In cheese manufacture milk proteins called casein micelles are destabilized to form a gel, which is cut, resulting in syneresis i.e. the expulsion of whey from curd particles. Manufactures are concerned with controlling cheese yield which is dependent on two factors namely whey fat losses and curd moisture content. Monitoring whey fat changes during syneresis may provide valuable information which will assist in developing sensor technologies for controlling cheese yield. The objective of this study was to determine if light sidescatter measurements of whey may be used to determine whey fat content. A fully randomised two-factor (milk fat content, gel cutting firmness) three-level factorial experimental design was employed. Milk coagulation was carried out in an 11 I vat. The gel was cut at the firmness required using a rheometer running simultaneously with coagulation in the vat. During syneresis samples were removed from the vat, at 20 min intervals after cutting. A portion of each whey sample was analyzed for fat, while the remainder was placed in a specially designed temperature-controlled cell which allowed for the recording of sidescatter spectra (300-1100 nm) using a fiber optic spectrometer. Spectra were subjected to principal component analysis. The first two components (PC) explained 100% of the variance in the spectra, and showed that it was possible to discriminate between samples on the basis of milk fat content. A whey fat prediction model was developed using partial least squares regression. The model predicted whey fat content with a root mean square error of cross-validation of 0.047 g/100 ml over a range of 0.502 g/100 ml (R - 0.94) using two components. These results indicate that light sidescatter has potential to monitor whey fat content.