Sour cassava flour (Polvilho azedo)

Polvilho azedo, also known as sour cassava flour or sour tapioca flour, is a type of Brazilian flour made from fermented cassava roots. To produce polvilho azedo, the cassava roots are first peeled, grated, and then soaked in water to remove toxins and starch.

The resulting pulp is then squeezed to eliminate excess moisture. The moist pulp is left to ferment for a period of time, typically around one to three days, allowing naturally occurring microorganisms to break down the starches and convert them into organic acids, which give the flour its sour taste.

After fermentation, the pulp is dried and finely ground to obtain polvilho azedo. The resulting flour is slightly acidic, hence the name "azedo" (meaning "sour" in Portuguese). It has a distinct flavor and is commonly used in Brazilian cuisine to make various traditional dishes such as pão de queijo (cheese bread), tapioca crepes, and bolos (cakes).