After the search in the evening, one should immediately annul the chametz, with the formulation "All leavened produce... that I have not seen... may it be annulled and insignificant like the dust of the earth." The first word [when recited in Aramaic, hamira] is a general word for chametz (leavened food) and se'or (leavening agent). One should also understand that this nullification makes the food ownerless, and it is no longer legally in one's possession. One should recite this nullification formula three times, as is written in the work "Machzik Beracha".