Celery should be fresh, crisp, clean, of desirable length, thickness, and solidity, with good heart formation and branches that are brittle enough to snap easily.  Pithy, woody, or stringy celery is undesirable.  Soft somewhat pliable branches indicate pithiness and small hard branches may be woody and stringy.

Grades    U.S. Extra No.1, U.S. No.1, and U.S.No.2.  There are also U.S. Consumer Standards for Celery Stalks. for use in retail.

U.S. Extra No.1 well formed, clean, well trimmed, compact and free from black-heart, brown stem, soft rot, doubles and free from damage caused by freezing, growth cracks, pithy branches, wilting, suckers, blight insects, and mechanical damage. Stalks shall be green unless otherwise specified.  The average midrib length of outer whorl of branches shall not be less than 7 inches.  When stalk length is specified, it shall be the minimum length in terms of whole inches in even number, as 12 inches, 14 inches etc. in accordance with the facts.