Romaine lettuce's high water content means there is no long-term preservation method suitable for making the lettuce last longer. Drying, canning and freezing all produce inedible results. For the best nutritional value, romaine lettuce is best served when it's fresh, green and crisp. Storing the lettuce in a refrigerator is the best option for preserving it, although there are a few other measures that can be taken to ensure romaine lettuce lasts as long as possible.
Fill a clean sink half way with cool water.
Cut off the core of the lettuce with a clean, sharp knife.
Separate the romaine lettuce leaves and submerge them in the water.
Swish the lettuce leaves around in the water until all of the dirt or other residue is removed from the leaves.
Dry the romaine leaves by spinning them in a salad spinner or dry each leaf thoroughly with a clean dish towel.
Line the crisper drawer in the refrigerator with dry, clean kitchen towels or paper towels to absorb excess moisture from the leaves.
Layer the leaves on top of each other in the drawer on top of the towels.