Masa (; Spanish pronunciation: ['masa]) is a corn dough or flour (masa harina) that has been soaked and cooked in an alkaline solution in the nixtamalization process. It is used for making corn tortillas, tamales, pupusas, and many other Latin American dishes. Its full name is masa de maíz and the dried and powdered form is called masa harina, masa de harina, and sometimes Maseca, the name of one commercial brand. The flour is reconstituted with water to make a dough before it is used in cooking.
In Spanish, masa harina translates to "dough flour", which can refer to many other types of dough.
Field corn 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. This process is nixtamalization, and it produces hominy, which is ground into flour to create masa harina.
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. 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 chemical changes in masa allow dough formation, and also allows the nutrient niacin to be absorbed by the digestive tract. By contrast, untreated cornmeal is unable to form a dough on the addition of water, and a diet heavily reliant on its consumption is a risk factor for pellagra.
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.