Question: How would I measure the concentration of sugar or apple juice in different brands of apple juice.
Answer: According to the wine doctor.com the refractometer is a device in which the juice from a wine grape is squeezed into and then provides a sugar reading of the juice content.
Another method, according to the wine doctor, is to use a hydrometer. The hydrometer is placed in the juice. The denser the juice, the higher the hydrometer floats; on the side of the stem is a scale, which allows the you to do a reading.