Carvajal, who already had experience recovering other yeasts, found out about the ancient Franciscan brewery in Quito while reading specialist beer magazines.
It took him a year to do so, but he finally managed to find a barrel from the old brewery in 2008.
It was stored in Quito's San Francisco Convent, an imposing three-hectare complex built between 1537 and 1680, which is now a museum.
After extracting a splinter, Carvajal used a microscope to find a tiny yeast specimen, which after a long period of cultivation he was able to resurrect.
In his laboratory at the Catholic University of Ecuador, Carvajal takes a small vial containing a variety of the Saccharomyces cerevisiaerescatada yeast.
"It lives here in a little container. It's very humble, but it is the star" of the laboratory, said the 59-year-old.
Filling the holes
Carvajal, who comes from a brewing family, found an article in an industry magazine that vaguely described the formula for the Franciscans' 16th century drink.
Little by little, he pieced together bits of information to revive the brew with cinnamon, fig, clove and sugarcane flavors.
"There were a massive number of holes in the recipe and my job was to fill those holes," said Carvajal.
"It is a work of beer archaeology within the microbial archaeology" he had to carry out to rescue the yeast, which generates the majority of the drink's flavour.
After a decade of investigation and testing, Carvajal in 2018 began producing the beer at his home -- but the pandemic frustrated his attempts to commercialise it.
He still has not come up with a launch date for his product, nor a price.
Carvajal compares his work, centuries after the Franciscans domesticated the yeast, to intensive care on a molecular scale.
"It is as if they were dormant, like dried seeds but having deteriorated over the years. So you have to reconstruct them, fluidise them, hydrate them and see if their vital signs return."
Historian Javier Gomezjurado, who wrote a book on Quito beverages, told AFP that the brewery in the San Francisco Convent was the first brewery in hispanic America.
It began operations in 1566, but there were just eight friars in the convent at that time and production was minimal, said Gomezjurado.
With the introduction of machinery into the brewing industry, ancient formulas began to disappear. The brewery closed in 1970.
For Carvajal, resurrecting the yeast and the age-old methods used to make the ancient recipe was simply a labour of love for "the value of the intangible."