Treacle by John Spottiswood.

Sugar is made by extracting juice from sugar cane or sugar beets, boiling them, and then extracting the sugar crystals. Molasses is the thick, syrupy residue that's left behind in the vats. It has a sweet, distinctive flavor, and it's a traditional ingredient in such things as gingerbread, baked beans, rye bread, and shoofly pie. There are several different varieties. Light molasses= sweet molasses = mild molasses = Barbados molasses is taken from the first boiling. It's the sweetest and mildest, and is often used as a pancake syrup or a sweetener for beverages. Dark molasses = full molasses = full-flavored molasses is left behind after the juices are boiled a second time. It's less sweet but more flavorful than light molasses, and it's a good choice if a recipe simply calls for molasses. Blackstrap molasses comes from the third and final boiling. It's too strong and bitter for most recipes, and it's mostly consumed for its alleged nutritional benefits. Most of the molasses sold in supermarkets is unsulfured. Sulfured molasses has sulfur dioxide added as a preservative, and isn't as mild and sweet as unsulfured molasses. Food grade molasses is almost always made from sugar cane. Sugar beet molasses is very bitter and is mostly used as cattle feed or as a medium for growing yeast. When measuring molasses, grease the cup and utensils to keep molasses from sticking. If your molasses crystallizes while being stored, heat it gently to dissolve the crystals. After opening, you can store molasses in your cupboard.