Heating white corn tortilla shells, usually called tortillas, takes them from dry and crumbly to moist and pliable. Hard cooked shells require minimal heating, but unheated tortillas are barely edible and not pliable straight from the bag. Heat them properly and they become more appetizing and ready for filling with a variety of ingredients. There's no difference between heating yellow or white corn tortillas, except if you have a preference in the slight difference in taste -- color is all that defines white or yellow corn tortillas. There's more than one method you can use to heat the tortillas. But with whatever method you choose, the key is keeping them moist and heating them for a short period to avoid drying them out.
Steam
Fill the bottom of the steamer with water until it comes up to 1/2 inch on the sides.
Line the steamer basket with a clean, thick kitchen towel.
Stack the tortilla shells in the towel.
Wrap the towel around the tortillas to cover them.
Set the lid on the steamer.
Place the steamer on a stovetop burner set to medium-high heat.
Bring the water to a boil for 1 minute.
Turn off the burner and let the tortillas stand in the covered steamer for 15 minutes.
Skillet
Place enough oil into the skillet just to coat the bottom of it.
Set the skillet on a stovetop burner set to medium heat.
Place one tortilla at a time in the skillet.
Cook the tortilla on one side for about 1 minute.
Flip the tortilla to the opposite side with a pair of tongs or a spatula and cook for 1 more minute, or until the tortilla is soft and warm.
Microwave
Lightly moisten a kitchen towel with water. Wring it out to remove any excess water. It should feel barely damp.
Line a microwave-safe dish with the towel.
Stack the tortillas on top of the towel and fold the towel over to cover the tortillas.
Heat the tortillas in the microwave at 50 percent power for 4 minutes.