The Obscure Sauce That Is Changing Indigenous Economies in the Amazon, a great article written by Nick Gill and published in the New Worlder.
"In the Amazon Basin, an ancestral sauce made from the fermented extract of yuca, something once believed to have no monetary value, is changing indigenous economies.
"Called a handful of names from tucupí preto and ají negro to casaramá and ualako, indigenous communities around the region pass down recipes from generation to generation.
"To make it, yuca brava (Manihot esculenta), the poisonous form of yuca or manioc, is peeled and soaked in water for several days. After the juice separates from the starch, which gets used in bread, and boiled, it becomes tucupí, a sour yellow juice used in traditional dishes like tacacá and pato no tucupí (boiled duck with tucupí) in the Brazilian state of Pará. When it is further reduced it becomes tucupí negro, which was mostly unknown outside of indigenous communities until a few years ago."
Brush black tucupi on meats or use a drop to compose a sauce with a unique umami flavor, something sweet, salty, acid, and smoky. It makes a good substitute for soy sauce.