Brown sugar vs white sugar
Not the same sugar with flavour added. The molasses makes brown sugar acidic and water-holding, which changes leavening and texture as well as taste.
The short answer
Swapping them by weight works and does not give the same result. Brown sugar brings acidity, which can participate in a bicarbonate-based leavening system, and holds water, which makes the bake softer and chewier and slows staling. White sugar brings neither, which is why the same cookie recipe gives a chewy result with one and a crisp one with the other.
Where they differ
| Dimension | First | Second |
|---|---|---|
| What it is | Sucrose with molasses retained or added back. | Refined sucrose. |
| pH | Acidic, from the molasses. | Effectively neutral. |
| Moisture behaviour | Hygroscopic — holds water, keeps bakes soft, slows staling. | Does not hold water in the same way. |
| Effect on a cookie | Chewier, softer, slightly less spread. | Crisper, with more spread at the same weight. |
Differences that do not matter
These are real distinctions that are unlikely to change your decision. They are listed so you can stop thinking about them rather than left out so the comparison looks decisive.
- Sweetness. Broadly comparable by weight. Broadly comparable by weight.
When the swap actually breaks something
Most of the time it changes texture and flavour and nothing fails. The exception is a recipe leavened with bicarbonate of soda where brown sugar is one of the few acid sources.
Remove that acid and some of the bicarbonate has nothing to react with. The bake rises less and can carry a soapy, metallic taste from the unreacted leavener — which is a chemistry failure rather than a preference, and the reason this comparison is worth more than a note about flavour.
Related
Compares
The side that carries molasses, and therefore the acidity and the water-holding.
The refined reference the comparison is against.
The product where the difference is most visible: the same recipe gives a chewy result with one sugar and a crisp one with the other.
Covered in
Chewy, crisp or cakey: what actually decides a cookie’s texture
Where the brown-sugar-makes-chewy claim is examined. Real, and smaller than bake extent.