In the continuous casting process infiltration of the liquid slag into the gap between the strand and the mold is a key parameter to guarantee process stability as well as product quality. Also the temperature-dependent solidification behavior of the slag influencing the horizontal heat transfer from the strand to the mold plays an essential role. Thus, to characterize mold slags the break temperature (TBr), which is related to the formation of the first crystals in the slag, has become a characteristic parameter. Methods to determine TBr and interpretation of the results will be shortly reviewed. In most cases TBr is determined from viscosity measurements. Nevertheless, also capacity measurements have been employed recently. In this presentation a new automated procedure to evaluate TBr from viscosity ɳ in dependence of temperature T will be shown. Viscosity is measured in dependence on temperature for a defined cooling rate. According to state of the art, TBr is determined manually via tangent method applied to the log ɳ versus 1/T representation. This is more time consuming than an automated method, and may be less impartial. For the automated procedure the maximum of the second derivative of log ɳ with respect to 1/T is calculated and the associated temperature is related to the break temperature. Due to fluctuations between data points previous regression is essential. Comparing the values of the calculated break temperature with those obtained by manual determination shows good agreement. The error was estimated by statistical analysis. Additionally, the effect of sampling frequency was investigated.