After natural fermentation and solar drying, sour cassava starch acquires expansion property. Traditionally, solar drying occurs without protection, and consequently physical contamination can arise. Thus, the aim of this study was to produce sour cassava starch using a low-cost solar dryer to prevent contamination, whilst retaining the expansion property. The samples were characterized in relation to chemical composition, microscopy and physical contaminants, as well as expansion, thermal, pasting, structural and technological properties. In addition, biscuits were prepared and compared with commercial samples. The solar dryer provided faster drying and lower moisture levels than the control. The specific volumes of the sun-dried products were similar to the control, with minimized contamination. The granules of the starches showed slight erosion on their surface, which was probably due to amylolytic enzymes. X-ray diffraction showed a typical A-type pattern. DSC analysis resulted in higher gelatinization temperatures and enthalpy changes for the sour cassava starch. The pasting properties showed a reduction in the viscosity peak at neutral pH. Although the cassava starch biscuits made with sour cassava starch dried in the solar dryer presented lower expansion levels in relation to the other biscuits produced with commercial sour cassava starch, they had desirable sensory characteristics.