Guinness Cake Using Melted Chocolate

Our answer

We would not recommend using melted chocolate instead of cocoa powder when a recipe specifies the powder, and also would not recommend using cocoa powder when a recipe specifies melted chocolate. Unsweetened cocoa powder is almost all cocoa solids whereas dark chocolate is usually 50-70% cocoa solids and also contains cocoa butter, sugar and sometimes vegetable fats. Cocoa powder also tends to give a deeper, richer chocolate flavour in cakes and you would need to use more chocolate to try and compensate.

The difference in the composition of the two and the quantity used can have an effect on the texture of the cake. It can increase the water content of the cake, making it tougher, and also changes the fat content and mixture. In particular cocoa butter tends to be solid at room temperature, vs. oil which is liquid at room temperature and butter which is soft at room temperature. This can make the cake feel more dry and crumbly when you eat it, unless you serve the cake warm.