Tortillas

Store-bought flour tortillas keep about a week at room temperature or 3–4 weeks refrigerated, and about 6–8 months frozen. Corn tortillas keep a similar time and stale faster.

Keep them sealed. Tortillas are thin and dry out quickly, going stiff and cracking at the fold — the resealable bag they came in works well, or an airtight container.

Freezing is the best option for anything beyond a week or two. Separate the tortillas with parchment or wax paper before freezing so you can take a few at a time, since a frozen stack is very difficult to prise apart.

Reheat directly on a dry skillet or a gas flame for a few seconds per side. The microwave makes them gummy; a dry pan restores them properly.

Fresh tortillas from a tortilleria have no preservatives and keep only a few days.

Tortillas are flatbreads, and they fail in the same two ways as any bread: staling and mold.

Staling is starch retrogradation — starch molecules recrystallizing and expelling water, making the tortilla stiff and prone to cracking. As with a loaf of bread, this runs fastest at refrigerator temperatures and effectively stops in the freezer, and it is partly reversed by heat. That is why a stale tortilla comes back to life on a hot dry pan and why the freezer is the better storage choice.

Mold is the other failure, and it is why commercial tortillas contain preservatives such as calcium propionate and, in many cases, an acidulant to lower the pH. Those are the reason a supermarket tortilla lasts weeks while a fresh one from a tortilleria lasts days.

Corn and flour tortillas differ meaningfully. Corn tortillas are made from nixtamalized corn — treated with an alkaline solution, which improves nutrition and flavor — and contain no fat, so they stale faster and more brittlely. Flour tortillas contain fat, which interferes with starch recrystallization and keeps them pliable longer.

Discard the whole package on any mold, as with bread — the filaments run through the stack invisibly. Stiffness and cracking alone are staling and are fixable with heat.