Blueberry Chiffon Cake : Analysing The Science Behind Baking With Egg White

The chiffon cake is one of my favourite cake simply because the texture is so light and divine. In addition, if one were to scrutinise the recipe, you will find that it is primarily made up of egg whites, very little flour, very little oil(not butter) and very little sugar. Overall, a healthier cake that can be enjoyed with less guilt.

However, any recipe that hinges heavily on the way egg white behaves usually appears to be shrouded in a cloak of mystery. Examples include Souffles and Macarons. To get successful results in making these dishes, the right Meringue stability is imperative.

When baking the Chiffon Cake, I insist on being a purist. I refuse to use baking powder to inflate the cake- I stubbornly feel that that is cheating. I am fine with using natural ingredients to stabilise the egg white and there are a couple of ways to do so.

The egg white is comprised of protein chains and water. It's behaviour is very similar to a soap solution - which is made up of organic chains and water.
Whipping the egg white introduces air into the system. The foam that forms is similar the foam one gets from agitating soap with water. What is happening at the molecular level is that the protein chain in the egg white will form a 'membrane' that traps air. Part of the protein chain bonds with water and part of it repels water. Hence the 'membrane' is essentially the water-air border in the system. The stability of the foam depends on how resilient this 'membrane' is. Smaller bubbles form more stable foam. However, if the membrane is disturbed, small bubbles will merge to form big bubbles and this eventually will lead to bubbles bursting.

When Are Egg Whites Whipped Enough?
For chiffon cake, I like to whip the egg whites to firm but not spiky stiff peaks. When I overturn my bubble whip, the tail of the meringue will still droop a little. However, the meringue should be firm enough to support the weight of the whip. I check by sinking my whip into the bed of meringue, it should stand firm on its own without falling over. Whipping it to short stiff spikes may also work but you will find that the texture of the cake to be drier. What About Salt or Acid? Adding a little salt (added with sugar during whipping process) or adding a little acid helps to stabilise the egg white foam. The positive ions ( hydrogen ions in acid) prevent the protein molecules from folding up. When the protein molecules folds up into a ball, it will not be able to spread out and stabilise the 'membrane'. Most people like to use cream of tartar, I prefer to use a little lemon juice. But overall, the value of adding these are not that great. It is more crucial to whip the egg white correctly.

Moisture In The Egg White
Too much moisture in the egg white can also destablise the foam. Water has a high density and will have the natural tendency to drain down the air-water border. As water begins to drain way, the 'membrane' will start to thin leading to the merging of bubbles or bubbles bursting. When making macarons, there are some recipes that calls for leaving the egg white to stand overnight in order to 'dry' the egg white. For chiffon cake, moisture from the egg white may not be that critical but some recipes do add a dash of corn-flour to help absorb the moisture.

Baking Temperature

The Chiffon Cake rises because the air bubbles swell under the action of heating.(air expands) In addition, as water content in the cake evaporates, the vapour also enlarges the bubbles. If the bubbles are not stable at this stage, they will break resulting in deflation. Hence the right baking temperature is vital. Heating the cake too fast will generate a rush of vapour that may stress out the air-water border.

Enough said - this is beginning to sound like a Science Lesson - but then, Baking Is Science.

Below is the recipe for the Blueberry Chiffon Cake. Overall a good recipe. Just watch out for the moisture content in the blueberries.

10. After baking, remove pan from oven, invert and cool completely. (preferably for 12 hours) before demolding.

Recipe :

MeringueEgg White 110g
Sugar 55g
Corn Starch 5g

Egg Yolk BaseEgg Yolk 40g
Water 12g
Grapeseed Oil 36g (or any other neutral oil e.g. canola oil)
Blueberry puree 50g
Lemon juice 6g
All purpose flour55g
Sugar 10g
Blueberry 30g (blueberry should be cut into very small pieces and dried with a kitchen towel. Best option would be dried Blueberry)

Method :
1. Heat oven using convection mode to 160C.
2. In a mixing bowl place egg yolk, blueberry puree, water, oil, lemon juice and sugar. Beat the mixture under well mixed and sugar is completely dissolved. (I do this by using a hand whip)
3. Sift flour into egg yolk mixture and mix well.
4. In a separate clean dry mixing bowl, whip egg white until foamy. Add sugar/corn starch mixture in 3 additions during whipping. Whip egg white until meringue is firm peaks.
5. Add 1/3 portion of the meringue into the egg yolk base. Use a spatula to blend egg white with egg yolk.
6.Add another 1/3 portion of the remaining meringue and blueberries into (5). Use spatula to fold egg white evenly with (5).
7. Add the remaining meringue into (6). Fold the egg white evenly with (6).
8. Pour (7) into a 17cm chiffon pan (do not oil the pan otherwise the batter will not rise).
9. Bake the cake at 160C for 30mins.