Why is my cake sticky on top after cooling?

Sugar is hygroscopic — it pulls water out of the air and out of the crumb beneath it. In a warm cake there is plenty of both. Seal that cake into a tin before it is cold and the steam it is still giving off condenses on the crust, dissolves the surface sugar, and leaves a syrup film that never quite dries. The same thing happens more slowly in a humid kitchen even to a cake that was cooled properly.

Step by step

1. Cool completely and uncovered on a wire rack.Air has to reach the top and the underside. A cake left in its tin or on a plate steams itself from below. Completely cold means cold to the middle, which for a deep cake is several hours, not forty minutes.
2. Dry a sticky top by leaving it uncovered.A few hours in a dry room usually pulls the surface back. Do not put it in the fridge — the fridge is humid and cold surfaces attract condensation as they warm again.
3. Look at the sugar in the recipe.Soft brown sugar, muscovado, honey, golden syrup, treacle and glucose all hold water far more strongly than white caster sugar. A cake built on them is going to be tacky and that is normal, not a fault.
4. Check whether you over-baked and then over-wrapped.A cake with a hard dry crust that was wrapped warm goes sticky worst of all, because there is a large moisture gradient between the dry crust and the wet crumb, and wrapping forces it to equalise at the surface.
5. Store it properly once dry.An airtight tin at room temperature for most cakes. Greaseproof paper between the cake and the lid absorbs the small amount of moisture that still moves. See `keep-baked-goods-fresh`.
6. If you need a dry surface for decorating, use a barrier.A thin brush of warmed apricot jam, or a crumb coat of buttercream, seals the crust so icing, fondant or a dusting of icing sugar does not dissolve into it.

Tips

• Meringue-topped and marzipan-covered cakes go tacky faster than any others because their surfaces are almost pure sugar. Decorate as close to serving as you can.
• If a sticky top has lifted the parchment or the cake has stuck to its wrapping, peel it while the cake is cold rather than warm — cold crumb tears less.
• A cake destined for freezing should be wrapped cold, and unwrapped while still frozen to thaw in open air, or the condensation lands on the crust as it warms.
• A gently sticky top on a ginger cake or a honey loaf is a sign of a good moist bake and improves over two or three days.

Common mistakes

• Putting a sticky cake in the fridge to dry it — Fridges are humid and cakes staling in cold air go dry in the crumb while the surface stays tacky — the worst of both.
• Wrapping in cling film while any warmth remains — Cling film traps every bit of steam against the crust. It is the single most reliable way to produce a sticky top.

If it doesn't work