Which sugar should I use for which bake?

Two properties do nearly all the work. Crystal size decides whether the sugar can cut air into butter and whether it dissolves in the liquid available — fine caster does both well, coarse demerara does neither. Molasses content decides how much moisture the sugar holds, how acidic it is, and how dark the bake goes. Once you know which property a recipe is relying on, substituting becomes a judgement rather than a gamble.

Step by step

1. Ask what job the sugar is doing.Aerating with butter, dissolving into a meringue, providing chew, providing crunch on top, or providing sweetness alone. That decides the sugar far more reliably than what the recipe happens to say.
2. Use caster wherever creaming or whisking is involved.Creamed cakes, meringues, whisked sponges. Fine crystals mean more cutting edges per spoonful for aerating, and full dissolution so nothing is gritty.
3. Use brown sugar deliberately, not as a default.It brings moisture, chew, colour and a distinct flavour, and it is acidic — which matters if the recipe uses bicarbonate of soda, because that reaction needs an acid. Swapping white for brown in a bicarb recipe can leave a soapy taste.
4. Substitute by weight, not by volume.Brown sugars pack differently from white and a cup of one is not a cup of the other. Weight substitution is close to one-for-one between caster, granulated and soft brown.
5. Adjust liquid when you swap in a syrup.Golden syrup, honey and treacle are roughly 20 per cent water. Replacing dry sugar with syrup means reducing the other liquid, and the bake will brown faster and stay softer.
6. Do not cut sugar without expecting consequences.Sugar is structural. It holds moisture, tenderises by interfering with gluten, browns the crust and stabilises meringue. A 25 per cent reduction is usually fine; halving it changes the bake substantially. See `reduce-sugar-and-salt-in-cooking`.

Tips

• Golden caster sugar behaves exactly like white caster with a slight caramel note. It is a straight swap.
• Hard brown sugar softens in a sealed container with a slice of bread or apple overnight, or in twenty seconds in the microwave with a damp piece of kitchen paper.
• Vanilla sugar — a used pod buried in a jar of caster — costs nothing and is genuinely worth having.
• Sugar substitutes based on erythritol or stevia do not caramelise, do not hold moisture and do not stabilise meringue. Bakes made with them behave very differently and need recipes written for them.

Common mistakes

• Creaming with granulated or demerara — Coarse crystals aerate less and may not dissolve, so the cake is denser and can be gritty. Caster is the right tool.
• Swapping white for brown in a bicarbonate recipe without thinking — It changes the acid balance. Going the other way — brown to white — can leave unreacted bicarbonate and a soapy taste. See `fix-a-soapy-tasting-cake`.

Alternatives

• Caster sugar: Fine white crystals. The default for creamed cakes, meringues and most biscuits, because it aerates butter well and dissolves fully. Blitz granulated in a processor if you have run out.
• Granulated sugar: Coarser white crystals. Fine for melted-butter recipes, crumbles and general sweetening; it aerates less well and can leave a gritty note in a low-liquid cake.
• Soft light and dark brown sugar: Caster-sized crystals with molasses added back. Holds moisture, so gives chewier biscuits and moister cakes; acidic, so it reacts with bicarbonate of soda. Dark is stronger and more treacly.
• Muscovado: Unrefined, sticky, strongly flavoured. Excellent in gingerbread, fruit cake and sticky toffee; too dominant in a plain sponge and it clumps, so break it up before use.
• Demerara: Large hard golden crystals. A topping sugar — it stays crunchy through a bake. It does not cream and does not dissolve reliably in a batter.
• Icing sugar: Powdered, with a little anti-caking starch. For icings, dusting and very short biscuits where you want no crystal structure at all. It aerates almost nothing.
• Golden syrup, honey and treacle: Liquid sugars. They add moisture and browning, hold water so bakes stay soft, and need the liquid in the recipe reduced if you swap them in for granulated sugar.