in Central Mexico, most precisely the city of Tequila, Jalisco, where most tequila is processed. The average annual temperatures in the city of Tequila can reach 31C.[3] For this reason, tequila producers often use large stainless steel tanks for fermentation.[1] The high molecular weight of alcohol compounds (fusel oil) is what contributes to hangovers.
Organoleptic compounds are dependent on yeast. The role of yeast is to, through many enzymatic processes, turn sugars and carbohydrates into alcohol. There are two steps, first in aerobic conditions, yeast is doubled in colony size every four hours. This process goes on for 24-48 hours. Next, yeast turns acetaldehyde (also known as glycerol) into ethyl alcohol which is known as one of the organoleptic compounds produced in fermentation.[1]
The two main categories of yeast used in tequila are Commercial brewers yeast and yeast that comes from pre cultivated existing yeast that has been preserved. The use of either type of yeast can result in different end products of tequila.[1]
Tequila is a distilled beverage that is made from the fermentation of the sugars found from the blue agave plant once it has been cooked, the main sugar being fructose. [4]Through the fermentation process, many factors influence the higher alcohol content of tequila, which are molecules such as isobutyl alcohol and isoamyl alcohol, and ethanol.[4] These parameters include, the type of yeast strain, the age of the agave plant itself, temperature, and the carbon/nitrogen ratio. However, the type of yeast strain used and the carbon/nitrogen factors have the biggest influence on the production of higher alcohols, this is not surprising as higher alcohol and ethanol production is an intrinsic property of the metabolism of each strain[4]. The type of yeast most commonly found in tequila is Saccharomyces cerevisiae, which contains many strains.[5] For example, CF1 agaves, a type of yeast, produces much more ethanol than a strain of CF2, as the yeast’s metabolism mechanisms differ from one another.[4] This factor may be influenced from different agricultural practices that occur to cultivate the different yeasts strains. It was found that the higher the carbon/ nitrogen ratio, the higher the production of higher alcohols such as isobutyl alcohol and isoamyl alcohol. A high ratio imparts that there is less nitrogen in the fermentation process, which results in deamination reactions of amino acids, leading to the synthesis of higher alcohols.[4] The Ehrlich pathway is the name for this process, where a-ceto acids are decarboxylated and transformed to aldehydes and to higher alcohols.[5] The temperature of the fermentation process also greatly effects the alcohol content of the resulting product. For example, in a study conducted by Pinal et al., they found that cultivating two strains at a temperature of 35 degrees as compared to a temperature of 30 degrees produced more isoamyl alcohol. The higher temperature suggests that this is a much more optimal condition for the yeast to ferment the distilled beverage.[4] Lastly the age of the agave plan itself, the older the plant the greater the alcohol production. It was show in a study that the concentration of amyl alcohol increased as the plant aged by a factor 30%. However, it is also found that there is a higher concentration of methanol found when using younger plants. This may be due to differences in agricultural practices that occur when taking care of plants of different ages. [5]
Tequila comes in an abundant array of colours that ranges from a simple clear distilled beverage to a dark amber brown. The colour of the tequila varies greatly on the aging process and the type of wood used for storage.[6] The white version of tequila, known as silver tequila or blanco, is the product obtained without or very little additional aging process. As well, the spirit must contain between 38-55% alcohol content, which is fermented from a wort, which contains no less than 51% sugars from the agave plant. [6]Consuming silver tequila provides for the purest form as little aging has occurred. What is know as gold tequila (joven or oro) is simply white tequila with the addition of a caramel colour added to it.[6] Rested (reposado) or aged tequila (añejo) are simply the white distilled liquid that is then aged further in wood containers.[6] The aging process can last anytime between 2-12 months and this can enhance and create flavours and aromas that may be distinct to certain types of tequila. Due to this again process, the liquid takes on a gold hue, that is present due to the container in which it was aged. [6]
There are more than 300 known compounds in tequila, many of which are produced during the fermentation process, the raw material used, and to a lesser degree, during the maturation. [7]The components that make up tequila do not act individually to give tequila its distinctive flavour and aroma, but rather, depends on the interaction and quantity of each volatile compound.[8] The volatile compounds responsible for the flavour and aroma profiles of the tequila are put into a category called organoleptic compounds and are known to increase in concentration with a slower fermentation process.[9] The organoleptic compounds produced during fermentation include higher order alcohols, methanol, esters, carbonyls, terpenes, and furans.[8]
Higher order alcohols have a strong aroma, and the quantity present in each tequila depends on the Carbon: Nitrogen ratio and temperature during the cooking and fermentation processes.[9] Some of the most common alcohols present other than ethanol are: isoamyl alcohol, isobutanol, and 1-propanol.[8]
Methanol is thought to be mainly generated through hydrolysis of methylated pectin which is naturally present in the agave plant, but there has been speculations that it is also partly produced from the enzymatic reactions of yeast strains containing pectin methyl esterase enzyme which break up the methoxyl group from the pectin.[8]
There has been nearly 50 different esters identified in tequila, which together give rise to the fruit like flavours and smell.[8] One of the most abundant esters is ethyl acetate and is synthesized during fermentation by the yeast strain Saccharomyces cerevisiae, by using alcohol transferase enzyme which links acetic acid to ethanol.[8] In general, the longer the carefully controlled fermentation period, the higher yield of esters produced.[9]
During the fermentation process, ethanol is oxidized and one of the main compounds produced are acetaldehydes, which adds the flavour necessary for the final product of tequila.[8]
The agave plant contains many terpenes such as vanillin and syringaldehydes which presents a strong and fruity or herbal aroma. The agave plant also contains eugenol which can deliver a hint of spicy flavour to the tequila.[7]
Since the production of tequila involves heating, Maillard browning reactions occur, and furans are produced during the thermal degradation of sugar. [10]The most prominent furanic compounds include 2-furaldehyde and 5-methylfuraldehyde[10], which can contribute to the smoky flavour of tequila[9].
Quantitative and Qualitative Analysis of Flavor and Aroma
Volatile compounds that contribute to the overall taste and aroma of tequila can be quantitatively assessed and evaluated by Gas Chromatography[8]. Moreover, discrimination tests such as duo-trio and triangle tests are used to evaluate the quality of the tequila.[7]
If silver or white tequila is the desired final product, distillation is the final process it undergoes. Rested (Reposado) or aged (Añejo) tequila must be maturated in 200-liter (or larger) white oak barrels for at least 2 months for the first, and 12 months for the last. There are, however, more than 50 different companies producing tequila in the mexican province of Jalisco, with different maturation times according to the variety of tequila and desired quality of the final product.
All companies producing tequila have their aging processes regulated and fiscalized by the Mexican government.
The maturation process causes four main chemical transformations to the tequila compounds: (1) decreasing of fuel oils by the char in barrels, which acts as an adsorbing agent. (2) extraction of complex wood constituents by tequila, yielding specific aroma and flavour to the final product. (3) reactions among the components of tequila, creating new chemical compounds and (4) oxidation of the original contents of tequila and of those extracted from wood. The final result of these changes are increased concentrations of acids, esters and aldehydes and a decrease in fuel oil concentration.[2]
Unlike wine that contains tannins which may change over time, even in a bottle if proper storage conditions are not met, spirituous liquors like tequila do not change much once they are bottled.[11] Since tequila is a distilled liquor, it does not require strict storage conditions like wine does, and the same goes with most other distilled spirits such as whiskey, rum, or vodka.[11] Furthermore, because the characteristics and certain quality (flavour, aroma, colour, etc.) of the tequila are determined during the aging process inside wood barrels, the quality of the tequila should remain relatively constant after they are bottled.[11] To maintain the quality of tequila, at least three conditions should be met: constant and moderate temperature (60 to 65°F), no exposure to direct sunlight, and maintenance of proper seal of the bottle. Also, storage conditions will have more effect on the taste of aged tequila rather than the un-aged tequila.[11] For instance, if stored in improper conditions, the dark and more complex flavours of the añejo tequila are more likely to be tainted than the blanco or the silver tequila.[11]
Once the bottle is opened, the tequila will be subject to oxidation which will continue to happen even if no more oxygen is introduced. In addition, if the bottle has more room for air, the process of oxidation occurs faster on the liquor remaining inside the bottle.[12] Therefore, it may be the best to consume the tequila within one or two years after opening.[11] For the most part, the change in quality of tequila is due to extreme conditions of improper storage, not due to oxidation.[12]
According to the Food and Drug Regulations[13] in Canada:
·Tequila is included in the term alcoholic beverage. It is under the category of Liqueurs and Spirituous Cordials[14].
·Listed in B.02.090, only Tequila produced and consumed legally in accordance with the laws of Mexico can be labelled, packaged, sold or advertised as Tequila. A person may adjust Tequila's strength with water.
(1) Subject to subsection (2)[15], no person shall label, package, sell or advertise any food as Tequila, or in such a manner that it is likely to be mistaken for Tequila unless it is Tequila manufactured in Mexico as Tequila in accordance with the laws of Mexico applicable in respect of Tequila for consumption in Mexico.
(2) A person may modify Tequila that is imported for the purpose of bottling and sale in Canada as Tequila by the addition of distilled or otherwise purified water to adjust the Tequila to a required strength.
