Pour juice into a small heavy-bottomed pot. Bring to a low boil over medium to medium-high heat. Adjust heat as needed to maintain a low boil.
At about 30 to 35 minutes, you’ll notice the liquid is taking on a syrupy texture and that it’s becoming bubblier. At this point, the transition from syrup to molasses happens quickly. Watch closely and keep testing with a spoon.
As it becomes syrup, it will start coating the spoon. As it becomes molasses, it’ll have an even heavier coating. Better to take it off the stove too early than too late. If it’s too liquidy, you can boil it down a bit more, but you can’t reverse the process if it’s too thick or burnt.
The whole process will take between 30 and 40 minutes (closer to 40). You can be more aggressive with the heat to speed up the process. Pay close attention near the end because as it gets syrupy, it can burn and over-reduce very quickly.
Store the molasses in an airtight container in a cool, dry place, where it will keep for a while.
--Beth Lee of the blog OMG! Yummy