Finally, I am getting everything right on how to make the Japanese sponge cake after many attempts.

The cake is bouncy like a sponge, with the soft and delicate texture resemble cotton when you tear it apart.

I also add the cake batter to the dough of the chocolate Japanese milk bread. Here is the result- my delectable bread-cake that I missed so much after the nearby bakery decided to stop producing it.

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How to make Japanese sponge cake in twenty minutes

This article is all about how to make the Japanese sponge cake. Please refer to this article to find out how to make the Japanese milk buns that are incredibly soft.

The process of making the Japanese cotton sponge cake is similar to most of the sponge cake recipes. Nevertheless, there are some fine details which I will explain in detail in the following sections.

1. Measure the flour and butter correctly

The importance of sieving the flour

Measure 100g of plain flour and sieve at least once. What I mean by plain flour is any wheat flour that is label as cake flour or all-purpose flour. The percentage of gluten in these type of flours is relatively low, about eight to ten percent, which is ideal for making sponge cakes.

I sieve the flour not because it is dirty. The flour that I get locally are very clean, but I want to ensure that it is free from any lumps and large particles. The fineness of the flour is critical to get the cottony texture. If you happen to get any superfine cake flour, go for it. It will significantly improve the texture of the cake. Since I have not been able to purchase it this time, I have to sieve the flour to make sure the cake will turn out well.

Use melted butter to mix with the flour

Place 75g of unsalted butter in a pan/pot over low heat until it melts. You can melt the butter in the microwave oven by using low heat for a minute. Keep an eye to the butter and do not brown it as it will alter the flavor and smell of the butter.

You may want to substitute the melted butter with corn oil. However, a sponge cake made with good quality butter has a better flavor.

Add the flour to the melted butter after it is cooled. We do not want to add the flour to the hot butter to avoid the flour being cooked at this time. We are not here to make choux pastry!

Do not worry if the flour and the butter forms a sticky mass at this point of time. It will turn into a smooth batter after adding milk and the egg yolks subsequently.

Note: This is not a gluten-free formula. I have not tried to make a sponge cake with any gluten-free recipe so far.

2. Add the milk

Add 60ml (4 tablespoons) of milk to the flour-butter mixture. You may pour all the milk into the mixture or add in batches. It will not make any difference to the result.

The milk will dilute the flour-butter mixture to form a thick paste.

3. Separate the egg yokes from the egg whites carefully

We need to add the egg yolks to the above flour-butter-milk paste to form the batter.

So far the process is relatively straight forward. There is quite easy and does not involve much technique. However, please pay attention when you separate the egg yolks from the white. It can be the make or break step for this recipe.

Do not even let a trace of egg yolks contaminate the egg whites. We need pure egg whites to prepare meringue, and it has to be free from oil to be successful. Egg yolks are oily, and that is why it has to be very careful not to break the yolks.

Here are my recommended steps:

• Use a clean stainless steel bowl to keep the egg whites. Wipe the bowl with paper towels to make sure that it is free of oil. The bowl must be large enough as we will use it to beat up the egg whites to form the meringue.
• Use the egg yolk separator to remove the egg white from the yolk. I always crack the egg in a separate bowl to make sure any broken eggs will not contaminate the bulk of the whites.
• It is not possible to separate all the whites from the yolks. However, there should not be even a trace of yolk in the white as it will hinder the expansion while making the meringue.

4. Making the batter

Lightly beat the egg yolks and add to the flour-butter-milk mixture.  Again I have tried to add the egg yolks in batches to the mixture, but it makes no difference compare to pouring all the yolks at one go.

The egg yolks will dilute the paste further into a batter. It is at this time that you need to mix it thoroughly. I mean to mix it, not to beat it as beating will create bubbles that are not a welcome inclusion to the cotton-like texture.

Mix it in one direction until it is free from any visible lumps. The final batter should have a very smooth texture.

Once you have done that, you have won half of the battle. Let’s move on to prepare the meringue.

5. Beat the egg whites until it forms stiff peaks

The egg white should be at room temperature while making the meringue. Remove the eggs from the refrigerator and wait for it to return to the room temperature before cracking them.

Beat the egg whites with a hand-held mixer at low speed. If the room temperature is too low during winter, place the bowl of egg whites on a hot water bath. Warm egg whites can trap more air in its structure and expand its volume rapidly during the beating process.

• Add 80g of castor sugar or fine sugar into the egg white after fifteen seconds of beating.
• Continue beating the egg whites until the volume triple. The egg white will change gradually from transparent to pure white, and become thicker.
• Eventually, the egg whites become so thick that when you switch off the electric beater and turn it upside down, the egg white that sticks onto the beater blade will become so stiff that it will firmly stand without drooping. Beat the egg whites until it can form a stiff peak.

Nevertheless, some bakers prefer to beat the egg whites to form a soft peak, which means that the peak will droop a little when you overturn the beater blade.

How to maintain the best volume for the meringue

If the meringue forms only until the stage of the soft peak, it will lose volume rather quickly while you start to fold since it is less stable. In contrary, meringue that forms stiff peak stage is firmer and need more folding until it can incorporate uniformly with the batter. The longer you fold, the batter will deflate more.

My preference is first to beat it until it forms a soft peak, then beat further by stopping every twenty seconds to check if it achieves the stage of stiff peak. I do not want to overbeat it because the meringue is hard to combine with the batter once it becomes too stiff.

I will dilute the batter with a quarter of the meringue so that it is easier to mix, then add the diluted batter back to the bulk of the meringue. Fold the meringue into the batter slowly until it is almost homogenous.

The batter will deflate beyond the optimum level if you fold the meringue until the batter is homogenous.

Then I will pour the cake mix into the cake pan. The pouring action will finish up the last bit of mixing which will eventually produce a homogenous cake mix in the pan.

6. Line the cake pan with baking paper

Line the cake pan with a large piece of baking paper enough to cover the sides of the square cake pan. Brush the paper with some melted butter.

Since I am using a cake pan with a detachable base, I have to wrap the exterior of the pan with aluminum foil to avoid the water from the water bath from seeping into the pan.

After pouring the cake mix into the pan, you will notice there will be some bubbles on the surface. These bubbles will create little craters on the surface if you do not get rid of them. You can do this by:

• Gently tap the cake pan a few times to break the large bubbles.
• Use a bamboo skewer or toothpick to break the smaller bubbles.

7. Baking at the right temperature

Place the cake in the hot water bath. Once the oven is heated, bake at 150°C/300°F for sixty minutes.

But it may not be right sometimes!

The recommended temperature and baking time is one of the most unreliable measurements in any recipes for cakes. Most of the ovens do not have a very accurate temperature indicator. The heat distribution and the size of the oven is another factor that affects the final result.

My suggestion is to take a quick look at the cake after baking for forty minutes. If the cake has already expanded, then it should be fine. Otherwise, increase the temperature by 10°C to make sure the air trapped in the batter expands and push up the cake.

When the cake is nearly done, you can open the oven door more often without worrying the sudden drop of temperature will cause the cake to deflate. Check the color of the cake. The actual baking time will depend on the color of the cake. You need to check. It is not possible to set the temperature precisely each time unless the oven has a digital control panel.

8. Do not cut the cake immediately after baking

Remove the cake from the oven and water bath and let it cools on the table for fifteen minutes. The cake will shrink a little and detached from the sides of the pan.

Overturn it onto a wire rack and remove the paper. Then, place a cake board on it and revert the cake again. Now you have Japanese sponge cake ready to cut and serve.

Additional information – May 2020

I have just revisited this recipe as some of the readers were unable to produce the same result as mine while following the recipe diligently. There are two commonly happened problems that I want to address.
– The cake is undercooked at the bottom. 
– The cake is dense. 

1. Why is the sponge cake undercooked at the bottom? 
The cake is baked in a water bath. The purpose of the water bath is to provide a slow and even heat, protecting the delicate sponge texture. The cake will rise slowly and evenly with no rapid expansion, and therefore achieve a smooth and cottony texture. 

However, the water at the lower part of the cake brings down the temperature, causing the upper part to expand faster than the lower part, resulting in the bottom becomes denser than the top.

To solve this problem, I have made two adjustments:
– First, increase the temperature to 160 °C/320°F.
– Put the cake on the lowest rack of the oven. The bottom of the cake will heat up efficiently now and rise at the same speed as the top, and will not cause the formation of a dense layer. 

The water bath will still function to ensure sufficient moisture in the oven, forming a flat top surface without crack, and moist texture. 

The lowest rack of my oven is just one inch above the bottom heating element. You may need even higher than 160°C if it is further away from the heating element. You have to forgo the water bath if it still doesn’t work. There are no two ovens that behave the same. The cake will become dryer without a water bath, though.

The most common reason when the sponge cake is still uncooked after baking one hour is due to low temperature. The distance between the baking rack and the heating element makes all the difference. You know your oven best!

2. Why is my sponge cake denser than what is shown in this post? 
In my opinion, the main reason is overmixing while folding in the meringue. If I mix until the meringue is disappeared, the cake will deflate too much, resulting in a dense texture. 

It is better to fold in the meringue gently and stop when there are still traces of meringue scattered randomly in the batter. Pouring the batter into the cake pan slowly from a high position will give the batter a final mix naturally. 

Also, the meringue should be beaten until you can make a stiff peak when leaving up your spatula. Otherwise, it will collapse rapidly during mixing and folding and resulting in a dense cake.

Take a look at the two images below. 

Variation: How to make Japanese sponge “cake-bread”

I also combine this recipe with the Japanese milk bread published in this blog to create a cake-bread loaf. You can refer to the bread recipe article to make the bread. I have added a teaspoon of cocoa powder to change the bread to a chocolate color.

To do this. Place a small dough of the bread into a loaf pan. Pour the sponge cake mix on the dough after it doubles in size. Bake as the same temperature and duration in the sponge cake recipe.