Let’s Talk Masa

Masa is a unique corn dough that’s the basis for both tamales and tortillas. More than just a simple combination of ground corn and water, it’s actually made from corn that’s been nixtamalized. That’s quite a mouthful of a word, and it refers to corn that’s been treated with a weak alkaline solution. It comes from the Aztec word “nixtamal” which, loosely translated, means “ash dough.”

Not very appetizing by the sound of it. However what ancient Mesoamericans discovered 3,500 years ago is that when you boil and then soak raw corn kernels together with ashes, some very interesting things happen. Most noticeably, the outer hulls (pericarps) of the kernels loosen to the point that they can be slipped off.

So nixtamalization is all about heat and water then? Er, not quite. The key component is really the ash, which, long-time readers of joepastry.com may remember, has a high pH. Add a handful to a pot of water and you get an alkaline solution that goes to work dissolving the glues that hold the walls of the pericarp cells together (the hemicellulose and pectins). The pericarp loosens and falls off, and the endosperm swells as it takes in more and more of the chemical-laden water. As it does, the tight bundles of starch molecules in the endosperm start to come apart and the corn becomes soft and pliable. What you get, once the corn is finally drained and washed, is a processed corn product that’s easily ground into a smooth and elastic dough.

Neat. But it all begs the question: how did the ancient Mesoamericans hit on this process? Unknown. It may have started when someone mixed a few wood ashes in with some corn gruel (a common technique that indigenous American peoples used to lighten — really leaven — cakes made from grains). But who knows? Wood ashes (which contain potassium carbonate) weren’t the only alkaline compounds available to the peoples of that time. Naturally occurring lime (calcium carbonate-rich limestone and/or chalk deposits) were also used, as were the ashes of burned mussel shells.

These days, most people who make corn masa from scratch dispense with the burned shells and simply use a commercially-made product that goes by the name of “cal” in Mexico. Calcium hydroxide is what it is, commonly known as “slaked” (dissolvable) lime in America. It can be found in most Mexican markets in the spice section.

Buying the cal and boiling and steeping the corn is the easy part, however. The real challenge when it comes to making one’s own corn masa is the grinding. Getting it fine enough to make tortillas is no easy task. Food processors aren’t good enough. What’s needed is either a plate grinder or a good, old-fashioned metate. I’ve never used one, but I can imagine they call for more elbow grease than I’d be willing to put in for home-made tortillas. But those of you who might be interested, knock yourselves out! You can get them in Mexican markets as well. They cost less than you’d think.

2 thoughts on “Let’s Talk Masa”

  1. I love this blog because I get to see all the chemistry I learned come to life. 🙂 The process you describe of dissolving the pericarp is called an acetal hydrolysis. See, I study for the MCAT even when reading your blog! What I can’t figure out, though, is how the wood ash incorporates gas into corn gruel to leaven it. I feel like this could be seen as a cooking/baking trivia, but for a person trying to learn how to create her own recipes, knowing the chemistry can be really helpful! any insight?

    1. Ah yes, that would be because in the past the corn gruel would have sat out a fair bit and fermented. That’s where the acid would have come from for the leavening reaction: bacteria. Potassium carbonate + lactic acid = gas (and some other stuff).

      – Joe

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