Lye water and dried tangerine peel can both be found Asian markets and online. We recommend whole pieces of dried tangerine peel because they’re more flavorful than precut peels. Removing the white pith from the peel after soaking reduces bitterness. To freeze the beef balls, cook and cool them and transfer them with the tofu skins to a plate or baking sheet lined with parchment leaving space between each. Freeze until solid, at least 4 hours. Transfer to a freezer bag and freeze for up to 1 month. To reheat, steam frozen beef balls in a steamer basket on a heatproof plate until soft and heated through, about 12 minutes.