Without preservatives, mochi is best eaten the day you make it. On the day of making, you can store it at room temperature. If you must store the mochi, it's best kept in an airtight container or tightly wrapped in the fridge or freezer. When the mochi has been chilled, it often firms up and loses its chewy texture. To salvage the mochi, warm it up in the microwave for a few seconds or steam it for a few minutes.