Molasses produced for human consumption in the United States is made from sugar cane. The two main tasks required to make molasses from sugar cane are to separate out the sugar cane juice from the pulp, and then to extract the sugar (mostly sucrose) from the juice. What's called molasses is the syrup that remains after the sugar has been extracted from the juice.
It's not that easy to extract all of the sucrose from sugar cane juice. After a first round of processing, which involves spinning the juice in a centrifuge and heating (boiling), you can get a lot of the sucrose out, but not all of it. The syrup that remains after this first round of processing is the light molasses you see in the grocery store. It's also called "first" molasses and has the mildest taste of any molasses. Another round of processing is needed to further extract more sucrose. (The removal of sucrose from the molasses syrup is not all that significant on the nutrition side of things, but it is important to the manufacturer on the economic side because the removed sucrose can be further processed and sold as table sugar). This second round of processing further concentrates the syrup and also darkens it, resulting in the dark molasses you find in most grocery stores. Dark molasses is also called second molasses.
A third round of processing is possible, and this is the round that results in the product known as blackstrap molasses. Blackstrap molasses is the thickest form of molasses, the darkest, and the most dense in terms of minerals. Three rounds of heating are the reason for the very dark color of blackstrap molasses, because even though many sugars have been removed from the syrup, the sugars that do remain get caramelized from three rounds of heating. Sometimes you'll only find blackstrap molasses in natural foods stores. Because of the superior mineral content of blackstrap molasses we prefer this version of the product. You'll find significant amounts of calcium, copper, iron, magnesium, manganese, potassium and selenium in blackstrap molasses.
A secondary issue is related to the use of sulfur during sugar cane processing. Sulfur dioxide can be used for a variety of reasons during the processing of sugar cane or the production of molasses. Most commonly, sulfur dioxide is used to lighten the color of the molasses or to help extend its shelf life. It may also be used to help with the processing of sugar cane when the cane has been harvested at an early stage. We've been unable to find research studies showing direct benefits or direct health risks in connection with the sulfuring of molasses. In principle, it would make sense to us that a sugar cane allowed to sun-ripen and develop would make for a more natural food product than a sugar cane that was harvested at an early stage. We do know that there is a relationship in sulfur metabolism between sulfur dioxide and sulfites, and that sulfur dioxide has been identified as a key problematic substance involved with allergic reaction to sulfite in foods. This connection between sulfur dioxide and food sulfite reactions raises some questions for us about the desirability of a food processed with the addition of sulfur dioxide.
In addition, on the environmental side, we know that sulfur dioxide is a primary component in the production of acid rain, and is a pollutant of enormous concern to environmental scientists. The idea of a sugar cane processing facility releasing more sulfur dioxide into the air is not one we like from an environmental perspective.
To summarize, we recommend organic, unsulphured blackstrap molasses as the molasses of choice. There is good research showing the superior nutrition provided by blackstrap versus light or dark molasses. There is not good research showing the benefits of unsulphured molasses in any form. However, there is reason to suspect potential health risks related to sulfite allergy and use of sulfur dioxide in food processing. There is also an environmental reason to avoid purchasing a sulphured molasses product, notably the contribution of sulfur dioxide to the production of acid rain.
For more information on this topic, see:
Sugar Processing Research Institute. (2001). Technical Report Nr. SPRI 2001-2The Effects of Sulfur Dioxide in Sugar Processing Comparing Model Sucrose and Cane Juice Systems.
Gilbert RA, Shine Jr JM, Miller JD, et al. (2004). Sucrose accumulation and harvest schedule recommendations for CP sugarcane varieties. University of Florida Cooperative Extension Service Fact Sheet SS-AGR-221. University of Florida, UF/IFAS Extension Digital Information Source (EDIS) Database.
World Health Organization. (1974).Sulfur dioxide and sulfites. Toxicological evaluation of some food additives including anticaking agents, antimicrobials, antioxidants, emulsifiers and thickening agents. Seventeenth Report of the Joint FAO/WHO Expert Committee on Food Additives, FAO Nutrition Meetings Report Series, No. 53.