Selective harvesting, usually based on field sampling by taste, is an established practice in the wine industry, but its relationships to principles of viticulture and grapevine physiology are not well understood. To move toward greater understanding of those relationships, physiological data was collected over the 2007 and 2008 growing seasons in a premium-production Napa Valley vineyard block with a history of variable grape quality. Data vines remained as individual study units throughout data gathering and analysis and geographic information systems (GIS) were used to relate the vines spatially. Areas yielding grapes with perceived higher quality had vines with 1) lower leaf water potential (LWP) both pre-dawn and mid-day, 2) smaller berry diameter and weight, 3) lower pruning weights, and 4) higher soluble solids (°Brix). A trained sensory panel found that grapes from the more water-stressed vines had significantly sweeter and softer pulp, absence of vegetal character, and browner and crunchier seeds. Metabolomic analysis of the grape skins showed significant differences in accumulation of amino acids and organic acids. None of the results (physiological, sensory, chemical) showed a strong or consistent linear relationship with LWP, but were significant when grouped into vines experiencing mid-day water stress at veraison ≤-1.5MPa and >-1.5MPa, which correlate to the areas described as producing higher and lower quality fruit. These results suggest that there is not a linear relationship between physiological water stress and grape sensory characteristics, but rather the presence of an inflection point controlling grape composition as well as physiological development.