What is blackstrap molasses?

What is blackstrap molasses? My jar of imported blackstrap lists its calcium content as 6% of the recommended daily allowance and its iron content as 15.3%.

While there are several types of molasses, only two are widely available: one that’s extracted early in the sugar-refining process and one that’s extracted toward the end. The first contains small amounts of minerals and lots of sugar and is used to make that pantry staple, fancy molasses. The molasses extracted at the end of the refining process is blackstrap. Much darker and more strongly flavoured than fancy molasses, it is also more nutritious: for the brand we checked, 15 ml (1 tablespoon) of blackstrap molasses contains 180 mg of calcium (16% of the recommended daily value) and 3.6 mg of iron (26% of the recommended daily value). On the other hand, the same amount of fancy molasses contains only 44 mg
of calcium and 1 mg of iron.