Legally specifying the locality of a ham's ultimate curing process ensures a uniformity in flavor, since the curing environment's air quality, humidity, and local varieties of airborne mold spores (whose enzymes are produced as a byproduct of growth on the ham's rind) produce both a unique and systematically replicable flavor.
Genuine Smithfield hams [are those] cut from the carcasses of peanut-fed hogs, raised in the peanut-belt of the Commonwealth of Virginia or the State of North Carolina, and which are cured, treated, smoked, and processed in the town of Smithfield, in the Commonwealth of Virginia.
The "peanut fed" and "peanut belt" stipulations were removed in 1966. The present statute reads:
...Genuine Smithfield hams are hereby defined to be hams processed, treated, smoked, aged, cured by the long-cure, dry salt method of cure; and, aged for a minimum period of six months; such six-month period to commence when the green pork cut is first introduced to dry salt, all such salting, processing, treating, smoking, curing, and aging to be done within the corporate limits of the town of Smithfield, Virginia
While unclear whether hams may be come from pigs raised and slaughtered elsewhere, this stipulates only that a six-month curing clock begins whenever cuts of pork are "introduced to dry salt", and that the duration of processing must occur within Smithfield.