Definition - What does Cluster Stem mean?
The cluster stem, or bunch stem, is the name for the stalk, which extends from a shoot where the fruit develops.
Shoots will appear in the spring and be followed by bud break. These buds will later become other shoots and canes or become fruit-producing buds where the bunch stem will develop.
WineFrog explains Cluster Stem
In the spring as grapevines begin to show new growth, they will develop small flowers. These flowers are only 4 to 5mm long and are found grouped together in a cluster, called inflorescence. Before they bloom, the calyptra, which is a cap of fused petals, encloses the flower's other parts. It then detaches itself from its base of the bloom and exposes pollen-bearing stamens and the pistil with the ovary.
This is the development of the cluster stem. The ovary of each flower will develop into a berry when it is pollinated. The stem, which grows from the main cane to hold the cluster stem is called a peduncle.