Do I need the vinegar in the Dark And Sumptuous Chocolate Cake? What's it for?
Nigella's Dark And Sumptuous Chocolate Cake (from SIMPLY NIGELLA) is a vegan chocolate cake, so it doesn't contain any eggs or dairy ingredients. Often for cakes eggs act as one of the leavening agents, helping the cake to rise. For this cake the leavening agent is just bicarbonate of soda (baking soda).
However bicarbonate of soda is an alkali and needs an acid to react with so that it creates bubbles of carbon dioxide that make the cake rise. Some cake recipes with bicarbonate of soda include acidic dairy ingredients, such as buttermilk or yogurt. But as this cake does not contain any dairy ingredients acid is added in the form of vinegar instead, which does not affect the taste of the finished cake. Without the vinegar the cake will not rise and will have a very dense texture.