E-juice lasts longest and tastes best when it is kept in a cool, dark, tightly sealed bottle at roughly 60 to 70°F, away from sunlight, heat, and open air. Stored this way, most e-liquid stays fresh for one to two years. Steeping, which means letting a sealed bottle rest in those same conditions for one to two weeks with an occasional shake, can deepen rich flavors like desserts, custards,...