There are many varieties of brown sugar, but light and dark brown sugar are the best known easiest to find. Both are chemically similar and are made using the same processing methods; however, they are two completely different products. If you are faced with a choice between them, you will want to weigh their differences carefully before deciding. The light vs. dark brown sugar SPICEography Showdown below can help.
How does light brown sugar differ from dark brown sugar?
Light brown sugar and dark brown sugar differ in appearance and that difference has to do with molasses content. Molasses is the dark brown, viscous byproduct from processing sugarcane juice to promote sugar crystallization. To make brown sugar, the sugar is refined and some of that molasses is returned to it to make the sugar brown. The amount that is returned to the sugar crystals is what determines whether you get light or dark brown sugar. Light brown sugar has less of it; dark brown sugar has more.
The lower proportion of molasses in light brown sugar means that it has a milder flavor, while dark brown sugar has a more intense flavor. Since molasses is a liquid, more of it means that the sugar will be moister and less of it means that the sugar will be dryer.
Can you use light brown sugar as a substitute for dark brown sugar and vice versa?
Light brown sugar can be used in most recipes that require dark brown sugar. Both will provide the same amount of sweetness, so you can switch them out to increase or decrease the molasses flavor to your liking. If you want to make a substitution while being faithful to the recipe, you will have to make an effort to simulate the brown sugar you are replacing. For example, you can add molasses to light brown sugar to replicate the darker color and deeper flavor of dark brown sugar. Without the addition of molasses, light brown sugar will not make an effective substitute. It is too pale and will be lacking in flavor.
Similarly, dark brown sugar can be used as a substitute for light brown sugar if you add some refined white sugar to dilute the molasses flavor and color. Dark brown sugar will not be a good light brown sugar substitute without the addition of white sugar. It will make most baked goods too dark and (in some cases) too bitter. You will also need to consider moisture; the lack of moisture in light brown sugar or the added moisture in dark brown sugar can affect the extent to which a cake rises.
When should you use light brown sugar and when should you use dark brown sugar?
Use light brown sugar when you need a little molasses flavor and a light brown color. One classic use is in chocolate chip cookies, another is in pineapple upside down cake. Similarly, you can add it to mildly flavored cereals and to coffee. In most of these applications, too much molasses would make the food items unattractively dark or unpalatable.
Use dark brown sugar when you want the deep molasses flavor and in foods where a deeper brown color is desired. Barbecue sauces are one area where a darker brown is usually better. Note that if a recipe requires brown sugar without stating the type, you will want to use light brown sugar in almost all cases.