If you’ve ever eaten corn tortillas you will know that they behave and taste very different than flour tortillas. The texture is different, it breaks rather than tears but also their shelf life is shorter and the have a very characteristic taste.

If you’ve made your own flour and corn tortillas you will have seen that corn tortilla dough behaves very different. It doesn’t become as smooth a dough and during baking it doesn’t tend to puff up as much as for instance a chapati would.

Corn tortillas really are their own unique flatbread, with its own instructions to make (and store & eat) them. We’ll look into why that is and how the corn ingredient: masa harina, came to be.

Improving corn for nutrition & processing

Corn has been an important staple food for centuries in Southern America, where it originally comes from. However, corn, as opposed to most other staple grains, is very low in niacin, vitamin B3. If people would rely on corn as their main source of energy, they are at risk of developing pellagra. Pellagra is caused by a deficiency of vitamin B3.

Since the people in Southern America depended on corn though, they developed a way to overcome this ‘defect’ of corn. Corn does contain niacin, it just isn’t accessible for the human body. By soaking and then cooking the corn in an alkaline solution (alkaline is the opposite of acidic) the niacin does become available for adsorption by the human body. Processing helps them to get this important nutrient available.

This process is used to make masa harina, the basis for most homemade corn tortillas nowadays. After alkalization the corn is ground and dried. This gives masa harina.

Nixtamalization

The alkalization process of corn is called nixtamalization and doesn’t just improve the nutritional properties of the corn. It also improves the characteristics of the dough that is made from it for corn tortillas. So what really happens during the alkalization process?

As you know, corn contains quite a strong hull. This hull is even stronger for popcorn varieties. However, you can probably imagine this isn’t beneficial when you’re trying to make a soft dough. One of the main molecules in the corn hull is hemicellulose. Hemicelloluse is a large carbohydrate and happens to dissolve quite well in an alkaline solution. So, when the corn cooks in the alkaline solution, various molecules in the hull, not just hemicellulose, dissolve in the solution and will not be part of the masa harina.

Masa Harina vs Cornmeal

Corn tortillas can be made with as little as two ingredients: masa harina & water. Masa harina, as we just discussed, is alkalized corn, made into a flour. Even though it may look very similar to cornmeal, it definitely isn’t the same and you cannot substitute one for the other. Cornmeal hasn’t been alkalized, instead, it really is just milled corn. Because of that, the behaviour of cornmeal is slightly different than that of masa harina.

Making corn vs flour tortillas

Corn tortillas really aren’t that complicated to make, have a look at the recipe at the end of this post. It basically consists of mixing water & the masa harina, kneading it into a dough and pressing it into tortillas. If you are used to making flour flatbreads (e.g. pita) though, you will see that a corn tortilla behaves very differently!

First of all, a wheat flour dough is a lot more flexible. You can stretch the dough and if you need if for long enough it will become softer. Also, when you’re rolling out the dough you will be able to stretch it and shape it. That is not the case for a corn tortilla though. A corn tortilla dough is a lot more crumbly and so is the tortilla that you roll or press (hence the use of a press instead of a rolling pin!). This is all due to a lack of gluten in the masa harina. It’s the gluten that make the wheat flour stretchy and flexible.

From personal experience, it seems as if masa harina requires more time to hydrate than wheat flour does. However, it does not seem that there is any more substantial proof of this to be found.

The transformation of starch in tortillas

Once you have made the corn dough and rolled/pressed them into tortillas, you’ll bake the tortillas. You can bake them on any flat cooking surface on your stovetop. During cooking your raw dough will ‘cook’. During this cooking process a lot of things change in a corn tortilla. The main one is that transformation of starch, just like in potatoes, or a flour flatbread like pita.

Starch is a complex large carbohydrate, a specific group of molecules. Starch is made up of mostly amylose and amylopectin. Corn contains quite a lot of starch and you might have well used corn starch to thicken fruit fillings or sauces before. Raw starch is present in granules, the shape and properties of these granules differ per source of starch. Potato starch is different than corn starch which is again different than wheat starch. Also, the ratio of amylose:amylopectin content depends on its source. Even between different corn varieties these ratios can be very different.

Masa harina is quite unique though in its starch. Since it has already been cooked and treated with an alkaline solution, some of the starch has already changed during the process. The main change that occurs is gelatinization of starch. During gelatinization the starch absorbs water and ultimately the granules burst, releasing the starch into the liquid.

Researchers have actually looked into the changes that occur during processing of corn into tortillas, using a form of microscopy. On the photo below you can see the transformation of structures (further reading & source: Gomez, 1992).

Storage

Once the tortilla has been made and is taken off the stove, the quality will start going down almost immediately. The starch that was gelatinized during cooking will start to restructure itself in a process called retrogradation and the tortillas will start losing moisture. There are the main processes that also contribute to staling of bread.

In my personal experience, corn tortillas tend to go stale a lot faster and more intense than flour tortillas do. Part of the explanation (for commercial made ones) is that flour tortillas tend to contain some additional ingredients to help preserve their softness. For homemade ones though, there doesn’t seem to be a very clear explanation on this phenomenon and on whether it even is true!

The good news is though, that in a lot of cases, the retrogradation can (at least partially) be undone by re-heating a bread or tortilla in this case. The best way to store home made corn tortillas (or left over commercial ones) is wrapped up in a moisture proof barrier or a closed container, to prevent moisture loss, at room temperature. In the fridge retrogradation will occur a lot more rapidly. but if you want to store them for more than a couple of days storage in the fridge is your best bet since growth of moulds will be your issue, not so much the staling!

Don’t worry if you don’t have a tortilla press! Use two sheets of parchment papers, or, as we did have, two silicone baking mats. Put the dough in between and roll out using a rolling pin. Getting a perfect circle is a bit more of a challenge, but it still tastes great!

Corn tortilla recipe

This is a basic corn tortilla recipe, depending on the type of masa harina you’re using, you might want to slightly adjust the moisture content.

Also, if you’re interested in learning more about Mexican culture and food, you might want to watch the first episode of volume 5 of Netflix’ Chef’s table which interviews a Mexican, undocumented chef in the US.

Making corn tortilles - Masa harina science Yield: 8 tortillas Prep Time: 10 minutes Cook Time: 20 minutes Total Time: 30 minutes Print Ingredients 200g masa harina (not cornmeal)

240g water

salt to taste (you can do it without, depends on what you're used to) Instructions Mix the masa harina with the water. You might want to leave a little water behind so you can correct as you go. Knead the water in well, you will notice that the masa absorbs a lot of water even though it might look very moist at first. Knead the dough into a firm ball. The dough won't be as flexible and coherent as a flour tortilla dough due to the lack of gluten. Either use a tortilla press, or do what we did, roll the tortillas out using a rolling pin. Split the dough in 6 equal portions and shape them into nice round balls. Place some parchment paper (or a silicone baking mat or plastic bag) on the counter, place the dough on top and cover with another layer of parchment paper (or silicone baking mat or plastic bag). Use a rolling pin to evenly roll out the dough. Have a preheated flat pan on the stove on medium/high heat and cook on both sides until it's a light brown colour and cooked through.

Sources

Harold McGee, On Food and Cooking, 2004, p. 478-484

María Campechano Carrera, Elsa & Figueroa, Juan & Arámbula-Villa, Geronimo & Martinez-Flores, Hector & Jiménez-Sandoval, Sergio & Luna-Barcenas, Gabriel. (2012). New ecological nixtamalisation process for tortilla production and its impact on the chemical properties of whole corn flour and wastewater effluents. International Journal of Food Science & Technology. 47. 564-571. 10.1111/j.1365-2621.2011.02878.x., link

Itziar Egüés, Cristina Sanchez, Iñaki Mondragon, Jalel Labidi, Effect of alkaline and autohydrolysis processes on the purity of obtained hemicelluloses from corn stalks, Bioresource Technology, Volume 103, Issue 1, 2012, Pages 239-248, ISSN 0960-8524, https://doi.org/10.1016/j.biortech.2011.09.139.

Gomez, M.H., Corn starch changes during tortilla and tortilla chip processing, 1992, Cereal chem, 69(3):275-279, link, used image in accordance with copyright notice as mentioned in the article itself