Fermentum

Fermentum is a practice of the Early Christian Church whereby bishops affirmed their communion with one another.

The custom of the fermentum was first practiced as early as 120 AD. A particle of the Eucharistic bread was carried by a minister of the Church from the bishop of one diocese to the bishop of another diocese. The receiving bishop would then consume the species at his next celebration of the Eucharist as a sign of the communion between the churches. The term fermentum was probably a reference to the Eucharist as the leaven of the Christian life, and as the instrument by which Christians spread throughout the world were united in the one Body of Christ as a leaven to the world.