Fermentation

*Photo Property of Francisco Terrazas

This is the first in a series of in-depth posts that hope to shed light on the process and culture of mezcal. While we have spent a great deal of time researching these processes, we also understand that there are many different styles and traditions in mezcal culture. It is one of the reasons we love it so dearly. These pieces are in no way intended to be dogmatic, but rather conversation starters. Please feel free to ask questions if you are just starting down the rabbit hole, correct us or comment if you have experiences that have shown you otherwise. These are hopefully ways for people that cannot spend their days traipsing through the Sierra visiting maestros to share ideas and learn different customs from throughout the mezcal heartland. 

When people speak of mezcal, most of the attention and rustic romance seems to be reserved for the fiery, smoke-filled ancestral roasting process or the backbreaking, blister-causing hand crushing method. But the most complex and fascinating step may be one with the least human influence: Fermentation. How nature produces alcohol.

Fermentation has an extensive and fascinating history all its own. There is evidence to suggest that humans have been getting their drink on and intentionally fermenting beverages as early as 10,000 BC. The earliest confirmed scientific evidence of purposeful alcoholic fermentation comes from Neolithic China in the Henan province, where jugs dating back to 7,000 - 6,500 BC have been found containing residue from the fermentation of grapes, honey, hawthorne, and rice. It is around this time that alcoholic beverages began to bubble up across the globe: Beer in ancient Babylon & Egypt, rice wine in east Asia, wine around the Mediterranean, starchy fermentations in Africa, and a litany of fermented beverages in pre-Columbian America.  

When Europeans did finally storm their way across Mexico from the Gulf in the 16th Century, they discovered that indigenous people had been reaping the alcoholic potential of a host of native sources. From Balché in the Yucatan and Pulque in the central regions, to Tesgüino in the north, indigenous Mexico has one of the richest, most diverse histories of fermentation in the world. Even before Europeans brought distillation technology to Mexico, the sap of agave plants was already being used to produce a fermented beverage called pulque. While the production of pulque dates back nearly 2,000 years, agave had been a vital part of Mesoamerican culture for millennia, having been used for paper, food, textile, needle & thread, and other uses. Remnants of pit-roasted agave found in caves around Tehuacán, Puebla have been dated to 7,000 BC. The earliest evidence of Mesoamericans drinking fermented agave dates to around 200 AD and is found on a mural discovered in the Great Pyramid of Cholula, also in Puebla. It is a mural that has been named Los Bebedores and was discovered in 1969. 

Los Bebedores

It is over 180 ft. long and nearly 8 ft. tall, depicting over 150 various figures in a celebratory scene of revelry, all seen drinking a liquid out of large bowl-shaped vessels. Archaeologists believe this liquid to be pulque, the fermented sap of certain agave plants. It is believed that pulque played a large role in Aztec religious ceremonies, with consumption being restricted to the aristocracy, the elderly, and captives that were soon to be sacrificed. They were so serious about it, it even had its own deity. Patecatl is an Aztec god and the “lord of the root Pulque.” With his female counterpart, Mayahuel, he spawned the Centzon Totochtin, or “Four-Hundred Rabbits,” a group of divine rabbits known to partake in frequent drunken celebrations. This rich culture of fermentation continued for centuries until the Spanish arrived, precipitating its’ evolution into its modern form, mezcal production. While there is still a culture of pulque production in central Mexico, with several trendy pulquerias popping up in Mexico City and Oaxaca City, using this process of fermentation to distill mezcal has spread throughout Mexico, with over twenty states now possessing a mezcal culture.

*Photo courtesy of Joanna Pinneo, Dog Star Images

Fermentation in Mezcal

After being brought down from the mountains and canyons where they grow, agave are roasted in order to convert the starches in the pinas into simpler carbohydrates (sugars), making it easier for the yeast to break them down and metabolize. After cooling for several days, the agave are then crushed, pressed, or milled in order to release the juices that hold these sugars. The mixture of fiber and juice are loaded into large fermentation vats, sometimes as large as 10,000 liters, but the fermentation vessels used by our mezcaleros are between 900 - 1600 liters by volume. It is important to note that many modern, large-scale mezcal producers will strain out their agave fibers after being crushed in order to increase their yield and allow the mosto (fermenting mix of water, agave nectar and fiber) to be pumped to different areas of the palenque. However Vago, like all traditional mezcaleros leaves the agave fiber to be fermented with the mosto. The result is a more labor-intense process, as it all has to be moved by hand, but a richer, more complex flavor that basically blows up in your mouth with flavors of roasted agave, caramelized sugar, roasted fruit, flowers, vegetation, earth, and freedom.

It is in these vats that the magic begins to happen. Yeast. Its all about yeast, people. Nature’s magic dust that transforms sugars into alcohol. Traditional and ancestral mezcales must use natural yeasts; microbes that are present in the ambient environment, just floating along like Spicoli in Fast Times at Ridgemont High. These microbes permeate the environment around the palenque. They are in the air. They are on the agave plants. They are on the wooden canoa as well as the rocks lining the tahona. They are living in the nooks and crannies of whatever vessel is being used to ferment. It is because they can live in these crevices that your fermentation vessel and method can really come into play, which we will talk about later.

*Photo courtesy of Joanna Pinneo, Dog Star Images

Checking Fermentation Temperature

Once the yeast begin to eat the sugars in the mosto, they begin to give off energy in the form of heat. They also begin to give off gas in the form of carbon dioxide. This process will continue for as few as 1 or up to several days, as the yeast begin to consume all the available sugars. During this time it is constantly being monitored by the mezcalero for heat and smell. To do this, they create a large hole in the densely packed agave fiber and insert a tree limb in order to probe what the environment is like at the bottom of the fermentation vat. After a minute or two, they pull the limb out and grab it with their hand. In this short time, the limb has come to the same ambient temperature as the bottom of the fermentation vat. You can actually feel the heat that is at the bottom of the tank; the energy that the yeast give off as they happily munch away and multiply. They are also constantly smelling the mosto as the aromas of sweet roasted agave dissipate and the smells of fermentation and alcohol begin to take over.

*Photo courtesy of Joanna Pinneo, Dog Star Images

Ready For Water

Eventually, after a period of usually one to three days, the aroma of fermentation becomes so strong that one can barely stand to put their face in the vat. It is at this point that the mezcaleros say the mosto is “pidendo agua,” or asking for water. Yeast need an aqueous medium to move, reproduce and access areas of the must that contain more sugars for consumption. The water source used is yet another factor that contributes to the idea of terroir in mezcal. Aquilino uses fresh river water from the confluence of the Rio Chico and Rio Quichapa while Tio Rey has a private well feeding directly to the palenque. These water sources have their own unique mineral contents that will contribute flavor and mouthfeel to the final product. This is one of the reasons having a clean, fresh water source is so vital to producing good mezcal.

*Photo courtesy of Joanna Pinneo, Dog Star Images

Wet Fermentation

It is once the water is added that yeast start to do their work. Working in an anaerobic (oxygen free) environment, they consume the fructose and glucose (sugars) that were produced from the inulin (starch) during the roasting process. The solution begins to bubble furiously as the yeast give off more and more CO2. During this time, a crust will also begin to form that needs to constantly be monitored and broken in order to prevent acids from building up in the tepache. These acids in your tepache will translate to higher acids in the final mezcal, raising the possibility of not passing the government-mandated analyses. Some producers will actually leave the crust in tact, producing a more acidic mezcal, but our mezcaleros are very emphatic about breaking the crust, producing a softer, richer mezcal since the yeast are allowed better access to oxygen. The fermentation process produces such quantities of CO2 that the mezcaleros typically leave about ⅕ of the fermentation vat empty, to allow the tepache to expand from gas trapped below the surface. Now, some mezcaleros will allow this crust to remain, believing it has a positive effect of the final profile of the mezcal, but all three of Vago’s maestros prefer the lower acidity produced by periodically breaking said crust. However, as Tio Rey constantly reminds us, each producer has their own style and technique not necessarily better or more correct than another.

*Photo Property of Francisco Terrazas

Crust Ready to Break

As the the yeasts continue to produce alcohol, the sugars continue to drop as they are consumed for fuel. Throughout this process, the mezcalero is continually monitoring the sugar levels through taste and smell. They use a long piece of hollow reed that has had a segment carved out of the outer lining. This serves as a sort of plunger with a vessel at the end, useful for taking a sample from the bottom of the fermentation vat. As fermentation progresses, the must continues to remain sweeter the further down the vat a sample is drawn. When there is no trace of sweet agave flavor at the bottom of the fermentation vat, having been replaced by a sour, lightly alcoholic flavor, the tepache is ready to be distilled. While we at Vago have never analyzed our tepache prior to being distilled, studies of the tequila industry have shown that alcohol concentration is usually between 4% - 9% ABV, with sugar levels having been reduced from between 4-11% to ~ 0.4%

Yeasts in Agave Fermentation

Yeasts are microorganisms that are classified as part of the fungus family. They are responsible for so many of the unique flavors in things that we eat and drink. From San Francisco Sourdough to Belgian Lambic, location specific yeasts have helped give identity to so many regional specialties.

As in beer brewing, winemaking, and breadmaking, Saccharomyces Cerevisiae (Brewer’s Yeast) is the most common yeast found in the fermentation of agave sugars. S. Cerevisiae is also known as Ale Yeast, which makes sense as ales are typically brewed in warmer climates and S. Cerevisiae is active at warmer temperatures. Since S. Cerevisiae is a “top-fermenting” yeast, it does not sink to the bottom as fermentation is taking place. This is what causes the crust at the top of the fermentation vat that we mentioned before.

As we mentioned before, there are thousands of various yeast strains present throughout the world. This diversity is no different in mezcal palenques. As such, there are different yeasts present in different palenques throughout Mexico, with some overlap as some strains grow in multiple environments or associated with certain agave varieties. The mix of yeasts can even evolve throughout a given fermentation. These yeasts are responsible for many of the volatile, organoleptic compounds found in mezcal that give the tastes and aromas associated with the spirit. There are also bacteria present throughout the process that produce compounds like acetic and lactic acid. Yeast also produce a litany of enzymes that liberate other compounds known as terpenes that are present in raw agave as parts of other complex carbohydrates. These terpenes, once released, also function as organoleptic compounds (P. Lappe-Oliveras, et al. 2008).

A chart of different microbes found in samples taken from the production of different agave spirits in different states can be found by clicking on the link below:

Chart from P. Lappe-Oliveras, et al. 2008

It is important to note that while studies like P. Lappe-Oliveras, et al. (2008) have found links suggesting correlation between certain yeast strains and enzymes to specific volatile, organoleptic compounds, further research is needed to establish a causal link between specific strains and corresponding compounds.

Fermentation Vessels

Pit

The most primitive method of fermentation are pits dug directly into the ground, sometimes into the soft earth with soil serving as the lining or directly into bedrock. They have been used throughout the world for fermentation of different alcoholic beverages as well as fermented food. In China, microbial analysis has been done on alcohol fermentation pits that have been in continuous use for 440 years, while cultures in central Africa use banana leaf-lined pits to ferment banana beer. Ancestral fermentation pits of the Huichol/Tarahumara culture have been found near Guadalupe Ocotan, Nayarit where agave were fermented as a substitute base for Tesgüino; since the maguey was cooked, it would be a cross between a Tesgüino and a tepache rather than a pulque. Further to the north, in the Urique Canyon region of the Copper Canyon in southwestern Chihuahua, the Tarahumara are still fermenting Lechuguilla agave in small pits dug into bedrock to be processed for mezcal. (Tarahumara Lechuguilla Mezcal Fermentation Pits, Copper Canyon, Chihuahua) There are also bedrock fermentation pits in Tecuana Canyon, near Amatitán in central Jalisco, remnants of one of the first tequila distilleries.

While very limited analysis has been done on the microbiota of pit fermentation systems, there would no doubt be different microbes present in different concentration in different environments (organic vs. inorganic, soil vs. rock, etc.). In turn, these different microbes would likely produce their own unique mix of enzymes and compounds that would result in varying acids and organoleptic compounds that would produce different flavor and aroma profiles in the final distillate.

Translation: These are very rudimentary and old systems. The people that use these techniques have never really considered yeast or enzymes or even know what microbiota means. We at Vago had to google it. Nor could we find any studies that talk about what yeast are growing in the soil of central Africa. The one study we could find showed that there were indeed different mixes of microbes in Chinese fermentation pits, and that’s about as deep as they went. That said, knowing the limited amount that we do about yeast, terroir, plants, etc., it seems pretty damn obvious that different soil (due to mineral content, organic matter, etc.) in different areas in direct contact with a live, fermenting beverage are probably going to produce different flavors.  While it is not very common in any commercially available mezcales (we have yet to taste one), there are small areas of indigenous people that are still practicing this ancestral method.

*Photo Courtesy of Almamezcalera

Bovine

Another ancestral fermentation method can best be as …. utilitarian in nature. Mezcaleros will take a hide from a bovine and suspend it within a rectangular wooden frame, using that as their fermentation vessel. They crush their roasted agave and fill the hide with agave and water and allow it to ferment, typically with ambient yeasts, sometimes uncovered or topped with palm fronds. While there is a large potential for microbial variances within each cowhide, there have been no conclusive studies that we could find that have discussed the microbiota in bovine hides and how they affect the final flavors of mezcales fermented in them.

Translation: We at Vago have never experimented with fermenting in cowhide. Its raw, its funky,  its super old school and its hella-badass. We’ve experienced some such mezcales from Sonora, Puebla, Oaxaca and other states and we can definitely describe them as different. Like Pechugas, they never actually taste like meat. However, they do typically seem to have a dry, dusty and almost leathery mouthfeel on the finish that dries out the palate as the finish lingers. It is a much more textural experience than a flavor one. If you ever find yourself with a leather-fermented mezcal on the bar in front of you, F’ING DRINK IT!!!

*Photo Courtesy of anilmezcal.wordpress.com

Ceramic

Ceramic is one of the most traditional and well documented, ancestral vessels used for fermentation. It is in fact ceramic shards that were unearthed in China providing evidence of fermentation dating back 10,000 years. In Mexico, Spanish settlers discovered native peoples were already drinking beverages that were fermented in ceramic. However, there is evidence from pottery shards found in burial sites in Colima as well as the “los Bebedores” mural in Puebla which suggest agave was being purposefully fermented as early as 200 CE (Common Era) or earlier. There are some mezcaleros, predominantly in the area north of Oaxaca City, in the Mixteca Alta, who are still fermenting in ceramic.

Ceramic fermentation presents its own specific set of advantages and disadvantages. First, it provides a greater level of temperature stability than stainless steel or plastic, but not as much as a large wooden vat. They are also more mobile than stationary fermentation pits dug into dirt or bedrock. Like vats dug into organic material, clay fermentation vessels are likely to host an ever changing set of microbes that can affect the final flavor of the mezcal, as well as leech minerals into the fermenting tepache. However, ceramic is obviously very fragile and can be damaged during transport, accidental contact, or even rapid temperature change. They are also of a smaller volume, usually around 40 l. versus wood or stainless steel vessels that can be between 1,000 & 10,000 l.  Because of this smaller volume, fermentation will be quicker and will require lower temperatures and closer monitoring in order to produce the more complex flavors that are so prized in agave distillates. In short, while requiring more care and attention, the evolving environment of the clay due to microbes and mineral content can produce some truly stunning mezcals that have the potential to be more complex than those fermented in plastic or stainless steel.

*Photo courtesy of Joanna Pinneo, Dog Star Images

Wood

Wood is by far the most common material used for fermentation in traditional mezcal production. All three of the Vago palenques use Sabino wood, a type of pine tree that is native throughout much of Mexico. Our fermentation vats vary from between 900 l. to almost 1,700 l. Some are large cylindrical vats constructed of planks of wood bound by wire and strips of metal, but Tio Rey actually has one fermentation vat that is a hollowed out Pine trunk that has been in use for over 100 years.  The planks of the standard cylinder vats provide the benefit of being easily interchangeable if one is cracked or otherwise damaged. However, the vats themselves are very difficult to move once they have been constructed in the palenque. Fermentation vats are much more temperature stable than clay due to their size as well as lower thermal conductivity of wood. This means wood provides a slower, lower temperature fermentation during the warmer spring and fall months, and provides insulation during the cold winter months.

Since wood is an organic material with a porous surface, they are more difficult to clean than plastic or stainless steel and like ceramic, it is a better environment for yeast and other microbes to flourish between fermentations. This means that the environment will continually be evolving, providing differences between batches. From a consistency perspective this can obviously cause problems, but these variances are one the of the factors that are so prized by mezcal enthusiasts.

Stainless Steel

In larger scale modern operations, some mezcaleros have made the transition to stainless steel as their fermentation material. It provides several benefits, most of which allow for faster fermentation, higher yield and a more consistent product. When considering these benefits, it is understandable why some operations are moving in this direction. Since they can be completely fabricated to specification, they can be made in larger capacities (think 10,000 l.), allowing for larger batches. They can also be modified with insulators and water systems that allow the temperature to be more precisely controlled. Stainless steel is also a nonporous surface, which means there is no passage in and out of  the vessel wall by fermenting mezcal; stainless steel does not “breathe” or expand and contract with the temperature the way that ceramic or wood do. It can also be built as a covered vessel with an removeable cap, so that the fermented can be protected from the ambient environment. This allows for a much more controlled exposure to microbes, creating a much more consistent fermentation with a more controllable flavor profile.

While these aspects of stainless steel obviously lend themselves to a more efficient operation, many mezcal enthusiasts feel as though it lacks the authenticity and tradition that makes mezcal so unique. Because stainless steel is considered a “cleaner,” more controllable technique, the mezcales produced with this method are often considered more predictable and simple than those produced using wood or other traditional methods.

Plastic

Another common and more economically viable technique is to ferment in plastic vats. Sometimes these are Rotoplas containers that are often used to store drinking water, while sometimes they are large 2500 l. vats that resemble large garden planters. These plastic vessels are often inexpensive, being offered by a government subsidy to help mezcal producers enter the market. Besides being inexpensive, they are also very durable in contrast to clay pots and are very easy to move around the palenque. Because of the government assistance available to procure these types of containers, they are often the vessels used by first time, inexperienced mezcaleros. There are some dangers involved with these technique, acids in the tepache may leach chemicals from the container walls if it is not the right type of plastic. These can lead to undesirable compounds in the final product, producing off flavors or even being toxic. However, luckily most traditional, trusted producers have eschewed these plastic containers in favor of the more traditional wooden vats.

Plastic vessels can also be easily sterilized, meaning that like stainless steel, they lack the microbiotic environments present in materials like clay, wood, and leather. This more sterile environment will cause a lack of complexity as there are fewer yeast and bacteria present to produce those volatile compounds.  

Translation: While it is common to see plastic fermentation vats due to their being relatively inexpensive, it is NOT a traditional production technique. You are not getting the necessary interaction of bacteria and microbes to produce acids and aromatic compounds. Furthermore, unless you have seen production first hand, there is no way to know if mezcaleros are using safe plastics that are not giving off toxic chemicals.

A Closing Thought on Tradition

As agave culture has evolved over the centuries, particularly in mezcal production, the introduction of technology and increase in demand has caused many mezcaleros to push towards more efficient and economical means of production. We at Vago are trying to keep ourselves firmly rooted in the traditions that previous generations have taught us; the ones that have given us not only this incredible spirit, but our identities as well. From stewardship of the land to how we cut on our stills, these are the things that have been taught to us. Engrained in our families. Its not that we are afraid of innovation, we simply don’t want to dishonor those that have come before us. We are incredibly proud of our mezcal and we do not see the need to modify how we make it in order to increase our production volume. To do so would be a dishonest representation of who we are. Please understand that these articles discuss the many ways that mezcal can be made. The hand of the maker is so influential in mezcal production that its role cannot be overstated. As such, when we mention steps that we take, we can only speak to our processes. There is not any right or wrong way to make mezcal. There is traditional and nontraditional. Whichever is best is ultimately up to the consumer. We simply choose to stick with our traditions. Soy el Vago. 

Works Cited

Bruman, Henry J. Alcohol in Ancient Mexico. Salt Lake City: University of Utah Press, 2000.

Cedeño Cruz, M., Alvarez-Jacobs, J., Production of Tequila from Agave: Historical Influences and Contemporary Processes, 1999,

Gentry, Howard Scott. Agaves of Continental North America. 1982. University of Arizona Press, Tucson, AZ. p 5

Guo M-Y, Huo D-Q, Ghai R, et al. Metagenomics of Ancient Fermentation Pits Used for the Production of Chinese Strong-Aroma Liquor. Genome Announcements. 23 Oct. 2014.

Lappe-Oliveras, P., et al., Yeasts Associated with the Production of Mexican Alcoholic Nondistilled and distilled agave beverages, Blackwell Publishing, 2008.

McGovern, Patrick E. Ancient Wine: The Search for the Origins of ViticultureI. 2003. Princeton University Press, Princeton, N. J. p. 314

Patrick, Charles H. Alcohol, Culture, and Society. 1952. Duke University Press, Durham, N. C. pp 26-27