What's the difference between a vegan cake and a non-vegan cake? It's a great question.
Traditionally, cakes were made from flour, sugar, butter and eggs. Many of us may have baked with our mums and grans, or our dads and grandads, when we were little, and used the 'creaming method'. This, as those who didn't have an electric mixer will recall, involved 'creaming' together equal weights of butter and sugar in a mixing bowl until the mixture had gone from a buttery yellow to a much paler colour, with a fluffy texture. Without a mixer, it took ages! The aim was to soften the butter, and beat air into the butter and sugar mixture.
Once you had done this, it was time to add the eggs. Now, you would add one egg at a time, and two teaspoons of your flour, and beat it into the butter and sugar. This took some elbow grease, too, and the aim was to beat air into the mixture, with the egg mixing in and allowing the batter to trap very fine air bubbles. Once the mixure was smooth again, you would repeat the process with the next egg, and the next.
Then, final stage, you would 'fold' in the flour and baking powder to the egg, butter and sugar mixture. This was done carefully, with a metal spoon, and you were supposed to do it gently by folding the mixture over itself in the bowl in circular motions, or a figure of eight. I wasn't very patient, and I often hurried, but it didn't really seem to matter (though maybe if I'd had more patience my cakes would have been lighter).
Then you'd pour your lovely smooth cake mixture into tins and bake it in a preheated oven until you could gently press the top of the sponge and it would rebound, or a knife stuck into it came out clean. This part doesn't change for vegan cakes!
How does making a vegan cake differ from making a tradtiional cake by the creaming method? For one thing, it's simpler. And for another, it is much easier, there is far less elbow grease involved, no beating and no creaming!
There are a few ways to make a vegan cake, and the very first question anyone asks is almost always, "What do you use in vegan cakes instead of eggs?" Eggs, it turns out, are not in any way necessary to make a light, moist sponge cake! Do you need something to replace the eggs? No, you don't. You don't need an egg-replacer, as such. I think the reason for this is that you don't use the creaming method for vegan cakes. You don't need to start by combining the sugar and butter, and then beat in an egg alternative. The method for baking vegan cakes is completely different.
Usually, vegan cakes are made using the simple method of putting all the "wet ingredients" into one bowl, and all the "dry ingredients" into another. Then, at the last minute, you pour the wet into the dry, mix it all up into a smooth batter, and pour it into your cake tins, to go straight in the oven. This is a wondefully straightforward way to make a cake. It gives you plenty of time, because all the magic happens once you have mixed up the wet and dry ingredients. It involves no hard physical work (beating away with a wooden spoon) and you don't need a mixer. You can just use a spoon or a whisk until you get a smooth mixture, and your work is done!
Why combine wet and dry at the last minute? Another good question! The reason is that, with vegan cakes, the raising of the sponge texture is created by a chemical reaction, and not by a combination of mechanical and chemical actions. In vegan cakes, the reaction between the acid and alkaline ingredients which creates gas bubbles in the mixture (carbon dioxide) is initiated when water is added by the wet ingredients. This can be either through one of the wet ingredients containing acid directly (such as vinegar or lemon juice); or it can be because the acid present in the baking powder only begins to react with the alkali in the baking powder in the presence of liquid.
Baking powder is normally made of sodium bicarbonate (alkali) plus an acidic salt such as calcium phosphate or tartaric acid (cream of tartar) in a carrier powder such as cornstarch or sometimes wheat flour.
Either way, once liquid is added, the chemical reactions start, gas is generated in the mixture, and this is what will cause your cake to rise beautifully. You can see the bubbles forming if you watch for a minute or two after you've mixed everything together. The bubbles will rise to the top of your mixture. If you've aleady poured your mixture into your tins, now is the time to get them in the oven. If not, get pouring and get them in quickly! As your cakes begin to cook, the air bubbles will remain captured in the sponge matrix as it solidifies, and your cake will have a lovely spongey texture.
Is the structure of a vegan cake different?
There is a little bit of difference in the texture of vegan cakes versus non-vegan cakes made with eggs and butter. Vegan cakes are just a little softer in texture. This is not noticable in ordinary eating situations! Really, the only difference it makes is when you are stacking a cake, for example for a vegan wedding cake. Vegan sponge is a little less 'structural' so it just means it's slightly less resilient for building tall structures or intricate cake shapes. This is more of a techinical consideration for cake bakers, rather than anything worry about for just enjoying your cake.
A consideration with regard to the texture of vegan cakes is which non-dairy milk you use in making your cake. Soya milk gives the best texture and structure of your sponge. Oat, hemp and coconut milks give less structural stability, perhaps because they are lower in protein than the soya beans used for soya milk. This means that, again, when using your cake to stack or building a shaped cake, a soya-free sponge will be more tricky to work with and won't cut so neatly as cake baked with soya milk.
What about vegan buttercream?
A great question. Vegan buttercream is very similar to non-vegan, now that there are some superb vegan butters on the market. Vegan buttercream compared with dairy-butter buttercream is slightly softer in texture, and it's a little more difficult to achieve a really fine and perfect finish with vegan buttercream.