The OU dispatches a rabbi to check out a company that has applied for certification. The OU tries to use one of its rabbis to do an initial inspection at the company's facility which is really a feasibility study to determine how the OU can create a Kosher program at the company's facility. Once that program is established, a contract is signed whereby the company is now obligated to follow the Kosher standards. A rabbi visits the plant on a periodic, unannounced basis to make sure that the company is maintaining Kosher standards. This unannounced visit can happen anywhere from twice a year to everyday.
Some plants have full time rabbinical staff.
Kosher meat is much more complicated Kosher meat on the other hand, is much more complex and the standards are stricter. Fish also gain a Kosher designation. All Kosher fish have fins and scales. The animal has to be slaughtered in a prescribed manner by a rabbi who is trained in that craft . He is called a Shochet or the ritual slaughterer.