The Mishnah describes the preparations that preceded the time of biur: the beis din would send messengers out to the farmers living in the outlying areas, in the country towns, and call out to them to hurry and complete their obligations before the time of biur arrived.
"Maharu v'sak'nu es peiroseichem":
This was the wording of the proclamation, and setting the produce in order includes two things:
Separating Terumah and ma'asros - completing all the separations required from the produce.
Bringing the ma'aser up to Jerusalem - making sure that a person brought what was his to Jerusalem and did everything incumbent upon him before the time of biur arrived.
The urgency stems from the fact that once the time of biur has arrived, a person can no longer recite the confession of the ma'aser properly, since the confession is based on his having fulfilled the mitzvos as required.
Rabbi Akiva's novel teaching:
This is how they would proclaim, until Rabbi Akiva came and taught: produce that has not reached that stage of processing called "onas hama'asros" - the stage at which it actually becomes liable for separation, with the smoothing of the pile - is not included in the obligation of biur. The obligation of biur applies only to what has reached that point.
Consequently, anything that has not reached that stage does not prevent a person from reciting the confession of the ma'aser and testifying about himself that he did everything properly. The laws of biur do not apply to it: neither to destroy it nor to dispose of it, and not even to make sure that the Terumah and ma'asros were given to the people entitled to them. That entire obligation does not take effect until the produce has reached "onas hama'asros."
In summary: we learned that the beis din would urge the farmers on with the call "Maharu v'sak'nu es peiroseichem" - to separate Terumah and ma'asros and to bring the ma'aser up to Jerusalem - before the time of biur, since afterward the confession can no longer be recited properly. And Rabbi Akiva taught that any produce that has not reached "onas hama'asros" is not subject to biur and does not prevent the confession of the ma'aser.