On the feast of the Transfiguration the Church blesses the first-fruits of the harvest both as a giving back to the Lord what is His and has come from Him (1 Chronicles 29:14) and as a celebration of the promise of the final transfiguration of all things in Christ. The Divine Light glimpsed by the Apostles on Mount Tabor will transform all creation to its most perfect flowering and fruitfulness.
In Constantinople and the Greek world grapes were placed on a table in the center of the temple and offered and blessed at the end of the Divine Liturgy and then partaken of by the faithful. Over time this blessing was extended as other first-fruits were brought to be offered and blessed. The Trebnyk (Euchologion or Book of Needs) offers several different prayers, one of which is offered here:
Prayer for the Blessing of First-Fruits
O Lord God Jesus Christ, You said to Your disciples: "Whatever you ask in prayer, believe that you have received it, and it will be yours." We now humbly beseech You, bless + and sanctify these first-fruits which Your faithful servants have brought into Your temple today. Preserve the life and health of all those who partake of them, those who are present here and those who absent. Grant that these blessed first-fruits be an effective medicine for those who are sick and ailing, and a protection against the assaults of the enemy for those who keep them in their homes. May all those who partake of them enjoy the fullness of Your goodness and blessing. For You, O Christ God, are our true nourishment and the Giver of all that is good, and we send up glory to You, together with Your Father, Who is without beginning, and with Your all-holy, good, and live-giving Spirit, now and ever, and to the ages of ages. Amen.