What instrument is required to measure the maturity of table grapes?

The refractometer is the appropriate instrument for measuring the maturity of table grapes because it assesses the sugar content in the juice of the grapes. As grapes mature, the sugars increase, which is a crucial indicator of ripeness and quality. The refractometer helps vintners and growers determine the ideal harvest time by providing a precise reading of the fruit's sugar levels, typically measured in Brix. This information is vital for ensuring that the grapes have reached the desired flavor profile and sweetness prior to harvest, making it an essential tool in grape cultivation and wine production.

Other instruments mentioned, such as a hydrometer, are primarily used for measuring the specific gravity of liquids and wouldn't provide the same level of detail related to grape maturity. A pH meter measures acidity, which, while useful, does not directly indicate sugar content and thus maturity. A caliper measures physical dimensions and would not be relevant in evaluating the chemical qualities that determine ripeness.