Though not well known in the United States, treacle is sold in the United Kingdom and throughout many former British colonies, in two distinct varieties. Light treacle, known more familiarly as golden syrup, and black treacle, the much stronger tasting, bittersweet variety. Treacle is a by-product of the sugar refining process, it's what remains when sugar cane juice is boiled down to produce grains of sugar.
Two things have made treacle sought after in the U.S.: The fact that treacle tart is the favorite dessert of Harry Potter (it's mentioned in several books in the series) and the popularity of The Great British Baking Show (like Harry, Mary Berry calls treacle tart a favorite—absolutely scrummy, in fact). Treacle tart, features a filling of golden syrup (the light version of treacle), breadcrumbs, and lemon juice over a pastry or shortbread crust. (Some versions incorporate eggs and cream, for added richness.) Both types of treacle are used to sweeten multiple British desserts including tarts, steamed cakes and puddings (like sticky toffee pudding and Scottish clootie dumplings), biscuits (what Americans call cookies), gingerbreads, and toffees. Treacle is also used in some savory applications, like for curing bacon or glazing meats, much the way molasses is included in American barbecue sauces.
As its name implies, black treacle ($10.99, amazon.com) is much darker in color than light (golden) treacle. It's akin to American molasses, specifically the blackstrap variety, which is stronger, thicker, and more bitter than unsulfured molasses. Some even describe the taste as inky and slightly salty. The most familiar brand of black treacle is made by Tate & Lyle's, the British company famous for its golden syrup; the darker version is sold in a red tin, with the familiar lion and biblical reference ("Out of the strong came the sweetness") prominently displayed. Though golden syrup ($8.68, amazon.com) was brought to market in the late 19th century, black treacle was introduced by Tate & Lyle's many years later, in 1950.
If you've ever made caramel, you will know that as sugar melts, it goes from light amber all the way to very dark before it burns. Think of the difference between golden syrup and black treacle along that same spectrum, and you can easily imagine the difference in flavor. Because the flavor is so intense, black treacle is generally used in smaller quantities than golden syrup; in other words, a little black treacle goes a very long way. Cookbook author, Jason Schreiber includes a recipe in Fruit Cake ($18.69, amazon.com) for black fruitcake, a very dark, sticky, moist, boozy Jamaican fruitcake. Though he uses blackstrap molasses, you could easily substitute black treacle for a similarly complex, deep, delicious flavor.
Many American recipes with treacle in the title, such as this Treacle Brown Bread, call for molasses in place of the traditional British sweetener, which can be hard to track down in the States. But if you do find yourself with a tin of Tate & Lyle's treacle, try substituting it in your favorite sweets. Use golden syrup (light treacle) in place of light corn syrup, honey, or standard molasses, and black treacle in place of blackstrap molasses.
The name of the syrup itself is used to describe anything overly sweet, sentimental, or cloying, as in this unfortunate quote from the British poet John Keats: "I equally dislike the favor of the public with the love of a woman—they are both a cloying treacle to the wings of independence."
