Think back to your chemistry days where you had different tools to measure chemical content of liquids….or is that only me with my Chemical Eng background? Anyway, there is a very simple tool called a Refractometer that will measure the sugar content of the grapes.
In the picture above you can see that you simply squeeze the grape and put the liquid on the glass window and cover it with the lid. Then you look into it like a kalaidascope and a line will appear on a scale and you will know the content. Hard to explain on paper, but easy to do.
In the vineyard you now have to measure a good number of samples every week until you get to the desired sugar level. I’m shooting for 23.5% that will give me a wine with a little under 14% alcohol.
In addition, for the flavors you can tell if the grapes are ripe by the color of the seed. If the seed is green it isn’t ready. If it is brown…..good to go.