Syneresis is an integral part of cheese manufacture. The rate and extent of syneresis affect the properties of cheese. There are many factors that affect syneresis, but measured results vary because of inaccuracies in measuring techniques. To better control syneresis, an accurate mathematical description must be developed. Current mathematical models describing syneresis are limited because of inherent error in measuring techniques used to develop them. Developing an accurate model requires an accurate way to measure syneresis. The curd becomes a particle in a whey suspension when the coagulum is cut. The most effective technique to measure particle size, without interference, is with light. Approximations to rigorous Maxwellian theory render useable results for a variety of particle sizes. Assumptions of Fraunhofer diffraction theory relate absorption to the cross sectional area of a particle that is much larger than the wavelength of light being used. By applying diffraction theory to the curd-whey system, this researcher designed a new apparatus to permit measurement of large particle systems. The apparatus was tested, and calibrated, with polyacrylic beads. Then the syneresis of curd was measured with this appaatus. The apparatus was designed to measure particles in suspension. Until some syneresis takes place, curd does not satisfy this condition. Theoretical assumptions require a monolayer of scattering centers. The sample container must be thin enough to preclude stacking of the particles. This presents a unique problem with curd. If the coagulum is cut in the sample cell, it adheres to the front and back surfaces and does not synerese. The curd must be coagulated and cut externally and transferred to the sample cell with a large amount of whey. This measurement technique has other limitations that may be overcome with commercially available accessories.