1. A device for determining sugar content of an agricultural product while being harvested, comprising: a sample preparation mechanism for attachment to a harvester/defoliator and for use with a received agricultural product during harvesting to create an exposed sample of the agricultural product; an illumination chamber for radiating the exposed sample of the agricultural product; a sensor head for receiving radiation from the exposed sample of the agricultural product; a spectrometer, coupled to the sensor, for converting the radiation into a corresponding spectral signal; and a computer, coupled to the spectrometer, for receiving the spectral signal and for processing the spectral signal to determine an indication of sugar content of the agricultural product.