The phrase "starch grains" refers to tiny particles of a substance called starch. Starch is a type of carbohydrate found in many plants, like potatoes or rice. These grains are small and can be seen under a microscope. Full definition
The high quantity of starch grains cook to a light, fluffy texture and full, firm appearance when properly prepared. (idahopotato.com)
In 2005, a team led by Piperno and Anthony Ranere, an anthropologist at Temple University in Philadelphia, Pennsylvania, hit pay dirt: Under a giant boulder in the Balsas River region, called the Xihuatoxtla Shelter, the researchers discovered a trove of prehistoric grinding stones to which phytoliths and starch grains from maize were still adhering. (sciencemag.org)
In 2010 scientists found surprising evidence of starch grains on crude mortars and pestles at sites in modern - day Italy, Russia and the Czech Republic. (scientificamerican.com)