Rijk's - When are grapes ready for harvest?

Figuring out when to harvest our grapes is one of the most important decisions Pierre, our winemaker has to make every year. Months and months of tending the vines, spraying, making sure soils are healthy, determining watering regimes, etc. culminates in the crucial decision of choosing precisely the right time to harvest those juicy grapes. Of course perfect ripeness is what winemakers look for, but what defines ripeness? Can you tell by how the grapes look or taste? Is there some kind of measurement that can be taken objectively? The answer is that it's both of these things.