Demerara vs muscovado sugar
Both are called raw or unrefined and they behave as differently as any two sugars on the shelf — one is a topping, the other is a flavour.
The short answer
Demerara is large, hard, dry crystals with a thin film of molasses: it survives a bake intact, which makes it a topping sugar and a poor choice inside a mixture. Muscovado has never had its molasses removed: it is fine, wet, acidic and strongly flavoured, and it belongs inside a mixture where those things are wanted. Treating them as interchangeable 'brown sugars' is the mistake.
Where they differ
| Dimension | First | Second |
|---|---|---|
| Crystal | Large, hard, dry. | Fine, soft, distinctly moist. |
| Molasses | A film on the outside. | Never removed. Distributed throughout, and several times as much in the dark grade. |
| Dissolving | Resists it, deliberately. | Readily. |
| Inside a creamed cake | Poor — gritty patches and weak aeration. | Works, and makes the cake denser, darker and softer. |
| As a topping | Excellent. This is what it is for. | Useless — it melts into the surface. |
| Acidity | Slight. | Noticeable, and enough to matter where bicarbonate of soda is the leavener. |
Neither is a straight swap for soft brown sugar
Most soft brown sugar is refined white sugar with molasses added back, which puts it between the two: finer and wetter than demerara, milder and drier than muscovado.
Going from soft brown to muscovado makes a bake darker, softer, more acidic and more strongly flavoured, and in a bicarbonate-leavened recipe it can change the rise. Going from soft brown to demerara mostly fails: the sugar does not dissolve and does not cream.
The labels do not help. 'Raw', 'unrefined' and 'natural' are used across all of these and describe processing rather than behaviour.
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