Definition - What does Cap Stem mean?
The cap stem is the part of a grapevine which forms in the spring from which the grape flower clusters are born. The main axis of the cluster is called the rachis. Each individual flower is contained by the cap stem (also called a pedicel) that is attached to the rachis.
WineFrog explains Cap Stem
Within the cap stem are the five stamens; the male, the female pistil, the ovary, the style and the odor glands. These are the organs which are necessary for fruit development and later develop the flower cap (calyptra), made up of five fused petals that protect the flower organs within the cap stem before the petals open or bloom in the spring.
The moment when the bloom occurs is called anthesis and usually happens six to eight weeks after shoot growth.