Molasses as you know is a by-product of the sugar making process. It can be made from either cane or beets, though beet molasses isn’t used much here in States (Europeans do use it some, however). As was mentioned in the sugar posts from last week, sugar is made by adding “seed” crystals to a volume of long-cooked, drastically reduced cane juice. The mixture forms crystals and the whole mess is then spun in a centrifuge (basically a big basket lined with cloth) and the thick liquid molasses is pulled out via centrifugal force.
All molasses has at least some uncrystallized sucrose in it since the crystallization process is never entirely successful. It also has plenty of other stuff: long-chain (non-sucrose) sugars, proteins, minerals, and bits of cane plant. The extended cooking of the juice browns the plant bits and caramelizes some of the sugars, and those are what give the molasses its color.
The cooking also does something else: it creates invert sugar. Cane juice is acidic to begin with, but only becomes more so as it cooks, since the brown, broken molecules that result from caramelization are also acidic. Combine that with heat and sucrose and you get a sucrose-glucose-fructose syrup that’s remarkably resistant to crystallization.
The act of crystallizing and centrifuging sugar is called a “strike” in the industry. The molasses that the “first strike” produces is called, unsurprisingly, “first strike” molasses, or more succinctly “first” molasses. It’s the lightest and sweetest of the three molasses varieties as it contains the most residual uncrystallized sucrose. It’s sometimes called “Barbados” molasses.
If that batch of first molasses is subjected to a second strike, the result is “second” molasses, which as you might expect, is a bit darker and less sweet. After that there is often a third strike, which removes virtually all the remaining sucrose. What’s left is a highly concentrated goo of complex long-chain sugars (which because of their molecular configuration don’t taste especially sweet on our tongues) and assorted and sundry browned stuff. This is what’s known as “black strap” (stroop) molasses. It’s the cheapest of the three, but also has the most nutrients (especially iron).
Molasses was the corn syrup of the industrial age, but does have a very strong flavor relative to corn syrup, which is why we tend not to use it so much anymore.