Gleaning is going over a field or area that has just been harvested and gathering by hand any usable parts of the crop that remain.

There are several Biblical references for gleaning.

Leviticus 19:9-10

When you reap the harvest of your land, do not reap to the very edges of your field or gather the gleanings of your harvest.  Do not go over your vineyard a second time or pick up the grapes that have fallen.  Leave them for the poor and the alien.  I am the Lord your God.  (NIV)

Deuteronomy 24: 19-21

When you are harvesting in your field and you overlook a sheaf, do not go back to get it.  Leave it for the alien, the fatherless and the widow, so that the Lord your God may bless you in all the work of your hands.  When you beat the olives from your trees, do not go over the branches a second time.  Leave what remains for the alien, the fatherless and the widow.  When you harvest the grapes in your vineyard, do not go over the vines again.  Leave what remains for the alien, the fatherless and the widow. (NIV)

A number of our produce contributors actually give their "first fruits" – that is, they allot a portion of their crop prior to the harvest.  They feel that God has so abundantly blessed them that they want to "give back" to the community.