While maize is consumed in many forms including roasted whole seed pods (elotes), most maize cuisine is based on masa a moist dough prepared from pulverized maize seeds. Traditionally masa is prepared by soaking dried maize seeds overnight in a weak basic (-OH) solution produced by dissolving lime (CaO) in water. This causes the dried seeds to swell and become soft making them easier to grind with a mano and metate. More importantly, the alkali solution produces a chemical reaction in the seed material which significantly enhances the nutritive value of the seeds to humans.
More specifically, maize seed is deficient in nutritionally essential amino acids: lysine, tryptophan and niacin. Soaking in the basic solution, while it lowers the overall nutritive value of maize, selectively enhances the relative amounts of these essential amino acids available to the human digestive process. Without this processing, relying on maize alone as a source of these amino acids would result in considerable malnutrition, especially among young children. One manifestation of this would probably be a high incidence of pellagra due to niacin deficiency ( Katz, et. al. '74).
After soaking in the basic solution, the seeds are ground, the hulls removed, and the resulting moist, somewhat coarse paste is masa.
Masa, prepared in this manner, can be diluted with water and consumed as a gruel, possibly with something like honey added to enhance the flavor. It can also be used in the preparation of tamales -- a cylinder (about 10 cm long 3 cm in diameter) of masa surrounding a filling consisting of some combination of beans, chopped meat and vegetables (e.g. chiles) wrapped in maize husks and baked or steamed.
The most common use of masa is in the preparation of tortillias the staple food in Mesoamerica since the Middle Formative Period. Tortillias are flat, unleavened maize cakes, 12 - 24 cm in diameter, prepared from masa traditionally cooked like pancakes on a ceramic grill ( comal).
Tortillias, like uncooked masa, are moist and will become moldy after a couple of days. Careful households (and restaurants) consuming tortillias prepare (or procure) them fresh each day. But, with a little more cooking, they become crisp and completely dry tostadas. Tostadas can be preserved indefinitely and transported in nothing more elaborate than a cloth bag, making them an ideal “snack food” for travelers and workers in fields remote from their residence.
The preparation of masa described above is one of several maize preparation procedures employed by people in the New World before European contact. Most of these involved exposing the maize seeds to a basic solution in some way or other. The source of the -OH ion varied. Lime (CaO) was most common in Mesoamerica and the and provided nutritionally important calcium as well. Elsewhere potash (K2CO2OH) from wood ashes and "lye" (its not really clear what the authors mean by 'lye', possibly Na2CO2OH) was employed. Some groups (Lacandon Maya) add roasted, pulverized fresh water mussel shells to the water in which maize seeds are boiled. Others (Yucatec Maya) possibly used snail shells in the same way. Still others may have “deliberately” selected grinding stones with high lime content. (See Cushing '‘20.) for a description of the Zuni’s procedure for choosing material for metates.) A survey of ethnographic records reveals a significant correlation between degree of dependence on maize for food and use of a basic solution in it’s preparation ( Katz, et. al. '74).
How did all these people figure out that soaking maize in a basic solution enhances it nutritive value? It’s pretty clear they didn’t design their food preparation technology using the knowledge of biochemistry we use to describe the phenomenon. If you ask people why they prepare maize in this way, you get different answers. Most say that it softens the hulls; some go further to say it aids the digestive process and prevents constipation. I was told personally by a vendor of limestone pebbles (among other things, including culinary herbs) in the market in Cuernavaca that their use in the cooking of maize improved the flavor.
It may be just happy coincidence that good digestion, good taste and good nutrition go together. But the cultural evolutionary perspective suggests a sketch of a stronger explanatory hypothesis. Random variation in food preparation procedures assures that somewhere, sometime somebody is going to do something that effectively prepares maize seed by exposing it to an alkali solution. Environmental selection assures that, over the long haul (possibly many generations), folks who consume maize prepared in this way will feel better, work and fight harder and smarter and thus have a better chance of producing more children than other folks who prepare their maize in other ways. Generational transmission assures us that cultural traits like food preparation technology will endure long enough so that environmental selection has time to do it’s thing.
