Masa ( /ˈmɑːsə/; [ˈmasa]) is Spanish for dough. Although the word is mostly used to refer to any kind of dough, in some regions (Mexico, parts of Central America and the American South West) it is often short for masa de maíz, a maize (corn) dough made from freshly prepared hominy. It is used for making corn tortillas, tamales, pupusas, and many other Latin American dishes. The dried and powdered form is called masa harina, masa de harina, and sometimes Maseca, the name of a leading commercial brand. It is reconstituted with water before use. Masa is not to be confused with masarepa, masa de arepa, or masa al instante, a type of unnixtamalized, soaked, and cooked cornmeal used to make arepas. Masa de trigo is Spanish for wheat flour dough. It is also used for making wheat tortillas and other breads and pastries.
To make hominy, field corn (maize) grain is dried and then treated by soaking and cooking the mature (hard) grain in a diluted solution of slaked lime (calcium hydroxide) or wood ash, a process termed nixtamalization. Lime and ash are highly alkaline: the alkalinity helps the dissolution of hemicellulose, the major glue-like component of the maize cell walls, and loosens the hulls from the kernels and softens the corn. Some of the corn oil is broken down into emulsifying agents (monoglycerides and diglycerides), while bonding of the corn proteins to each other is also facilitated. The divalent calcium in lime acts as a cross-linking agent for protein and polysaccharide acidic side chains. As a result, while cornmeal made from untreated ground corn is unable by itself to form a dough on addition of water, the chemical changes in masa allow dough formation, which is essential to the ability to fashion dough into tortillas.
Finally, in addition to providing a source of dietary calcium, the lime reacts with the corn so that the nutrient niacin can be absorbed by the digestive tract. While consumption of untreated corn is a risk factor in predisposition to pellagra, as in African countries, the risk is dramatically reduced or eliminated by nixtamalization. The soaked maize is washed, and then ground into masa. When fresh masa is dried and powdered, it becomes masa seca or masa harina.
The process of making hominy is also called nixtamalization and the ground product can be called masa nixtamalera. In Central American and Mexican cuisine, masa nixtamalera is cooked with water and milk to make a thick, gruel-like beverage called atole. When made with chocolate and sugar, it becomes atole de chocolate. Adding anise and piloncillo to this mix creates champurrado, a popular breakfast drink.