Genoise Sponge

The genoise (pronounced gen-wahz) is possibly the most elegant of the air-leavened sponges, a type of cake that relies solely on air to rise. Essential for gossamer layer cakes and all matters of fine pâtissèrie, the genoise has a slightly richer and denser crumb than some of its air-leavened counterparts, like chiffon or angel food cake, making it light enough to disappear on the tongue, but stable enough to be soaked in syrup and act as a building block in multi-layered cakes. 

What is Genoise?

In its simplest form, genoise has just three ingredients: eggs, sugar, and flour. It may also be enriched with butter in a simple ratio of 1:2:2:4 (butter, sugar, flour, eggs by weight). Whilst you could seek out an ultra low-protein flour, you can approximate this by using a mixture of all-purpose flour and cornstarch in a 70:30 ratio. By reducing the available protein in the flour, we limit gluten development and will be rewarded with an ultra tender cake with a velvety crumb. 

I’ve always considered the ever-popular chiffon as the genoise’s American counterpart. The two cakes share many similar attributes like a lighter-than-air texture, but the methods and ratio of ingredients differ. Both cakes rise in the same way: air bubbles are trapped in the batter and, when baked, the bubbles expand. It’s the manner of how the air is introduced that differs. For chiffon cakes, egg whites are whipped into a meringue and folded into the base, whereas genoise relies on whipping whole eggs to ribbon stage―the voluminous state in which the egg transforms into a foam that has enough body to hold its own weight and runs off the beaters in glossy ribbons when lifted.

The ultimate challenge of the genoise sponge is creating and maintaining air bubbles. If this structure is damaged during the mixing process, you can get into trouble and will likely end up with an uneven crumb, erratic air pockets or, even worse, a sponge that is completely flat and rubbery. Being the fussy cake that it is, there are hazards at each stage. Fortunately, each one of these threats can be neutralized with good technique.

Getting the Perfect Foam for Genoise

The key to a great genoise lies in the foam formed with the eggs. You may be familiar with the extraordinary ability of egg whites to capture air bubbles, which, when fully whisked, can increase by six to eight times their original volume, allowing for fluffy pie toppings and airy meringues.  But just because whole eggs can't expand as much, it doesn't mean they don't offer other significant benefits when beaten. Compared to egg whites, which are 90% water and 10% protein, whole eggs are 74% water, 13% protein, and 9.5% fat. Whisking whole eggs yields a shiny, flexible foam that can expand up to five times their original volume. This produces a foam that isn't as stiff as egg whites, but provides a stable and flavorful backbone to genoise, as well as other desserts like flourless chocolate cake. Whole eggs will effectively trap less air than egg whites since there is less protein available to make the protein mesh responsible for this aerated structure, so a whole egg foam will result in a richer crumb because of its fat. Plus, the lecithin in the yolk, which acts as a powerful emulsifier, stabilizes the foam and makes it virtually impossible to over-whisk.

Genoise is traditionally made by whisking eggs in a bowl over simmering water until around 149°F (65°C). This process of warming the mixture allows the foam to form more quickly since heat encourages the egg proteins to denature (meaning they unfold and create bonds with one another, trapping air in the network). I’ve found, though, that the effort required does not make a difference in the genoise’s final crumb. Instead, I recommend using either room temperature eggs or ones straight from the fridge (which just take longer to whip up) for the sake of expediency.

Whisking whole eggs successfully, though, isn't as simple as simply beating them as one would egg whites. While it is possible to whip your whole eggs into a frenzy and achieve an extremely fluffed-up mass in a matter of minutes, the resulting foam will have a chunky texture with lots of visible, irregularly sized bubbles. In theory it will have reached the desired ribbon stage, but folding the flour into this erratically-structured egg foam is difficult. You run the risk of deflation, and are likely to see those defects carry over into your finished crumb. 

To produce a superior genoise, I like to instead mix the eggs in three stages. First, I whip the eggs at high speed to fully aerate them. After this initial step, I lower the mixing speed in two stages as I continue to whip the eggs. As they whip, the large unstable bubbles are split into smaller and smaller, more stable bubbles that are no longer visible. Taking the time to do so yields an incredibly smooth, pourable, and shiny foam. As a result, your egg foam will be easier to work with, and less at risk of collapsing during the folding stage, and your cake will have a more even expansion in the oven and an overall better crumb.

The Folding Technique

Incorporating the dry ingredients is a make-or-break moment for the genoise sponge and good folding technique is essential to maintain all those hard-earned air bubbles. Folding is the action used to incorporate flour, which consists of methodically and gently cutting through the egg foam while adding flour in several parts. I like to add the well-sifted flour in thirds and to use a capital ‘D’ motion, slicing through the centre of the foam and using the edge of the bowl to guide the spatula. Once a fold is complete, I turn the bowl 45 degrees and repeat. Poor folding technique is often the culprit in heavy or flat sponge cakes. Moving your egg foam to an extra-wide bowl (compared to a stand mixer bowl) and increasing the surface area can be really helpful in promoting good technique since you don’t have to dig deeply into the mixture to fold it, thus breaking less bubbles each time you fold.

The Best Way to Incorporate the Butter

Due to the radically different densities of the airy egg foam and heavy butter, it can be a challenge to incorporate the fat. If you add it all at once, it will sink to the bottom of the bowl and you will likely overmix the batter in an attempt to incorporate it, leading to deflation. To make the process seamless, I rely on what's called a liaison batter—made by whisking a bit of the flour-egg mixture into the melted butter, which results in a batter with a more similar density to the flour-egg mixture. Think of it like tempering the mixture, like you would eggs for custard. The liaison batter combines seamlessly with the foam, radically reducing the risk of overmixing and deflation.

Eliminating Large Air Bubbles

Now despite your best efforts to minimize unstable air pockets during the mixing stage, the folding process will likely introduce additional volatile pockets of air. The solution may seem a little unsophisticated, but it works. Lift your filled cake pan about eight inches above your kitchen counter and drop it. Dropping the cake helps burst any large, unstable air bubbles. 

You’ll perform the same action post-baking to prevent the delicate sponge from shrinking inwards as it cools. In The Science of Cooking, physicist Peter Barham theorizes that cakes collapse because all of the steam that helped expand the air bubbles to make the cake rise condenses during cooling, and new air cannot flow into the cake to replace it. As a result, the cake, lacking enough structure to fully resist this contracting force, shrinks. According to Barham, dropping the cake “passes a shock through the bubble walls and allows some of them to break, converting the cake from a closed to an open cell structure,” thus allowing air to make its way back in and prevent shrinking.

Once cooled, a genoise sponge is a versatile friend in the pastry kitchen. It can be soaked with a simple syrup then sandwiched with strawberries and cream for an elegant tea time slice, layered with mousses, jams, or creams for patisserie-style layer cakes, or formed into rolled cakes when baked in a sheet (this can be used in frozen layer cakes, like baked Alaska, since the aerated structure will never allow the cake to freeze rock hard). Similar to a ladyfinger, it’s also robust enough to soak up liquid in a tiramisu or trifle, both of which are perfect make-ahead dinner party desserts.