Sulfur dioxide
Many kinds of molasses on the market come branded as "unsulfured". Many foods, including molasses, were once treated with sulfur dioxide as a preservative, helping to kill off molds and bacteria. Sulfur dioxide is also used as a bleaching agent, as it helps lighten the color of molasses. Most brands have moved away from using sulfured molasses due to both the relatively stable natural shelf life of untreated molasses, and the 'off' flavor and trace toxicity of low doses of sulfur dioxide.