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Making corn tortillas – Masa harina science
If you’ve made both flour-based flatbreads, such as chapati or tortillas, as well as corn-based corn tortillas. You’ll have noticed that the two doughs behave very differently. The corn-based tortilla isn’t as stretchy and can’t be rolled out as easily.
Corn tortillas are also very different from cornbread, especially the noticeably different flavor profile.
Both the characteristic behavior and the flavor of a corn tortilla are due to a unique way of treating corn: nixtamalization. Nixtamalized corn makes masa harina, which again makes the unique corn-based flatbread.
Improving corn for nutrition & processing
Corn has been an important staple food in the Americas for centuries. Over time people have developed a wide variety of ways to make it a nutritious source of food.
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.
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).
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!
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.
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
Luis Carlos Platt-Lucero, Benjamín Ramírez-Wong, Patricia Isabel Torres-Chávez and Ignacio Morales-Rosas, Viscoelastic and Textural Characteristics of Masa and Tortilla from Extruded Corn Flours with Xanthan Gum, 2012, Chapter 11, http://dx.doi.org/10.5772/49975, link, great read on scientific work done on improving commercial manufacturing of corn tortillas
Wang, S. , Li, C. , Copeland, L. , Niu, Q. and Wang, S. (2015), Starch Retrogradation: A Comprehensive Review. COMPREHENSIVE REVIEWS IN FOOD SCIENCE AND FOOD SAFETY, 14: 568-585. doi:10.1111/1541-4337.12143, link ; great read if you want to learn more about starch retrogradation
Ratnayake, Wajira S. and Jackson, David S., “Gelatinization and Solubility of Corn Starch during Heating in Excess Water: New Insights” (2006).
Faculty Publications in Food Science and Technology. Paper 118. http://digitalcommons.unl.edu/foodsciefacpub/118, link; good article to learn more about gelatinization
R.J. Weber, Shelf life extension of corn tortillas, 2000, MSc thesis for Kansas State University, link; article on the shelf life extension of corn tortillas
Nice article, but I think the recipe needs a correction – hard to get 8 tortillas from 6 balls of masa…
Hi Mike, great catch, thank you! Just made the correction.
Excellent article! Your recipe is missing a few key points. First, the water must be at least 162°F to maximize gelatinization. Hotter is better since it will cool down as it mixes with the room temperature harina. It must be given time (~15 minutes) to hydrate. These conditions will cause the tortilla to trap steam while cooking, meaning bubbles form. Bubbly tortillas are more pliable and have a better mouth feel. The rough edges of your tortillas indicate to me that they were under hydrated.
Thank you for the science!
Those are some great additional tips! Thank you, we’ll incorporate those into the article 🙂