A refractometer is an invaluable tool for any size winegrower. A refractometer lets you know when to pick. And, they can do it by just picking a few drops of grape juice from all over the vineyard. Another method is to extract enough juice from the grapes to take a reading with a wine hydrometer. This can take as many as 200 berries crushed and pressed.
How a refractometer actually works is very interesting. They can tell you what percentage of sugar is in a drop of liquid, how much the sugar bends or refracts as it passes through. To see refraction in action, place a straw in a glass of water. The above water straw and the underwater straw look like they broke in two. That's refraction.
If you were to dissolve some syrup in a glass of water, the straws would seem to disconnect, and as you continued to dissolve more and more sugar, the "two straws" would get farther and farther apart. This is the premise that a refractometer can tell you how much sugar is in the grapes.
Place a drop of grape juice between the prism of the refractometer and the light-shielding plate. How much the light is bent as it passes through the prism and through the barrel of the refractometer tells you the percentage of sugar in the sample. When you look into the eyepiece, you will be able to observe the refraction relative to the scale.
Because of how a refractometer works - and how easy it is to do - anyone with a vineyard of any size will find it extremely useful. Only a few random samples are needed to get an accurate picture of how the grapes are growing
