Scaling recipes and baking tall layers requires advanced baking skills.
You need to know baker's percentages and you need to know how to find the area of a circle. Since the height of the pans are different, in this case you need to find the volume of a cylinder.
Your recipe must be in weight not volume, and preferably in metric weight because metric weight is far more accurate. If your recipe is written in volume it cannot be scaled.
Sponge cake is not a cake for the novice baker for a number of reasons.
Achieving rise is easy. Maintaining that rise are lessons in practice and experience. The layers in the cake pictured are not 4". And they are not 4" for very good reason: keeping a sponge cake from collapsing is no easy feat.
The French version of the sponge is leavened by nothing but egg whites. All egg white leavened cakes are notorious for deflating and shriveling. They deflate while baking. They deflate while cooling. They deflate for the pure sake of deflating. If your recipe is the Italian version, the genoise, you have a better chance, but the Italians do not like to be out done by the French, so their version is also a persnickety little cake that will deflate for no explicable reason.
Given the sponge cake's propensity to deflate and shrivel, it's not advisable to attempt to bake one twice the height of a standard cake.
This event is your event. This is your wedding. The days leading up to your wedding date will be filled with work and stress. Do you really want to pile on the stress of producing your own wedding cake, and of the sort that's given to collapse?
There's also issues unique to naked cakes. Naked cakes need to be sturdy since they do not have buttercream to support and camouflage the sides. A soft cake will collapse at the sides.
With so little buttercream, naked cakes dry out very quickly. So your cake recipe should be a very moist one.
Since naked cakes dry out very quickly, your baking schedule and storage prior to event is critical. You cannot use the same bake and storage schedule as a cake that will covered in icing. You cannot bake the layers three days in advance and store them in the refrigerator. By the time it's decorated and served the cake will be as dry as the desert.
To mitigate drying out while on display, naked cakes are normally assembled at the very last minute to minimize the time the uncovered cake is exposed to air.
It's not just the bake and assemble schedule that will effect the cake quality. The type of cake is a component as well. Sponge is dry. It's the nature of the beast. All those egg whites give a sponge cake it's characteristic dryness. All those sponge cakes you eaten at other people's events and from bakeries have been moistened with simple syrup. Simple syrup is added to each layer during the decorating process. Too much simple syrup will make the cake soggy and the cake may collapse. Too little simple syrup, then the cake is dry.
Naked cakes are not glued it together with icing; so you must support the tiers properly for stability.
Baking tall layers have their own issues as well. Given the volume of batter, the center of the cake will take a lot longer to bake. Cakes 3" and taller require a heating core. A heating core will leave a hole. The size of the whole depends on the type of core you use. Some bakers improvise and use flower nails as heating cores. For a 6" cake, 1 flower nail; 8" cake use 2 flower nails. For a 10" cake use an actual heating core. A flower nail won't radiate enough heat in a cake 9" or larger. If you do not use a heating core, the center will bake much slower than the rest of the cake. The cake will be dry all over except the very center.
For 3" and taller cakes you must reduce the temperature and increase the bake time. The only way to know how much you need to reduce the temperature and increase the bake time is to bake the layers and find out for yourself what the adjustments should be. You can scale a recipe for batter quantity, but there's no way to "scale" temperature and time accordingly.
Given the increased bake time it is best to use a pan made of uncoated metal. Non-stick pans conduct way too much heat. If you purchased Fat Daddio pans you will need to drastically reduce the temperature. The anodized aluminum conducts way too much heat. I am not a fan of non-stick and Fat Daddio--they all create a very brown dry crust to begin with. Extended bake times mean an almost burnt looking cake with a dry chewy crust.
If after all I stated, you want to proceed here's how to scale the recipe.
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Since the pan depths are different, you have to calculate for volume rather than area. Keep in mind that there's some unknowns--mainly the volume of batter the original recipe produces, and the rise and shrinkage after cooling. Even though it calls for a 2" deep pan, the cake after baking and cooling may not be 2" high. Since the volume of batter itself is an unknown the calculations are not specific to the batter. Rather the calculation addresses maximum volume capacity of pans.
The last unknown is the expansion of the batter. If the egg whites are beaten separately and fold in, the batter will expand considerably. The amount of expansion depends on the amount of air that has been beaten into the egg whites. If the egg whites are under or over beaten, there will be less than ideal expansion. In that case. even if you fill the pans with the appropriate amount of batter, the cakes will not rise to maximum height.
Adjust the original recipe for a single pan:
- Calculate the baker's percentages of each ingredient in the recipe. While US weight will work, it's far better to use metric weight when scaling. If your recipe is in volume (cups, teaspoons) it cannot be scaled.
- Since your recipe yield is two 8" layers, after you calculate the baker's percentages, reduced it by 50%. This reduced amount will be the basis on which you make the batter calculations. I'll call this the "adjusted original recipe"
Calculate the area and volume of the original 8" pan
- Find the volume of the original cake pan. Volume = pi x radius² x height
8/2= 4
4 x 4 = 16
16 x 3.14 = 50.24
50.25 x 2 = 100.48 (round down 100)
The original recipe will yield enough batter for a pan with a volume capacity of 100.
- Find the volume of the 10" cake pan.
10/2 = 5
5 x 5 = 25
25 x 3.14 = 78.5
78.5 x 4 = 314
The volume capability of the 10" x 4" pan is 314
- Calculate the difference in volume between the original 8" pan and the 10" pan. Divide the larger size pan into the small size pan
314/100 = 3.14.
The original recipe need to be increased by 3.14.
- Using the baker's percentages for each individual ingredient, multiple by 3.14.
Repeat calculations for 6" x 4" and 8" x 4" pans
NOTE: when scaling for pans of same height, do not factor in pan heights. Just calculate area. Area = pi x radius² .
Keep in mind, The calculations are for maximum capacity of the pan. Cake pans are not filled maximum capacity to allow room for the batter to rise. The assumption is the original recipe has been scaled to allow for the appropriate rise. The conversations are based on the rise of the original recipe.