When we judge the ripeness of our grapes to decide if they are ready to be picked we look at two different kinds of ripeness.
One is the physical ripeness, simply meaning the sugar content which again translates into potential alcohol. This is measured using a refractometer that shows sugar density in the juice inside the berries.
However, this only tells us at what alcohol percentage the wine will end up with after fermentation,. Though Mother Nature often makes sure that it hits the optimal 12 to 14% alcohol at the exact same time as we reach perfect phenolic ripeness.
This refers to the ripeness of the skins and seeds and thus all the flavour compounds and tannins. This is something that can only really be measured by a human palate so we eat a LOT of grapes just before harvest.The last thing we want is a wine at 13% that tastes like nothing and with bitter, unripe tannins, so we put a lot of effort into choosing the optimal day of picking for the different kinds of ripeness to be optimal and aligned