The spinach , also called canastro , caniço or horreo, is a normally of stone and wood structures , there are however some entirely of stone , with the function of drying the coarse corn through lateral cracks , and at the same time to prevent the destruction of the same by rodents by raising this . As corn requires to be harvested in the fall, this needs to be as airy as possible to dry in such adverse season as winter. In mainland Portugal , are mainly the north, particularly in the regions of Minho, Beira Litoral, Beira Interior and West of Tras -os- Montes .