Peritectic reactions can cause surface defects and breakouts in continuous casting and the peritectic region is often avoided by adjusting the chemical composition of the steel to cast outside of the peritectic sensitivity range. However, the combined effects of C, Mn, Al, and Si on the boundaries that map peritectic region are still disputed for many advanced high strength steel grades. An apparatus for performing controlled solidification experiments is being developed to characterize the effects of chemical composition on the uniformity of shell growth during solidification using a copper chill mold with an embedded fiber-optic temperature sensor that enables high spatial resolution temperature mapping. The spatially distributed fiber-optic sensor employs optical frequency domain reflectometry to measure temperatures with a 0.6mm spatial resolution along the length of the fiber at a 20ms sampling rate to map closely spaced temperature features caused by the peritectic reaction. This paper reports progress on the ongoing efforts to develop a peritectic sensing system using optical fiber temperature sensing technology.