Marble, Fruit, Chocolate, Pound, Butter, Sponge, Layered Nut etc. etc. etc. they are all delicious and so different. There are so many different types of cake with different textures, different flavours & different ways of making them. It is not surprising that cakes vary greatly in the quantities & types of their ingredients. If we break cakes down into their ingredients they usually contain fat, a sweetener, eggs and flour. Some will contain extras for example liquids & flavourings. Basically the two main sources of protein in a cake recipe are eggs & flour. I have mentioned the importance of protein in cake making in the articles Proteins and The Cupcake Stress test but I will go into it with a little more depth in this article.
Eggs, wonderful protein bombs that they are, can be the only protein source in sponge cakes. They are responsible for most of the structure of the cake (it depends on the amount of starch used) - without eggs the cake would sink. Other cakes will depend on the protein from eggs & the flour used for their structure. Most recipes have been developed around wheat flour & it's protein content of ~9 - 10%. As the protein content of gluten free flours varies considerably from ~4% to ~39% substituting a cup for cup measure of a gluten free flour into a recipe based on wheat could be a fantastic success, a complete flop or somewhere in between. Cake making is further complicated by the different protein types present in gluten free flours or more specifically the absence of gluten. Once again most recipes have been developed for use with wheat flour & it's gluten content (sometimes gluten can be a hindrance when making cakes).
In addition to the protein content of a cake, the ratio of the various ingredients to each other is going to effect the outcome of the finished cake. The table below contains the ratios (relative to butter) of the main ingredients for 3 different types of cake.
| Ingredient Ratios for different types of cakes | |||
| Ingredients | Cupcake Stress Test | Butter Cake | Pound Cake |
| Butter | 1 | 1 | 1 |
| Sugar | 1.6 | 1.2 | 1 |
| Eggs | 0.8 | 1.1 | 1 |
| Milk | 1 | 0.45 | - |
| Flour | 1.2 | 1.6 | 1 |
What do cupcakes look like when they are made using the different ratios? Of course it will depend on the flour used but as the recipes were based on wheat flour we should look at ones made with wheat first. The following photos of cupcakes are in the order; Cupcake Stress Test - 1, Butter cake - 2 & finally Pound cake - 3.
They all look like cake but one of the main differences between them is the lightness due to the added milk (liquid) in Cakes 1 & 2. The eggs, milk & flour all contribute to the overall protein content of the cake. If we remove the protein content from the flour, that is we use a starch to make the cakes, the resulting cakes look different to those made with wheat flour.
The following 3 cupcakes were made using maize starch. If a liquid is added to the recipe as in the Cupcake Stress Test or Butter cake the resulting cake either has no cake structure or has a separate layer. A cupcake sized pound cake can be made with maize starch but the cake is rather dry. The protein present in the eggs in combination with the starch is sufficient to provide structure for the Pound cake.
I find maize starch to be the "driest" of the readily available gluten free starches & tapioca starch the "wettest". If a pound cake can be made with maize starch can a pound cake be made with tapioca starch?
All of the following tapioca starch cupcakes are unappealing & none of them have a true cake structure. Although the amount of protein present in the tapioca starch pound cake is the same as with the maize starch pound cake it is not enough to provide structure.
Will adding more protein to the tapioca starch cake mix "rescue" the cake? There are many different sources of protein that can be used for example high protein flours & protein powders. How much protein is needed to "rescue" a tapioca starch pound cake? Can you put in too much protein? Flaxseed flour, lupin flour, red lentil flour & even cocoa are high in protein - certainly higher than wheat flour. Coconut flour has a protein content higher than wheat but is also a "dry" flour. Making pound cakes out of these flours without diluting the flour allows us to view the effect the protein in these flours has on cake structure.
As far as pound cakes are concerned most of those made with the undiluted flours are a massive fail. The following cakes were made with; Flaxseed flour, Cocoa, Lupin flour, Red Lentil flour & Coconut flour. Flaxseed flour & Lupin flour have protein contents above 30%. The protein content of Cocoa & Red Lentil are above 20% while Coconut flour has the lowest at 14%. The proteins present in each of the flours will be different but in all cases too much protein results in a compact cake.
What do the cakes look like if the flour has been diluted with tapioca starch? By how much do we dilute the flours? The amount of the flour used/diluted will depend on it's protein content & how the protein "behaves" when making cakes. For example Flaxseed flour has a protein content of 37% & Lupin flour has a protein content of 39% but the flaxseed flour pound cake appears to be "held together" more than the lupin flour pound cake. In this case I would use less flaxseed flour than lupin flour. As wheat has a protein content of ~10% & cupcakes can be made with a flour containing ~5% protein (chestnut flour) I use a protein content somewhere in between.
The Tapioca Flaxseed flour pound cake was made with a flour/starch mix that contains 20% flaxseed flour & 80% tapioca starch. The protein content of the flour/starch mix is 20% of 37 g/100g = 7.4 g/100g or 7.4%. The resulting pound cake was given a tick of approval by my children - it tasted good & it certainly looks better than the pound cakes made with only tapioca starch or flaxseed flour. However the cake has a slight concave top so I would dilute the flaxseed flour even further if I were to make it again.
Diluting the flour certainly helps the pound cakes structure & "rescues" the tapioca starch. Both Cocoa & Lupin flour were diluted to 25% with tapioca starch. The corresponding protein percentage of the flour/starch mix was ~5% for Cocoa & ~9.5% for Lupin. The top of the pound cake made with Lupin flour is slightly concave so the next time I make this I would dilute it to ~5% protein.
The above 5 flours when diluted all rescued the structure of the tapioca starch pound cake. For taste the Cocoa & Coconut pound cakes were the best while the Red Lentil & Lupin pound cakes were the worst tasting. Some flours have a revolting taste & need to be diluted a great deal before the awful taste dissapears. "Pure" proteins may also have a strong taste but it may not be as bad as the available flours. Can "pure" proteins from different sources also rescue the structure of a tapioca pound cake? The following tapioca pound cakes were made with different proteins diluted to ~10% protein.
I have used a number of different "pure" proteins from animal & plant sources. The majority of the pound cakes look the same with the exception of the cake made with skim milk powder. Skim milk powder is ~33% protein (not pure) & ~66% lactose, the lactose increases the overall sugar concentration of the cake & changes the cake from a pound cake to something closer to a cupcake stress test cake.
The first cake contains egg white powder, the second gelatine & the third pea protein. The gelatine I used was powdered I believe the cake would have tasted better if sheet gelatine was used. Of these three cakes the first was the best tasting & the cake made with pea protein the worst. Below are pound cakes made with tapioca starch & whey protein (left) or skim milk powder (right).
Looking at the different pound cakes above it is easy to see the effect protein has on cake structure. It doesn't seem to matter the type of protein, whether they are "pure" protein or protein from a gluten free flour, they all seem to help with cake structure. Too much protein has a detrimental effect so how much is too much? As most of the cake recipes available have been based on the use of wheat flour with it's protein content of ~9 - 10% you don't need to add more than 10% protein. A bit of trial & error is needed when determining how little protein you need to add. Below are a series of photos of Lupin flour pound cakes containing decreasing amounts of lupin flour.
100% Lupin flour contains 39 g/100g of protein while 50% contains 19.5 g/100g of protein.
25% lupin flour contains 9.75 g/100g of protein - this is similar to wheat flour. There is 5.9 g/100g of protein in 15% lupin flour.
The final cake in this series is made with 10% lupin flour (3.9 g of protein/100g). For this type of cake 10% lupin flour contains sufficient protein to give the cake structure.
The amount of protein needed in a gluten free flour mix will depend on the type of cake being made but as a general rule it will be between 4% - 10%.