A sensor for measuring diffuse reflectance of milk during the typical 6-h culture of cottage cheese was installed in a local manufacturing facility. Diffuse reflectance was found to increase slowly during the first three hours of the culture and increase rapidly toward the end of fermentation. The correlation between parameters generated from the diffuse reflectance profile and cutting time was sufficient to develop an algorithm for cutting time prediction. An algorithm incorporating tmax (time from adding culture to the maximum rate of change in reflectance) and slope of the reflectance curve at tmax predicted the operator selected cutting time with a standard error of 8.7 min.