Tortilla tricks: Best way to buy and store supermarket tacos shells and more

What's the real deal with corn versus flour tortillas? (Christopher Testani)

In Chicago,  more than a few tortillerias supply fresh tortillas to grocery stores big and small across the city. This does wonders for Taco Tuesday.

But if you can't find them fresh, there are plenty of supermarket options. Store-bought tortillas are a $12 billion industry, and if you haven't noticed, the supermarket is stacked with options, from mini "street taco" tortillas, to gluten-free, whole-grain, and low-carb ones (arguably toeing the line between tortilla and wrap, but that's another story), to everyone's childhood favorite, the hard-shell taco. A pumpkin spice tortilla can't be far behind.

The shelf-stable tortilla is a relatively recent phenomenon, says Stephen Jones, a wheat breeder and director of the Bread Lab at Washington State University. (The exception is the hard-shell taco, which dates to the late 1940s.) "Tortillas always used to be refrigerated," says Jones, who led development of a preservative-free tortilla for the Chipotle restaurant chain.

So how did we go from a four-ingredient tortilla to a 14-ingredient one? In a nutshell: food science. Here's how to make sense of all that the tortilla aisle has to offer.

Tortilla basics

You can count on one hand the number of ingredients in a traditional tortilla.

A flour tortilla contains flour, salt, water, oil, and, usually, a leavening agent. For a corn tortilla, it's corn, lime—as in calcium hydroxide—salt, and water. (oaking corn in this lime solution, a process called nixtamalization, makes the corn easier to grind into fresh masa and its nutrients more available and easier to digest. That said, most supermarket corn tortillas start not with masa but masa harina flour.

If your store stocks fresh, locally made tortillas like mine does, the ingredients on the package will read something like the above.

"Any deviation from that, in terms of what else is in there, is there to make the process more simple—that's probably truer for flour tortillas than corn—to make [the tortilla] last longer, and to make it more pliable," says Jones.

So what else is in a typical store-bought tortilla?

A lot! Guar gum and cellulose gum keep tortillas soft. Other additives such as fumaric acid, phosphoric acid, sorbic acid, and calcium propionate have dual roles as dough conditioners and preservatives, Jones says.

Depending on the brand and the style of tortilla—super soft seems to be the ideal quality tortilla-makers strive for—there might be sweeteners and other starches and stabilizers that help with texture and shelf life.

"It's tough to wrap something with a cold tortilla, so that's why a lot of that stuff is in there. They're incredibly pliable, which is not a natural state. That takes some chemistry," says Jones.

The best way to buy tortillas

Buy in quantities you know you're going to use and read the labels. Better-quality tortillas will have fewer ingredients, all of which you should be able to pronounce. Locally made ones are as fresh as you can get. They won't have been sitting for weeks, on a truck en route to the store and then on the shelf in the store, like typical industrial tortillas.

With flour tortillas, check if they're made with bleached or unbleached flour and go with unbleached if possible. Common bleaching agents include acetone peroxide and benzoyl peroxide—as in, acne-fighting benzoyl peroxide, says Jones.

What's the shelf life of tortillas?

A long time, if we're talking mass-market ones; a few days for freshly made.

The typical shelf life for a pack of flour or corn tortillas is anywhere from 16 to 45 days—a little longer for those sold in the refrigerated section—and up to six months for taco shells, according to Mission Foods, a leading brand whose parent company dominates the U.S. tortilla market.

Check the date on the package. Once you open it, the tortillas will keep until that date whether stored in your pantry or the fridge, according to Mission.

But do you really want to eat a three-month old tortilla? Better to think of tortillas as you do fresh produce, says Jones. Buy and use what you can right away, freeze what you don't use within a day or two—tortillas freeze well, in airtight packaging—and thaw them in the fridge. Taco Night will be here again before you know it.

More: How to Make Fresh Corn Tortillas at Home