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Use the entire stalk, which will be cut and prepped in different ways depending on the dish. The tough, bigger pieces of lemon grass are meant to flavor dishes. These larger pieces generally are not eaten. Consider straining large pieces out before serving. However, some people enjoy sucking on them for their flavor.   Store it in a plastic bag that's securely sealed. You can freeze lemon grass for as long as 6 months.

Summary:
Keep pieces small for eating and larger for flavoring. Discard the dry, outermost stalks and cut off the top third of the inner stalks. Trim each root tip until the purple rings are visible. Keep fresh lemon grass in the refrigerator for up to 3 weeks.