All Natural Rainbow Cake

This Rainbow Cake features beautiful light and fluffy sponge cake layers that are naturally colored (no artificial colors or dyes), sandwiched with a vanilla Swiss meringue buttercream.

Why you'll love this recipe

This recipe is inspired from my Rainbow Mille Crepe Cake and yields a showstopping 6 layers of light and fluffy chiffon cake, all naturally colored (no artificial food colors or gel food coloring here!).

Using natural food powder colour instead of colored vegetable or fruit juice/liquid results in a more vibrantly coloured cake layers.

In addition, using a chiffon cake that is leavened with only eggs eliminates any unwanted colour changes by chemical interactions (with baking soda or baking powder).

Baking the cakes at a lower temperature helps to retain the natural colour more easily.

Special equipment you'll need

• 6" round cake pan: best if it is made of light coloured aluminum
  • in order to make this cake efficiently, it's best to have 3 x 6" round cake pans, however, you can make it with 2 pans -- you'll just have to make it in 3 batches rather than 2 batches
• electric stand mixer: for making the cakes, as well as the Swiss meringue buttercream
• mixing bowls: 6 bowls, one for each color
• silicone spatula(s): mini ones are great for mixing in the egg white meringue and egg yolks batter

Ingredients you'll need

For the rainbow cake colours:

• red: red yeast rice powder + red beet powder
• orange: red yeast powder + goldenberry powder
• yellow: goldenberry powder
• green: matcha powder
• blue: butterfly pea powder
• violet/purple: purple sweet potato powder (note: sweet potato powder can become a little lumpy in the cake batter, no matter how much you sift it -- this is due to the reconstitution of the powder)

You can find most of these powders online or at specialty health food stores.

For the cake:

• double batch of Perfect Swiss Roll Cake

For the vanilla Swiss meringue buttercream (SMBC):

• unsalted butter: at room temperature
• egg whites: about 3-4 large egg whites, at room temperature
• granulated sugar: to sweeten the buttercream
• vanilla extract: use a pure vanilla extract for the best flavour; you can also use vanilla bean paste as well

How to make the cake

Make the cake

Preheat oven to 325°F/163°C.

Prepare the 6" round cake pans by lining each pan with parchment paper.

Make a double batch of Perfect Swiss Roll Cake (chiffon cake).

Separate the egg whites from the egg yolks into 2 different bowls, while cold from the fridge.

Combine the egg yolks with 60g sugar and whisk together.

Add in the vegetable oil, milk, vanilla extract and whisk again.

Sift in the cake flour over top of the egg yolk mixture and fold gently to combine, until there are no lumps.

Weigh out the egg yolk batter.

Divide the egg yolk batter evenly into 6 different bowls.

Designate and add one colour to each bowl.

Mix the colour into the egg yolk batter evenly with a spoon or spatula. Set aside.

Add the egg whites to a stand mixer bowl fitted with whisk attachment, and whip until foamy.

Add in cream of tartar (or lemon juice) and continue to whip.

Once full of bubbles, gradually add in granulated sugar and increase mixer speed.

Whip until the egg white meringue reaches stiff peaks.

 

Weigh whipped the egg whites.

Divide the egg whites evenly into 6 different coloured egg yolk batter.

Fold the egg whites into the egg yolk batter, incorporating the coloured powder evenly.

Repeat with each colour.

Transfer one coloured cake batter into a cake pan, and repeat with however many pans you have.

Give the cake pan a few taps to release any trapped air bubbles.

Bake the cakes at 325F for 14-15 minutes, or until the surface springs back when pressed lightly.

Remove the cakes from the oven, give the pans a bang on the counter, and let cake cool in the pans for 5 minutes.

Transfer the cakes to a wire rack to cool completely.

Repeat the process with the next batch of cake batter and cake pans.

Once all the cakes are cooled, you can assemble.

Assemble and decorate

Place the violet/purple cake layer on a cake round, and onto a cake turntable.

Add about ¼ C of buttercream frosting and spread over the surface evenly with an offset spatula.

Add the blue layer and repeat, alternating cake layers with frosting.

To give the cake some structure since it's quite tall, it's best to add a dowel or long skewer before adding the final (red) layer. Trim off the excess with a sharp pair of scissors.

Once the red layer has been added, cover the entire cake with a crumb coat, or a thin layer of frosting.

Place cake into the fridge to set the frosting.

Spread another layer of buttercream frosting and decorate however you like.

Cover and store in the fridge until ready to serve.

Make the Swiss meringue buttercream

*Ensure that the butter is at room temperature before starting.*

In a stand mixer bowl, add in the egg whites and granulated sugar.

Heat the mixture over a double-boiler and whisk with a wire whisk until the mixture heats up to 165F.

The egg whites will become frothy and hot to the touch (and the sugar should be completely dissolved).

Remove the bowl and transfer to the stand mixer.

Attach the wire whisk and whip on high speed until full in volume, shiny and glossy.

Once the egg white meringue is at room temperature (feel the exterior of the stand mixer bowl), change the whisk to a paddle attachment.

On low-medium speed, add in pats of butter one at a time, until incorporated into the mixture.

Once all the butter has been added, add in the vanilla extract, increase the speed and whip until the buttercream is light and fluffy.

Troubleshooting Swiss meringue buttercream

Buttercream not coming together

Temperature plays an important role in making buttercream.

By playing with the temperature -- chilling it or heating the buttercream, it will come together.

Curdled / grainy / soupy buttercream

If the buttercream appears curdled, it means the butter was too cold, or liquid was added too soon (eg. vanilla extract).

Remove about ¼ C of buttercream, place into a bowl and heat in a microwave until completely melted.

Drizzle the melted buttercream back into the mixture and continue to whip -- it should homogenize and come together.

If it appears soupy, then the butter could be too warm and melty -- pop the entire mixture into the fridge for 5-10 minutes to help it firm up.

Alternative: use a blow dryer on hot and heat one section of the stand mixer bowl until it is hot to the touch. This will also melt some of the butter and help it homogenize.

Tip: If in doubt, just keep whipping on high speed, it will eventually come together.

Buttercream not sweet enough

If the buttercream is not sweet enough, add sifted powdered sugar to your desired sweetness.

Buttercream too runny

Add a little powdered sugar to help stiffen it up.

How to serve & store

You can serve the cake right from the fridge, or leave it at room temperature for about 15 minutes if you prefer a softer buttercream.

Store the cake in a covered container in the fridge for up to 3 days.

To freeze the cake, slice into portions and wrap with plastic wrap or place in between layers of parchment paper in a freezer-safe container.

Freeze the cake for up to 3 months.

Expert tips & troubleshooting

Can I make the cakes ahead of time?

Yes, you can make the cakes 1-2 days beforehand, wrap each layer up with plastic wrap and place into a freezer bag.

Keep at room temperature for up to 2 days.

You can freeze the cake layers for up to 1 month.

Defrost the cake layers overnight in the fridge the day before you plan to decorate.

Cake is not even

If the cake is not even, you can use a sharp serrated knife to level the cake.

Cake has browning on the surface and/or edges

This can sometimes happen, even when baking at a low temperature.

Note: If the tops are browning too quickly, cover the cakes with aluminum foil.

To remove the brown parts, use a microplane shaver and gently "shave" off the brown bits.

Use a pastry brush to lightly brush off the cake crumbs.

Buttercream curdled

See troubleshooting tips under Swiss meringue buttercream.

Substitutions

Colors:

If you don't want to use natural food powder colors, you can use gel paste food coloring.

Start with a toothpick dabbed into each color and work it into the egg yolk batter.

Adjust by adding the amount of color to your preference.

Note: gel colors are very concentrated, so a little bit goes a long way.

Cake:

If you don't want to make cake from scratch, you can also use a boxed white cake mix.

Frosting:

Don't want regular vanilla frosting?

Switch it up with a cream cheese frosting instead.

Other cake recipes you may like

Be sure to check out these recipes:

All-Natural Rainbow Mille Crepe Cake

Matcha Jasmine Cake with Yuzu Curd

Taro Coconut Cake

Black Forest Cake

Funfetti Cake

Strawberry Whipped Cream Cake

Let me know if you try out this recipe -- tag me on Instagram @siftandsimmer or leave me a comment/rating below!