Produced from the sap of the maguey plant, pulque advocates say the drink has medicinal qualities but worry that beer and other standard beverages are pushing it aside.
Beer drinkers can find pulque's taste off-putting and no advertising campaign has been undertaken to promote the drink, said Epifanio Leyva, who runs La Botija, a pulque bar or pulqueria in the Mexican capital.
"For 15 years the consumption of pulque has fallen, due to a lack of advertising by the big bars," Leyva said.
"At this rate, it's likely that the next generation won't be acquainted with it," said Leyva.
Once, 20 trucks would arrive to deliver pulque in the popular Xochimilco quarter every three days, he said. "Today, sad to say, no more than two trucks come," Leyva said.
Five pulque bars operate in the district, where there were once 18 pulquerias.
The milky beverage, with a low alcohol content, is served neat or with a taste of honey or fruit. Known as "octli" in the indigenous Nahuatl language, pulque has been a mainstay for workers who do not frequent the city's chic bars.
Pulque fans say the drink's status came under attack years ago when the beer industry is said to have spread rumors that the drink was fermented from the feces of amimals or humans.
Pulque is really made from the fermented sweet sap of the maguey plant, which is also the source for mezcal -- a more potent liquor produced from the heart of the plant instead of the sap. Tequila comes from another type of agave plant.
References to pulque date back centuries in pre-Hispanic Mexico, generating folk tales and myths. Aztecs were believed to use pulque for religious rituals and worshiped a god of pulque.
At Levya's bar, a glass of pulque goes for 10 pesos (less than a dollar/euro) and is served with maize tortillas with a spicy salsa.
"You can drink one or two, eat three or four tortillas and you have a meal. Pulque is very nourishing," said Pablo Flores, a stout man with a passion for pulque.
"It gives strength to women after childbirth, helps produce milk in breastfeeding mothers and makes them want to have more children," said a smiling Flores, a regular at La Botija.
Ana Pablo, 55, who works as a dishwasher at a restaurant, prefers pulque to beer "because it doesn't make you sick and there is no hangover the day after."
Her brother was advised to take pulque for his diabetes, said Pablo, before draining her final drink of the evening.
To the relief of La Botija's owner, much of his bar's clientele is young.
"At first, I didn't like the texture," said 21-year-old Saria Fuentes, "then I got used to the taste and now, I love it. And it doesn't give you a hangover. What more can you ask for."