Give It a Rest! How Glass Demijohn Resting Leads to Extraordinary Mezcals

At the longtime Macurichos family palenque, located in Santiago Matatlán, the so-called “world capital of mezcal” in Valles Centrales region some 30 miles east of Oaxaca City, there is a space known as el cuarto de descanso, the “resting room.” There, several hundred demijohns — 10-gallon glass vessels — are neatly lined up on the floor, each holding mezcal that has been resting for five, eight, perhaps even 10 years.

“A freshly distilled mezcal might taste good, but you won’t fully appreciate all its flavors, so it needs to rest,” says Macurichos maestro mezcalero Gonzalo Martinez Sernas, comparing it to stabilization in winemaking. “After a while, the alcohols won’t be so harsh, and the flavors will be more intense and mature.”

(Sernas responded to my email in Spanish and this is my best translation.)

In fact, in our recent tasting of over 70 mezcals, our top two favorites were glass demijohn-rested: the Cinco Sentidos Tobalá Cultivado (Alberto Martinez), which offered an incredible pickled red onion sensation on the palate backed by some elote notes; and Sernas’s Macurichos Joven Cirial Mezcal Artesanal, which, after 30 months of demijohn resting, was heavy on the citrus notes, almost like a fresh-cracked Sprite.

“Aging is part of the Macurichos family’s tradition and philosophy,” says Sernas.

After distilling a mezcal, he ages it for a minimum of nine months in glass, though most of the extraordinary mezcals Macurichos produces are rested at least two years, while they have some on the market that stretch to decades old, some even older than Macurichos has been a commercial operation.

Why Demijohn?

Though many mezcaleros believe from pure sensorial observation that their mezcals “improve” while in glass demijohns, historically there were other reasons more important for demijohn resting.

“As these things tend to go in the world of mezcal, there is not just one single, straightforward answer,” says Jason Paul Cox, the founder of Espíritu Humano, the producers of Cinco Sentidos.

Cox explains that in some communities, mezcaleros would put a portion of their most exemplary batches in glass demijohns and then bury them underground to act as a sort of insurance policy for when economics dictated that it needed to be sold. Similarly, a demijohn collection acted as a library of a family’s distilling history. Sernas explains that he always preserves antiguas de semillas legendarias (mezcals of a legendary harvest).

But, at one time, there were more covert reasons for putting mezcal in demijohns.

Justin Briggs, Mexico portfolio manager at Skurnik Wine & Spirits, relates the story he heard of legendary mezcalero Don José Cortés burying demijohns full of mezcal in the family’s front yard whenever he knew that the taxman would be coming around, letting it rest ’til the coast was clear, and then digging it back up again. Eventually, he started noticing that the extra time resting in a cool, dark place had evolved the mezcal’s profile quite a bit.

“Let’s remember that this drink is considered sacred by the Zapotec people of Oaxaca, used in rituals, offerings, ceremonies, or as part of traditional medicine,” says Sernas. “But we must also remember that from its origin, it has been a drink of the people, made in villages, at home, with family, in a very artisanal or homemade way, often with great poverty.”

Resting in Europe

Of course, glass demijohn resting is not solely a mezcal thing. Historically, they have been used in various spirits categories as storage vessels.

The earliest uses of demijohns dates back to perhaps the 17th century, which aligns with the rise of commercial distillation in Europe. Initially, it would have probably been brandies put into demijohns — often wrapped in wicker — for storage and transportation in the Atlantic trade. You would eventually also see demijohns in the rum world, most notably in the British Royal Navy rum rations.

“From a chemical standpoint, it is true that demijohn resting allows for micro-oxidation, as the corks that most producers are using to seal the demijohns are far from airtight.”

Eventually, demijohn usage became not just about storage but about resting and refinement as well. In the Italian world of grappa, demijohn resting is a long-held tradition, with producers resting the pomace spirits for several months to even a few years before bottling to allow the fiery, raw distillate to soften into something more palatable. The same holds true for the many eau-de-vie producers in places like Austria, Switzerland, and Germany where spirits made from fruits like pear, apricot, or cherry are rested in glass to preserve their bright aromatics while still giving the spirit time to become more cohesive.

Eventually, these storage and resting techniques would cross over to the world of mezcal with producers putting their spirit in whatever vessel they had around. That might mean carboys, garrafones (water jugs), clay pots, wooden barrels, and, eventually, damajuanas or demijohns.

“I guess I haven’t seen anything that’s conclusively archeological, like, this is the exact origins of demijohn usage in Mexico,” says Briggs. “But what I hear a lot is that glass aging arose many, many decades ago when mezcal was, for the most part, kind of kept in the shadows like a moonshine or something.”

While Resting

Whatever the humble origins, these days, mezcal has become a connoisseurial spirit and demijohn resting clearly seems to improve its quality in a way the cognoscenti prefer, even if they can’t exactly explain what is happening.

Briggs compares immature mezcal to a person showing up at a party where they don’t know anyone — it will take them a few hours (and a few drinks) to integrate with strangers.

“The volatile compounds are doing the same thing,” he says, mentioning those off-putting acetone nail polish remover notes. “You have this new batch of mezcal and it’s rough around the edges, but then it sits in glass and interacts with oxygen and softens and finds itself.”

The entire spirit becomes mellower with aromas and flavors more fruit-forward with accentuated floral characteristics — more nuanced notes that can become easily masked by big volatile compounds at the start.

In fact, Sernas explicitly likes to leave a lot of those volatile compounds in his mezcal while keeping it very high-proof in anticipation of letting the glass-rested mezcal slowly shift and evolve with oxygen interaction. Indeed, other mezcaleros I spoke to believe mezcals made with their own “tails” age better than those diluted with water, since their organoleptic complexity is greater, which can lead to more richness after resting.

If I’ve long been told that spirits can only change when aged in wood — taking on tannins and wood sugars — that is clearly not the case if you taste demijohn-rested mezcal. Likewise, while writing and researching my book “Dusty Booze: In Search of Vintage Spirits,” I was constantly told that, once bottled, a spirit becomes a sort of liquid time capsule, tasting the same way today as it will decades from now. That is also clearly not the case when it comes to demijohn aging. There is absolutely something about resting a spirit in gigantic glass vessels, as opposed to simple 750-milliliter bottles, that creates an appealing change in its aroma, flavor, and texture.

Briggs fully believes it is due to how much oxygen is let into the demijohn, telling me that some mezcaleros specifically choose not to seal these vessels particularly well.

“From a chemical standpoint, it is true that demijohn resting allows for micro-oxidation, as the corks that most producers are using to seal the demijohns are far from airtight,” adds Cox.

Buried in Glass

Where the demijohns are resting seems to matter, too.

Orlando Estrada, co-founder of Tlamati, talks about the tradition in several parts of Mexico including Puebla, Guerrero, and Michoacán, of “improving the mezcal” by burying it in glass; it’s something Tlamati maestros mezcaleros Sergio and the late Balbino Salas have long done using 19-liter glass containers covered with a piece of “olote” (the heart of a native corn cob).

“When mezcal is buried, we say it helps it harmonize better, gaining smoothness and sweetness, developing a more stable ‘pearl,’ and generally becomes a mezcal for a special occasion when it’s unearthed — weddings, baptisms, quinceañeras, etc.,” says Estrada.

(He notes that unearthing this buried mezcal is quite risky, however, as the pick and shovel must be handled with great care as even a minor misstep can cause the jugs to shatter and the mezcal to be lost.)

Estrada has found that with mezcals buried in glass, the esters increase, the pH, furfural and aldehyde levels decrease, and the flavor improves, with a hint of corn even appearing.

A few years ago, Cox took a small batch of mezcal and put it into demijohns, some of which he stored in a dark, cool place, the rest of which he buried underground. A year later, he drew samples from both sets of demijohns and sent them to a lab.

“What I hear a lot is that glass aging arose many, many decades ago when mezcal was, for the most part, kind of kept in the shadows like a moonshine or something.”

While the buried mezcal retained the same ABV, the above-ground mezcal had lost proof and dropped in both superior (fusel) alcohols and methanol. Flavor-wise the underground batch had lots of dark green tones with a wintergreen and forest floor element. But the above-ground mezcal was now aromatically bright, with notes of cantaloupe among a fruity palate and rich mouthfeel.

“A few months to a few years of this type of resting allows for more volatile components to slowly burn off, as well as the formation of esters, which tends to lead to a creamier, oilier mouthfeel with time,” says Cox. “This coincides with the ‘softening’ or rounding sensation that mezcaleros will describe as a result of demijohn resting.”

Essential to Rest

As mentioned earlier, our top two mezcals on this year’s list were demijohn rested. Our top tequila was likewise, a Tequilana weber destilado de agave from Tlamati. That’s probably not a coincidence. As more and more agave spirits brands lean into more ancestral and artisanal techniques, demijohn resting seems like perhaps the final step in the production process.

Likewise, if “tahona,” “earthen oven,” and “puntas,” have become buzzwords in agave over the last few years, maybe “demijohn rested” will be the next to hit the marketing wizards, though Briggs claims this is not something that is yet on the radar of most consumers.

“Like a lot of things in mezcal, there are a small amount of people who are really paying attention to the details,” says Briggs, who notes that when he does tastings with agave clubs or at agave-centric bars, there are definitely people who sit up and take notice when he mentions demijohn aging. “But it’s not so common yet for me to have normal people walk in asking for it.”

But it doesn’t matter how many “normal people” know about it. Because, for Mexico’s best mezcaleros, there continues to be no doubt about how they are going to mature their spirit.

As Sernas says of demijohn resting:

“It is absolutely essential!”

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