Learn how to make a white Genoise sponge without too much crust colour.
One of the reason why this type of sponge is preferred is because when you are making a layered cake, having that layer of crust contrast can make the cake unappealing and this sponge omits the step of having to trim the cake crust for the delicate white interior.
The common faults with making sponge cakes can be paramount if not done properly. The thing that makes a perfect sponge is the texture, look and mouthfeel. A good sponge cake should be light and fluffy with even air pockets throughout the sponge and no dense bit at the bottom or lumpy parts throughout the mixture when baked. The top should be fairly nice and even with a light to medium gold crust with no explosions.
Common ingredients in a basic sponge recipe
Some of the common main ingredients in a sponge cake are eggs, sugar and flour. To add some depth in flavour, vanilla and/or butter can be added.
How you incorporate the main ingredients together determine the end result for your sponge. The best way to learn to make a basic sponge is by understanding the purpose of each main ingredients.
A typical medium size eggs are usually 60 g in total weight including the shell: 10 g shell, 30 gram egg whites and 20 g egg yolks.
Without eggs, it will be impossible to make any cakes that are light and with a good flavour. Eggs is also the main contributor to expansion and airiness to the sponge as well as providing structure in your cake . Although, egg as a whole can aerate when agitated with a whisk in vigorous motion, if separated, they have a different phenomenon.
So, lets break down the eggs from its shell, separate the whites from the yolks.
Egg whites when separated from the yolks is capable of increasing up to 8 times its original volume when whisked. So, how does egg whites increase in volume just from whisking? Well, the answer to that question is: Protein. Egg whites is made up of 90% water and 10% protein. In fact, in this 10%, the egg white contain several different kind of proteins and one of the worth-knowing protein is the Ovalbumin Protein, which makes up to 54% of the entire 10% and it is this protein that contributes to the retention of air pockets and help the egg whites to increase in volume.
Ovalbumin contains many long chains of amino acids that curls up like a ball but uncurls when whisked or agitated. This uncurling allows the ovalbumin's amino acids to link on and wrap around the water molecules and air bubbles separately during the motion of whisking. Because the air bubbles are protected by these amino acid chains, the air bubbles are unable to come into contact with each other to form in to larger and larger pockets and ultimately burst. As the amino acids hold on to more and more air bubbles , the egg whites essentially expand in foams until it can no longer hold anymore air, and this foaming increases its volume.
Ever wonder why sometimes when you over whisked your egg whites, you will start to see a reverse result where the meringue starts to collapse and water releases from the mix? This is due to the atmosphere in the foamed egg whites being overcrowded and as it overcrowds, the amino acids that are wrapping around each air pockets will start to squeeze amongst each other and eventually burst, releasing some of the water.
One of the best explanation to this air pocket retention is by comparing it to pure water. When you whisk water vigorously with a whisk, you can see bubbles start to form, but as soon as you stop, the bubbles burst and dissipates almost instantly before your eyes. In egg whites as comparison, the same thing happens as with water when whisked. Air bubbles starts to form, but the difference is, because of the protein in the egg whites, the air bubble do not disappear instantly and remains. This is due to the ovalbumin's amino acid holding on to the air like its their teddy bear. If you leave the slightly whisked egg whites untouched for long, the air bubble will eventually dissipates over a much longer period time.
When whisking egg whites, it is essential to know when is enough and that certain point is often called the "Stiff Peak" where you are able to scoop the egg whites with a whisk and create a point at the end of the whisk without it unfolding and hold its shape well without falling back into the bowl.
Egg Yolks may seem like it does not contribute much after the lengthy benefits mentioned about egg whites but yolks itself plays a really important role as well. Egg yolks is known for its natural emulsifying properties called "Lecithin". Lecithin is important to bind two elements that do not normally want to come together: water and oil. This keeps the cake batter from separating. The addition of egg yolk helps to hold on to more water compared to batter that only contain egg whites, which ultimately yields a cake that is much more moist and less dense.
Another important thing about eggs as a whole as well is that it gives structure to the cake. When eggs are heated to certain temperature: 60°C- 65°C for egg whites, 65°C-70°C for egg yolks, the protein in the eggs will start to coagulate and turn into a solid mass, which help holds the cake in place without collapsing. Just picture frying egg, how the liquid egg starts to thicken and become solid as it hit the hot frying pan.
Like for anything else, sugar is sweet and so are all cakes. But don't let that seemingly small contribution that sugar gives fool you. Sugar does a lot more than just adding sweetness to your baked goods.
Sugar as a whole gives flavour and colour to your cake as it caramelises during baking. There is one other superpower sugar has as well that baking cakes can't do without, which is its hygroscopic nature. Sugar are attracted to water and tends to cling on to them whenever in contact with moisture. What this ultimately means is that sugar helps retain liquid in a cake better which then help keeps your baked goods nice and moist.
Another notable benefit of sugar is also its ability to stabilise the egg foams in the whisking egg whites. Because of the previously mentioned hygroscopic nature of sugar, as the sugar are incorporated in to the egg whites, it starts to draw into the water of the egg whites and begin to dissolve, which causes the water component of the egg whites to become thicker (like a sugar syrup). As the water content in the egg whites starts to thicken, it makes it harder for the air pocket to come into contact with one another as the thick sugar syrup are making it difficult to travel through. Just imagine swimming in a pool or water compared to swimming through a thick syrupy substance. This is also why egg whites whisked with sugar will start to become shinier as well compared to the ones that has no added sugar.
Although sugar is great for stability, too much can cause a reverse effect and disable the egg foam to increase making the meringue short with minimal amount of air. This can cause the sponge cake to not be able to expand as much or become dense.
Flour functions as a structure builder in almost all baked goods. The starch in the wheat flour contain a type of protein called "Gluten" when mixed with liquid. This gluten works together with the egg foam and liquid to help it expand, hold on to its structure and prevents it from collapsing during baking. Gluten is also what gives bread dough the extensibility and baked bread the chewiness.
In most delicate cake and sponges like this one, you only need a small amount of this gluten forming protein as to avoid the cake from being too tough but enough to give it that structure support. Therefore, cake flour or plain flour with a protein content under 8% is recommended.
Why not whisk the whole eggs together instead of separating them?
When making the sponge below, the egg whites are separated from its yolk and whisked to a thick consistency with the addition of sugar. The end product of whisked whites and sugar is called "meringue. When meringue are created, yolks are then added in to it before all the rest of the ingredients for this sponge.
So, the question here is, why not just whisk the whole eggs together in one go without separating them? ( You probably don't really mind the science that goes behind this but the curious mind always got the better of me).
Even though one yolk and whites may comes from the same egg, like siblings, sometimes they perform best on their own without the fighting amongst one another. Like egg whites, yolks is made up of water and protein but there is another component that yolks have as well that can inhibit the egg whites from foaming to its maximum capabilities, which are lipids, or in other word, fat. Even with a tiny morsel of fat present in egg whites can post a challenge for the egg whites to whip and aerate. This is because when fat is present, it creates a slippery atmosphere in the egg whites, making it difficult for the amino acids in the ovalbumin protein to hold on to the air pocket without slipping and sliding. This explains why sometimes you find that your egg whites foams up but do not increase in volume. There is no remedy if this happens and the best thing to do it discard it out and clean your bowl well before whisking a fresh batch of egg whites again.
Although you are still able to whisk eggs as a whole, but the volume you get in comparison to just whisking egg whites alone is phenomenal. Because in sponge cakes we want to achieve maximum aeration and volume of air for that light airy texture, often in this case, the eggs are separated and the egg whites are whisked instead of whole eggs.
Cream of tartar
Cream of tartar is a by-product acidic compound found commonly in barrels of wine which is then dried and pulverised into powder. Often time meringue recipe calls for adding in compound that are acidic such as cream of tartar, lemon juice or vinegar. This is because these acids acts as stabiliser for egg whites foams by introducing positively charged hydrogen ion into the negatively charged protein strands in egg whites. The acidic compound neutralises the egg whites and creates an atmosphere that slows down the denaturing (uncurling) of the amino acids in the egg whites protein allowing it to be whipped for longer without weeping (releasing water) as the egg white foams. This also explains why egg whites that has added acid in them can be left whisking and still hold on to its volume for a longer period of time compared to the ones without.
Baking in Water Bath is the key
Water bath refers to placing the tin with the cake batter in it over a hot steamy water whilst baking in the oven. The intention of a water bath is to create some form of steam in the oven which reduces the intensity of dry heat that are very common in domestic oven. Because of the mellowed down heat source in the oven, the air pocket that you work so hard to achieve do not expand too rapidly during baking which can often result in them bursting too soon or erupt on the surface of the sponge cake.
If you ever want to achieve a sponge cake without too much browning, water bath is the key.
In the method below for this basic sponge cake, the oven is set at a relatively lower temperature compared to the generic 160 - 180°C for cake baking. The baking temperature for this sponge is set at 150°C at the initial baking stage to give the sponge a kick at the start for a period of time then reduced to lower temperature for a slow and steady final baking.
Baking the cake on a water bath at a relatively low temperature also helps to prevent the cake from browning too much.
If you prefer a cake with that delicious brown crust, simply omit baking them in water bath and at a higher temperature than required in this recipe.
Equipment: 18 cm springform or removable base cake tin.
4 Egg Whites (approx. 120 g)
1 tsp. Cream of Tartar
100 g Caster Sugar
4 Egg Yolks (approx. 80 g)
120 g Cake Flour
2 g Salt
40 g Full/Whole Milk
30 g Melted Butter
¼ tsp. Vanilla Bean Paste
1. Line the 18 cm baking tin with parchment paper on the bottom. Do not grease the side of the pan as this can cause the cake to slide towards the centre during baking.
Pre heat the oven to 150 °C.
2. Place the room temperature egg whites into a stand mixer bowl fitted with a whisk attachment. Add in the cream of tartar and whisk over medium speed until the egg whites are foamy and there are not runny bits left. Gradually add in the sugar a little at a time. Once all the sugar has been added, increase the speed to high until the meringue reaches stiff peak or until the meringue looks shiny and when you scoop some of the meringue with the whisk, it holds its shape with a sharp point.
3. Add in the yolks at all once to the meringue and whisk until just combined without deflating too much of the air in the meringue.
Sift in the dry ingredients in 3 additions by gently folding it through the meringue with the help of a rubber spatula.
4. Mix the cooled melted butter and milk together in a bowl, place a few generous scoop of the sponge batter into it and gently mix to bring it to a similar consistency as the batter then add in the butter mixture back in to the batter and gently fold again until well incorporated.
Note: It is important that you do not over mix the batter too much as this can cause it to deflate and lose its volume.
5. Transfer the cake batter into the prepare cake tin and place it over a deep tray. Pour boiling hot water until 1/2 way into the tray. Carefully place the baking tray into the oven and bake the cake in the pre heated oven at 150°C for 15 minutes then reduce the temperature to 130°C and bake for a further 45 minutes or when gently touched, the top feels firm. Carefully remove the tray from the oven and remove the cake tin from the water bath.
6. Allow the sponge cake to fully cool. As it cools it will start to pull away from the side of the tin.
You can store the sponge in the freezer wrapped well in cling wrap for over 3 months.