How to Replace Baking Powder with Bicarbonate of Soda in a Cake

The cake is nearly ready, the oven is heating up, and butter has left a glossy mark on the worktop… then, at precisely that moment, the baking powder tub turns out to be empty. We all know this minor disaster, often on a Sunday or just before guests are due to arrive. There may be a packet of bicarbonate of soda waiting in the cupboard, somewhat forgotten behind the vanilla sugar. The good news is that it can rescue the recipe, provided you do not add it at random. Bicarbonate of soda does not work independently in the way baking powder does. It needs an acidic partner and a fairly accurate quantity. Your cake can still be soft, risen and light; you simply need to understand one very straightforward principle.

Bicarbonate of soda can raise a cake, but it cannot do everything

Baking powder and bicarbonate of soda look similar, particularly when stored in small white sachets, yet they work differently. Baking powder already includes bicarbonate of soda, one or more acidic agents, and often a little starch to keep the mixture stable. Bicarbonate of soda, on the other hand, is on its own: it must meet an acidic ingredient before it releases the carbon dioxide bubbles that make a batter rise. Without this reaction, the cake remains dense, sometimes rather disappointing, and can develop a distinctly unpleasant flavour.

Plain yoghurt, buttermilk, lemon juice, white vinegar and natural non-alkalised cocoa can all provide that acidity. Take a classic yoghurt cake: if the recipe calls for one sachet of baking powder, the yoghurt already creates suitable conditions for bicarbonate of soda. You can use around half a teaspoon of bicarbonate of soda instead of a standard 11-gram sachet, depending on the true acidity of the other ingredients. The batter must then go straight into the oven. Those bubbles will not wait.

Getting the amount right is crucial because bicarbonate of soda is remarkably powerful. A quarter of a teaspoon of bicarbonate of soda can replace one teaspoon of baking powder when the recipe contains sufficient acidity. This is not a magic formula to follow blindly: a lemon batter is better suited to it than a very neutral pound cake. In baking, a small difference is often more noticeable in the taste than in the appearance. Too much bicarbonate of soda leaves a metallic or soapy note, which is hard to disguise, even beneath a generous layer of chocolate.

A simple method to avoid a soapy taste

Before substituting baking powder, first identify the acidic ingredients already included in the recipe. For every missing teaspoon of baking powder, combine a quarter of a teaspoon of bicarbonate of soda with half a teaspoon of cream of tartar, if you have some. If there is no cream of tartar, add roughly one teaspoon of lemon juice or white vinegar, removing the same amount of another liquid from the recipe. The vinegar disappears during baking: nobody will detect that it was ever in the cake.

The most common mistake is swapping baking powder for exactly the same quantity of bicarbonate of soda. It is an easy error to make, especially when you are cooking in a hurry and a child is already asking when their tea-time treat will be ready. Yet one whole teaspoon of bicarbonate of soda in a small loaf cake can ruin everything. Let us be honest: nobody really does this every day, and even careful cooks can confuse the two powders. It is better to use too little than too much: a cake that rises slightly less is far more enjoyable than one with an aggressive flavour.

Once the wet and dry ingredients have been brought together, put the batter in the oven promptly rather than leaving it on the worktop for ten minutes while you look for a tin. The reaction begins as soon as the bicarbonate of soda comes into contact with the acid.

“Bicarbonate of soda is an excellent stand-in, as long as you give it an acid and do not use too heavy a hand.”

Keep this reminder beside the mixing bowl:

• 1 teaspoon of baking powder = around 1/4 teaspoon of bicarbonate of soda;
• add an acidic ingredient that suits the recipe;
• bake immediately after mixing.

Cakes best suited to bicarbonate of soda, and those best left alone

Yoghurt cakes, fruit muffins, brownies, lemon loaves and buttermilk bakes are the easiest options to get right. Their recipes already contain, or readily accommodate, a touch of acidity. Berries, apple purée and molasses can help too, although their effect is less predictable than lemon juice. For a chocolate cake, check the wording on the cocoa packet: natural cocoa is acidic, whereas alkalised cocoa is far less so. That tiny detail can alter the finished texture.

A very airy sponge, a génoise, or any recipe whose volume depends chiefly on whisked egg whites requires greater care. Bicarbonate of soda cannot replace technical baking methods or the air incorporated by whisking. Nor can it stand in for baker’s yeast in brioche, pizza or bread: in those cases, fermentation and time do the work. The right substitution depends on the cake, not merely on the missing ingredient. A straightforward recipe will often tolerate improvisation; a demanding batter will not.

There is something reassuring about this small trick, too: it is a reminder that a kitchen cupboard is not a fixed laboratory. You can observe the batter, notice its lemony aroma, make sensible adjustments and record what worked. A slightly more rustic cake, served warm with a coffee, can sometimes leave a better memory than a dessert that looks perfect in a photograph. The next time baking powder is missing, bicarbonate of soda will no longer be a mysterious emergency substitute, but an ally to use in moderation.