What is the difference between Dutch-process and natural cocoa?

Natural cocoa is acidic. Dutch-process cocoa has been treated with an alkali to neutralise that acidity. The difference changes colour, flavour and — critically for baking — how the cocoa reacts with raising agents.

Natural cocoa is simply roasted, ground cocoa beans with most of the fat pressed out. It is acidic, with a pH around 5 to 6, lighter reddish-brown, and tastes sharp and intensely chocolatey with fruity notes.

Dutch-process cocoa — the process was developed by Coenraad van Houten in the Netherlands in the 1820s — is washed with a potassium carbonate solution. This raises the pH to around 7 or 8, darkens the colour to deep brown or almost black, and produces a smoother, mellower, less sharp flavour. It also dissolves more readily in liquid, which is why it is preferred for hot chocolate.

The baking consequence is the part that catches people out. Bicarbonate of soda is a base and needs an acid to react and produce lift. Natural cocoa supplies that acid. Baking powder contains its own acid and does not need one.

So a recipe calling for natural cocoa and bicarbonate of soda will underrise if you substitute Dutch-process, because the acid the bicarbonate needed has gone. A recipe using Dutch-process and baking powder is more forgiving.

As a rough guide: if the recipe uses bicarbonate of soda alone, use natural cocoa. If it uses baking powder, use Dutch-process. Where the recipe specifies, follow it.

This is also why old-fashioned red velvet cake was reddish — natural cocoa's acidity reacting with the batter, long before food colouring was added.