The belief that searing meat "seals in the juices" is widespread and still often repeated. This theory was first put forth forward by Justus von Liebig, a German chemist and food scientist, around 1850[1]. The notion was embraced by contemporary cooks and authors including Auguste Escoffier.
Simple experimentation can test the theory: cook two similar cuts of meat, searing one first and not the other. Weigh the end results to see which loses more ...