I saw a technique that I knew about but had never seen in action on grapes while I was in a table grape vineyard in Fresno — girdling.  Girdling is technically the removal of a complete ring of outer and inner bark, extending in depth to the cambium, usually on a trunk and resulting in a temporary interruption of the downward translocation of metabolites in the phloem.  This action results in the metabolites being used in the upper portion of the vine leading to higher sugar levels in the grapes.

A vine that has been girdled with 3 circling cuts. The damage will eventually heal over.

Sugar and size are big concerns for table grape production and this technique helps with that.  Other fruit crops are girdled too depending on the desires of the grower (and the resulting market).