Choose ginger with the smoothest skin. Fresh ginger is hard and breaks cleanly with a snap. If there are wiry protruding fibers at the break, you have old ginger and if the skin is wrinkled your piece of ginger is old.
The fresher the ginger the better. When it is fresh its juicy, hot and sweet with no bitterness. Fibrous older ginger can be used in braised dishes and in broths.
Ginger if kept in the refrigerator should be wrapped in a paper towel or in a plastic bag that is kept open and will last up to a month.