Drive into the agricultural village of San Luis Soyatlán on the southern shore of Lake Chapala, Mexico's biggest inland body of water, and you will soon spot dozens of people walking around and clutching plastic bags full of crimson liquid, as if an entrepreneurial vampire had set up shop there to supply his brethren with their daily doses of blood at a very reasonable price.
When I arrive one scorching Sunday afternoon, there are already some 50 people queuing anxiously to get their fix from a stall by the side of the road. There is only one thing that compels them to stop in this otherwise unremarkable town: its status as the birthplace of the vampiro, arguably the greatest tequila cocktail in all of Mexico.
Oscar Hernández, a portly local resident with a creased face and graying hair, claims to have invented the drink almost 40 years ago, during his daily shift selling seasoned cucumbers and jicama at his roadside stand. "I used to prepare these drinks for myself to keep cool in the heat, but customers would arrive and ask what they were," he tells me. "It looks like you're sucking up blood when you drink one, so I decided to call them vampiros."
Hernández's customers soon began asking if he would prepare them one of his strange red drinks. At first he decided to give them away for free in a bid to keep his clients coming back to his fruit stand. Few travellers used to come through town back then, he explains, so he saw the vampiros as nothing more than a means of keeping regular clients happy.
Then, as the drinks became more popular, he saw an opportunity to commercialise them.
"People started drinking two or three each time they came, so I decided to start selling them," he says. "I used to sell them in cups but these would spill in people's cars, so I started selling them in plastic bags. It's practical and cheap and our customers like it that way."
Founded by indigenous Chichimeca Indians before the Spanish conquest of Mexico, San Luis Soyatlán is home to approximately 3,000 inhabitants. Surrounded by miles of scrubland, it is located on the highway between Guadalajara, Mexico's second biggest metropolis, and Mazamitla, a mountainous retreat where many city dwellers come to rent cabins in the cool pine forests each weekend.
With word of Hernández's magical cocktails gradually spreading over the years, the town has become an almost compulsory stop-off point for a mid-journey refreshment. "Vampiros have only started becoming really popular in the last eight years," Hernández says. "Most of our customers are young people on their way to Mazamitla, including children who like to drink them without liquor and just enjoy them because they're tasty and refreshing."
Many places sell vampiros now, but thanks to word of mouth, Hernández's stand remains the most popular in town. (He has defiantly chosen not to name the establishment, but it can be found between Calle Aldama and El Retiro street on the highway from Guadalajara.)
Having perfected his recipe over the years, Hernández's vampiros are made with ice; lime juice; salt; freshly squeezed orange juice; Squirt, a hugely popular Mexican brand of grapefruit soda; and homemade sangrita, a zingy blend of orange juice, tomato juice, chile, lime, and salt. Customers can then add their choice of Cazadores, Centenario, Herradura, Tradicional, Tequileño, or Pueblo Viejo tequila.
As the queue advances, customers pass several different members of Hernández's team—many of them close family members—each tasked with pouring a different ingredient into their transparent bags, which become heavier and more colourful with every step forward.
The biggest servings come in huge bags holding over a litre, while the prices range from 30 to 80 pesos (£1.13 to £3.02) depending on the size of the bag and whether or not it contains tequila. The bags are tied around a straw so you can suck up their contents without the risk of spilling it everywhere.
Having finished his explanation of the drink's history, Hernández hands me an expertly bagged vampiro with a serious look on his face that masks his pride at his creation. It is an immensely satisfying beverage: sweet, sour, and salty, with a light kick to it. Perfect for a hot summer's day in the Mexican countryside.
What better way to put your hometown on the map?
Follow Duncan Tucker on Twitter: @DuncanTucker