Molasses is a tasty by-product extracted during the process of refining sugar cane into sugar crystals. Treacle is blend of refinery syrup and molasses that ranges in color from light gold to nearly black.
In the United Kingdom and Europe, molasses is often called black treacle. Originally, treacle was a pale, refined type of molasses that was notably sweeter and had a more mellow flavor than most molasses. Treacle can be substituted for molasses in most recipes, but molasses usually doesn't work as a substitute for treacle, unless it is a very light and unsulphured molasses. Other varieties of molasses include blackstrap, light, medium, dark and sorghum molasses.