What ingredient softens brown sugar?

The ingredient that softens brown sugar is moisture.

Here's why:

* Brown sugar contains molasses. This makes it naturally more hygroscopic (attracts moisture) than white sugar.

* Over time, brown sugar loses moisture and hardens. This is why it's important to store it properly.

* Adding moisture can rehydrate the sugar. This can be done by:

* Adding a slice of bread: The bread absorbs the moisture from the air and softens the sugar.

* Placing a damp paper towel over the sugar: The paper towel will release moisture and soften the sugar.

* Microwave it: Placing a bowl of brown sugar in the microwave for a few seconds can soften it.

So, while there's no specific ingredient that directly "softens" brown sugar, it's the addition of moisture that brings it back to its soft and pliable texture.