Many recipes call for “brown sugar” without specifying light or dark. Is there a difference between light brown sugar and dark brown sugar? Does it matter which one I use?
Yes, there is a difference between light brown sugar and dark brown sugar, but you can make substitutions if you only have one type on hand.
The “brown” in these sugars is a carefully designed form of molasses, added at the end of processing (rather than leftover from the beginning, as many people seem to think). It’s essentially a coating, thicker in dark brown sugar and thinner in light brown sugar. The coating adds moisture — brown sugar can contain as much as 35 percent more water than white sugar — and it traps air, so brow sugar is fluffier. That’s why measurements generally specify “packed.”
If the recipe doesn’t say which to use, it probably doesn’t matter. If you need to substitute, try to balance the molasses, adding ¼ teaspoon or so per cup. when using light sugar for dark. If the recipe calls for light but dark is all you have, use a packed 2/3 cup dark and 1/3 cup white for every packed cup of light sugar needed.