A refractometer is an optical instrument used to measure the refractive index of liquids. It works by shining light through a sample and measuring how much the light bends, which can indicate the concentration of dissolved substances, such as sugars or salts. This tool is commonly used in various fields, including food and beverage production, laboratories, and agriculture. There are different types of refractometers, including handheld models and digital versions. They are essential for quality control in industries like winemaking and brewing, where precise measurements of sugar content are crucial for fermentation processes.