The difference between light brown sugar and dark brown sugar is an interesting topic, because many recipes do not actually specify which one to use.

This begs the question, are they always interchangeable, then?

The answer is yes, for most dishes.

All brown sugar is white sugar that has had a small amount of molasses added to it; molasses is a thick syrup produced during the refining of sugar. Light brown sugar simply has less molasses in it than dark brown.

When recipes do call for a specific type of brown sugar, it is because of the flavors they add to the dish, not because of the way they function – this is unlike baking soda and baking powder, which have nothing to do with flavor and everything to do with the mechanics behind the baking.

On Domino Sugar’s website, they helpfully list which sort of foods go better with one or the other:

• Light brown sugar: cookies, shortbread, spiced cakes, brownies, crumble toppings
• Dark brown sugar: coffee or chocolate cakes, fudge, barbecue sauce, marinades, sweet and sour sauce, pancake syrups

As one might expect, dark brown sugar contains a richer flavor, while light brown is milder. Therefore, some maintain (and I agree) that lighter brown sugar is the safer bet. 

According to my Food Substitutions Bible, you can adjust substitutions for brown sugars in the following ways:

• 1 cup granulated sugar + 1 to 2 tbsp molasses = 1 cup light brown sugar
• 1/2 cup dark brown sugar + 1/2 cup granulated sugar = 1 cup light brown sugar
• 1 cup light brown sugar + 1 tbsp molasses = 1 cup dark brown sugar

But, who has molasses hanging around in their kitchen? I don’t.

Again, for most cooking and baking purposes, you can interchange light brown sugar for dark and vice versa. I typically always have light brown sugar on hand and would only purchase the dark if a recipe clearly called for it.

The substitutions bible additionally provides a couple of extra helpful tips:

• To keep light brown brown sugar soft, store it in a resealable plastic bag with a strip of orange zest.
• Always pack light or dark brown sugar tightly in the measuring cup in order to get an accurate measurement.