Notes on how to solve chiffon cake problems: How to reduce the shrinkage? Why does my cake shrunken in the middle?

I finally successfully baked a cake without shrinkage problem. So, where's the trick? What causes it to shrink? I'm writing this blog post because I notice that not many have written on this matter. Even if they do, the solutions did not solve my problem. So, lucky for you (if you are facing something like what I did previously), you are going to say farewell forever to your unsuccessful chiffon cake base.

Cake with a hole at the bottom/Cake sunken in the middle 

For your information, the above cake is baked by me. Horrible attempt. It's a total failure. I will let you know the few method that I thought will work. Unfortunately, they have proven to be untrue.

Attempt 1# 
Cake size: 7 inches (4 eggs chiffon cake base recipe)
Bake: 160 degrees Celsius in 55 minutes
Position: Middle rack
Rationale: I'm baking the cake at a super low temperature in a longer time period.
Result: Fail 

Attempt 2# 
Cake size: 7 inches (4 eggs chiffon cake base recipe)
Bake: 160 degrees Celsius in 80 minutes
Position: Middle rack
Rationale: I thought the time could be not long enough. Thus, I extended the baking time.
Result: Fail 

Attempt 3# 
Cake size: 7 inches (4 eggs chiffon cake base recipe)
Bake: 170 degrees Celsius in 80 minutes
Position: Middle rack
Rationale: The picture above shows what happen to my original flavour chiffon cake base. I thought the temperature is not high enough which results in unbaked cake. So, I increase the temperature instead this time, keeping the time duration similar. As a result, the cake has a really crusty dry surface all around it.
Result: Fail 

Attempt 4# 
Cake size: 7 inches (4 eggs chiffon cake base recipe)
Bake: 140 degrees Celsius (20 minutes), 150 degrees Celsius (25 minutes), 160 degrees Celsius (5 minutes)
Position: Bottom rack 
Rationale: I changed the position of the rack to the bottom instead of the middle. I lowered the temperature further down but vary them so that the surface of the cake bake nicer.
Result: Successful 

Poor me. I had to try so many times before I could get a beautiful cake like below:

The trick to get really beautiful and non-middle-sunken cake is to place your cake to be baked at the bottom rack. I was told to bake at the middle rack all these while. I was not aware of some recipes which state that you need to bake your cake at the bottom rack. I did not know that it was a crucial point to determine the final outcome of your cake. Ha -! 

Here's some theories and rationales that I could think of:

Disclaimer: I'm just a person who is passionate in baking. I don't have any certificates in culinary art. I just love to read, watch videos and experiment by myself: 

Why is your cake sunk in the middle? 

I have read so many articles and watched so many videos. Some said it is because of high temperature and some said low. I don't think both of them are the answers. It is simply because your cake still contains water in the middle however the overall surface of the cake has fully baked. Thus, when you remove your cake from the oven when there's still water in it, you will end up having a sunken middle cake. The weight of the cake itself is too heavy in the middle and when you overturn your cake to cool on the rack, the weight causes the "hole". 

How do I know it is due to water trapped in the cake?

I experimented a few types of cakes and what I can deduce is: when there's still water in the cake, your cake is 99% likely to fail (didn't come out perfect as you are hoping it to be). I tried baking Hokkaido cupcakes which emphasize a lot on getting the cake baked dry. Otherwise, your cupcakes will shrink so quickly that you cannot even do anything to save them. Never ever take the cake out when you know there is still water in it. Let them be in the oven and bake a little while longer until they are fully dry. 

How to know whether there is or isn't water in the cake?

Putting a toothpick or needle into the middle of the cake to test whether it comes out clean to prove whether a cake is cooked or not - I think this method is not reliable at all. It failed me so many times. I never bothered to do this anymore. Firstly, you need to be familiar with your oven temperature and time settings. For every different type of cake, you need to roughly know how long it takes to bake. Most recipes will come with the suggested time and temperature. However, it is still essential for you to have a grasp based on your understanding of your own oven. 

Only open the oven door to check when the cakes are almost time's up. Do not ever open the oven door too early otherwise, you will get a shrunken cake in the oven itself. There is nothing you can do about it. Just enjoy a shorter cake and that's it. I've tried this before and trust me, you do not want this. The cake will shrink so much so that it goes back to the original height of the batter before you put into the oven. Argh - Reason - the cold air from outside the oven enters the oven before the cake is fully developed and baked. 

So, to check whether there is still water or not - simply place your hand on top of the cake and give it a light force press. If you can still hear a noise that sounds "sha-sha" or "zzz zzz".. it means there is still water inside. You will know what kind of sound this is if you have tried doing this before. Otherwise, it's really difficult to explain/describe. This method works almost all the times. Forget about the toothpick and needle. Take out your cake to chill when you don't hear any sound when you press the cake. You're likely to get a 99% perfectly baked cake (don't count those with excessive high temperature till the cake is burnt on top). 

I guess the 3 questions above are the most important ones to answer why your cake shrink. 

Before this, I doubt if it is due to the lining of the paper. Some even told me it is due to baking containers. I was using only the normal baking containers with no removable bottom lids. I tried again and again. Finally, I can come to the conclusion to tell you - it has nothing to do with the baking containers. It has nothing to do with the lining too. If you are concerned with the question - why does my cake shrink? 

What are the differences when you line and don't line the baking containers for chiffon cake base? 
When you line the baking container with non-greased paper at the bottom only:
It's easy for you to remove the cake out later. You just need to get a knife and loosen the cake on the sides. Then, overturn the cake on a rack. Even without applying oil on the paper, your cake can still get the cake out from the mold perfectly.

When you line the baking container with greased paper at the bottom only:
Use the similar method of how to get the cake out from the mold as explained above. You will have lesser cake stain on the paper. So, you will get more cake to eat.

When you line the baking container with greased paper at the bottom and sides: 
You will get clean cake with lesser stain on the paper. However, your cake will not grow that tall as compared to non-greased container.

When you line the baking container with non-greased paper at the bottom and sides: 
More cake will stain on the paper. Your cake will grow slightly taller compared to greased container.

I think I've answered most of the questions pertinent to this topic. Hopefully you bakers outside there don't get that miserable anymore - you will be able to get beautiful cakes like I do, finally.Ha ha ha ha -

The final tip for chiffon cake base: 

Always allow your cake to bake longer in a lower temperature. Also, do not forget to place your cake at the bottom rack. 

Oven Fan

I'm not sure with the factor of oven fan switched on or off. I noticed that buns and cake tend to bake better when the fan is switched off. So, yeah - don't switch on the oven fan while you're baking cakes and buns. For buns, when I switched on the oven fan, they tend to "colour run". Some buns don't turn out very evenly baked.