Baking a Rainbow Cake – Frequently Asked Questions

How to bake a simple Rainbow Cake - recipe at kerrycooks.com

 Hi guys! It’s been eighteen months since I first made my simple Rainbow Cake here on Kerry Cooks, and in that time, Rainbow Cake’s have become even more crazily popular! BBC Good Food even featured one in their magazine (although it’s apparently not nearly as reliable as mine, judging by the reviews!).

If you’re thinking of making one, rest assured that Rainbow Cake can be easy and stress free. My recipe is a simple Victoria Sponge recipe that’s been adapted for bigger quantities. Once made, the batter is divided into six and the colouring added to give the bright rainbow layers. Dozens of people have made it with great success – check out the comments!

What type of food colouring should I use?

It’s really important that you use highly concentrated food colourings for this cake. These are normally called gel or paste colours. If you use an old fashioned liquid food colouring, the cake will taste horrible, and the colours will be insipid and weak (NOT a vivid rainbow!). The brands to go for are –

Yes – Sugarflair, Americolor, Wilton,

No – Dr Oetker (gel), Silver spoon (gel), any liquid colours whatsoever

As mentioned in the recipe post, I normally stick to Sugarflair for every colour except purple (Sugarflair’s grape violet is too dull in my opinion) – I use Americolor’s Electric Purple instead.

If you have a specialist baking supplies shop nearby, you should be able to find gel colours for between £2.50 and £3 per pot. Failing that, you can buy sets of gel colours specifically for Rainbow Cake’s from eBay, and other online shops too –  I recently bought some Americolor’s from Fair Cake.

I wrote a whole post on the subject of colouring cake sponge here.

Baking a Rainbow Cake - Frequently Asked Questions

Could I add other flavourings to my Rainbow Cake?

Yes! You could add a flavouring extract such as strawberry, almond, lemon, or even something more exotic like bubblegum.

What size cake tins did you use?

I used 6 inch disposable ‘flan cases’ to bake my cakes, which I bought from Wilkinson’s (UK). 6 inch tins is why my Rainbow Cake was so very tall! Depending on how tall you’d like your cake to be, 6, 7, or 8  disposable tins would work great – you’d just get either a taller or less tall cake. If you want a cake that’s bigger than 8 inches, you’ll need to scale up the recipe.

Lots of supermarkets and pound shops sell disposable cake tins too, so stock up whenever you see them. I even re-use mine, with a quick rinse and turn in the dishwasher.

Baking a Rainbow Cake - Frequently Asked Questions

How did you prep the tin foil tins before using?

The great things about disposable tins is that cakes seem to come out of them really easily. I simply prep by brushing melted butter around the bottom and sides of the tin (alternatively, you could use a cake release product). If your cake does get stuck, never fear, simply cut the tin foil sides of the tins at about every inch, and then flatten the sides – you should then be able to get a palette knife under the cake to loosen it.

How high will my layers rise?

The layers should be between 1 and 2 cm high, depending on what size tin you use. If your cakes don’t seem to have risen, troubleshoot by checking your self-raising flour – is it well within date? You should also try to get the cakes into the oven as soon as possible once the flour is added to the batter – not easy given that you’re dividing it into six and adding the colours, but work as quickly as you can.

Can you make the layers ahead?

Yes! In fact, if you can make them one or two days before you want to serve your cake, its ideal. When a cake is freshly baked, it’s very crumbly and difficult to stack. I recommend baking your cakes, wrapping them in clingfilm and popping them into the freezer, and then unwrapping and decorating the next day. It will make decorating so much easier, trust me!

Is it okay to leave the batter to sit while I bake three cakes?

6 disposable cake tins between 6 and 8 inches should fit easily into a normal sized oven with three shelves. If all of your tins can’t fit into the oven at once, there’s no harm letting half the mixture sit as long as it’s for a fairly short time (your cakes should be cooked in around 15 minutes). Cake mixture shouldn’t sit around for too long once the flour has been added, or the cake will become tough when cooked.

Does the frosting set firm?

The cream cheese frosting I recommend will set firm to the touch, although it may need some help from the fridge on a very hot day. When you’re decorating the cake, you’ll need to apply multiple layers of frosting, setting in the fridge.

I’m having problems with my cream cheese frosting, any advice?

 Cream cheese frosting can be tricky – I wrote a whole post on how to get it right here.

Could I use another type of frosting to cream cheese frosting?

Of course! It’s your Rainbow Cake. You could also use a buttercream, or perhaps a chocolate frosting. It would be really nice to try one flavoured with strawberry or cherry extract too. If you’re not too confident with baking, you could even buy a pre-made frosting. Or you could even use jam.

Lots of Rainbow Cake recipes also recommend a Swiss Meringue Frosting, which is also white and popular due to not being overly sweet. If you’d like to give it a go, try this recipe by the reliable Annie’s Eats (you’ll want to double the quantities).

Could I use less sugar in the cream cheese frosting?

Definitely! Any frosting recipe is a guide – I normally add sugar 100g at a time until I’m happy with the sweetness.

How should I decorate my Rainbow Cake?

Excellent question! The answer is – however you want! I love a smooth, plain white finish (to which you can add rainbow coloured sprinkles if you want) which doesn’t give any hint to the cake inside, so that when it’s cut, its a magical surprise! This is also the most low-maintenance method of decorating your Rainbow Cake.

It is possible to cover your cream cheese frosting in fondant if you’d prefer too.

If you’d like to experiment with your decoration, check out my Rainbow Cake board on Pinterest for more inspiration! The rainbow ruffle and rainbow fondant heart cakes are especially awesome.

Do I need to use dowels to support my cake?

My cake didn’t have any support from dowels, and it held up just fine. Cream cheese frosting is very sticky and holds the cake together well. However, when you’re building your cake, I recommend sticking it to your cakeboard/serving plate with a little cream cheese frosting ‘glue’ and building it two layers at a time, popping it into the fridge for 20 minutes each time to allow the layers to set firm before adding more.

Baking a Rainbow Cake - Frequently Asked Questions

How should I transport my Rainbow Cake?

 I transported mine in a large shopping bag (the big bag for life types from Marks and Spencer) and it did get a little knocked en route (on the BUS!). If your cake needs to be transported, I’d recommend a taller cake carrier (Lakeland and cake supplies shops do some lovely ones).

 

 Do you have any other Rainbow Cake questions? Let me know what they are in the comments and I’ll do my best to help!

x Kerry

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61 Comments

  1. Fabulous, useful advice :)

    Reply
    • Thanks!

      Reply
      • Hi Kerry, how much gel coloring did you add i each batter for the different colors (6 in total). Thks.

        Reply
        • I would say it was up to 1 tsp per colour layer but generally you need to keep going until you get the colour you want

          Reply
          • Thanks Kerry :)

  2. I used your post, along with sweetapolita and whisk kid when I made mine! – so a huge thank you! Sponge wise I just used my normal sponge base (weigh the eggs and follow from that…) & I used Tesco disposable cases (approx 8.5″) and made a 5 layer cake… the cases are great to make lots of layer cakes, I rinsed them and reused!!
    Frosting wise, I risked making Swiss meringue buttercream – and that was a big learn in itself, but great to make large covered cakes with that american look about them!
    Thanks again – great post it was!

    Reply
    • Thanks so much Holly – so glad you found it useful!

      Also I didn’t realise tesco do reuseable cases, interesting!

      Reply
  3. These are all good to know. I especially didn’t know that too much food coloring would ruin everything. Thanks for the tips Kerry :)

    Reply
  4. I live in Bangladesh and it is very tough to find gel based color only liquid based food color is available here so what will I do ?
    And another
    Question is that about the frosting can we make normal sipped cream for frosting ?
    Thank you your answer will be appreciated .

    Reply
    • Hi there – could you source it online? The recipe really wouldn’t work very well with liquid based colourings I’m afraid, though you could always try.

      What is sipped cream? You could substitute the frosting for another one of your choice definitely.

      Reply
  5. Great site… but HELP! I am trying to mix the blue layer (using Americolour Royal Blue), but it keeps turning out green (obviously blue gel and yellowy eggy sponge mix makes green!) what can I do?! The cake is for this coming weekend and the birthday boy wants different layers of blue cake!

    Reply
    • Thanks Dawn! I’ve never had that happen before – try adding more colouring? Americolor is normally pretty reliable!

      Reply
      • I have had a similar issue with sugarflair sky blue gel and buttercream (yellow in natural state like the sponge). Mine went mint green. Normally only a few small blobs are needed with gel. Approximately how much colour do you usually add to get your mix blue please?ll

        Reply
        • Hi Claire – to counteract it you could try using a paler butter like lurpack or a navy blue rather than sky blue colouring. I add it gradually, but probably add almost half a tsp! And if we were talking about a red velvet cake – gosh, its more like two full tablespoons!

          Reply
  6. Hi – do I need to grease the baking trays you bought from Wilkinson?
    Also what quantities of ingredients did you use for your icing?

    It looks so delicious, very excited about making it :)

    Reply
    • Hi Fran – the cream cheese recipe is in the post, scroll around and you’ll find it!

      Re the cases, you don’t really need to – they’ve never stuck for me, but the beauty of foil cases anyway is that you can just cut them off!

      Reply
  7. Halo there, Need advise/help

    I intend to make a 6 layer Rainbow Cake on 8ins pan. Transport the cake. Is a problem?Do u think, cake carrier (lakeland) serve Singapore?
    Btw, the Marks & Spencer…bag…u mean the their shopping bag?
    Pls help……thks

    Reply
    • Hi there- your best bet is probably a normal cake carrier – but a tall one, or else out the cake on a plate into a cardboard box and carry it yourself

      Reply
  8. Thks Ma’am
    Sorry, roughly may I know, the height of a rainbow cake?

    thks again

    Reply
    • As I mention in the post – it depends what size cake tins it’s baked in. If you bake it in 9 inch tins it will be just a slightly tall but normal cake, smaller tins and it obviously gets bigger and bigger!

      Reply
  9. Hi, can I add sponge gel to the batter? If yes, how much should I use?

    Reply
    • Hi Sharon – by sponge gel do you mean the food colouring gel? If so, add it in increments of about a quarter tsp (don’t redip the same spoon in the gel though) to the batter

      Reply
      • No is sponge gel emulsifier(to make the cake more softer texture.

        Reply
        • Hi there – I don’t use that, so I can’t advise when to add it particularly – at whatever stage you normally add it in the process is probably best

          Reply
          • Ok, never mind. Tks:)

      • No is sponge gel emulsifier for the cake texture to be more light n softer

        Reply
  10. Hi, how long will the sponges keep, before they are decorated.Thank you

    Reply
    • Hi May – they should be fine tightly wrapped in cling film for 2 days.

      Alternatively you could bake the layers, wrap them up and freeze them and defrost them when you’re ready to use them – stacking and decorating them is much easier when they’re partially frozen

      Reply
  11. Hi Kerry,

    I think my Googling has been either patchy or unsuccessful, but I thought it better to ask after all that than to continue to wade in confusion! My question is: are paste colours the same as gels? Can they all be used in the same way? I was leaning towards Wilton pastes as they were clearly labelled as being vegetarian/vegan, but my searches seemed only to bring up Wilton icing colour pastes. I googled, and couldn’t find anyone mentioning that this was what they used to colour the cake itself. The description for these pastes suggests colouring icing, mashed potato, and pastry, but not cake batter. Would this same paste be fine for cake batter? Or do they make a separate range of pastes that I’ve just missed?

    Reply
  12. Hi There,

    Beautiful Cake!!!Tried to make it. I am mixing wilton colouring in the batter and baking the cake. By the time the cake is baked it is turning out Brown and no colouring is left. But the batter i am using is very vibrant in colour. What should i do? It takes total about 30 mins to bake my cake.

    Awaiting your help.

    Thanks

    Reply
    • Thanks for your question Dishita. Are you baking each layer of the cake for 30 minutes? Since they’re so thin, they need probably ten minutes max each, so that could be the reason the cake is over-browning. I also generally swap my cakes around in the oven to a lower shelf if any of them look like they’re getting too brown.

      Reply
  13. Hi there. Isit ok to use Betty Crocker Classic gel food colouring? Thanks

    Reply
    • Hi Mani, I’ve never tried it so I can’t give advice on it I’m afraid. Do some googling maybe and see what other people have thought of it?

      Reply
  14. which cream cheese should I use for the cream cheese frosting?

    Reply
  15. Hi I’m looking at making this cake are the bakers toolkit colourings ok to use? I’m not sure if it’s gel? Thanks

    Reply
    • Hi Jo, thanks for your question :) What is the bakers toolkit? It really needs to be something that’s described as a gel or paste colour. Is it in a very small tub?

      Reply
  16. Hi Kerry
    I want to make your cake for my daughter’s birthday party which is a day after we return from holiday (seemed like a good idea at the time…!). Do the layers freeze well? I was thinking I could make the sponges, freeze them, go on holiday and then defrost and construct upon our return.
    Thanks
    Joanna

    Reply
    • Hi Joanna,

      The layers do indeed freeze well – what I would do is remove them from the cases once they’re cool, and carefully wrap in clingfilm individually (they’re crumbly when just baked). Pop into the freezer and then you can construct the layers when you get back – you don’t need the layers to be defrosted completely to do this, and it will even be a lot easier if they’re frozen! You can then pop into the fridge for the frosting to set overnight, and then just leave the cake out to come to room temperature before the party.

      Hope that helps!

      Have a lovely holiday!

      Reply
  17. Rainbow cake – Can I decorate my cake in advance (night before), where is the best place to store it?

    Thank you.

    Reply
    • Hi Shyla – in advance is always the best! I would store in the fridge to help the frosting set firm, just make sure there’s no raw onion or anything else smelly in there!

      Reply
  18. hello Kerry, i am planning to do this for my niece’s birthday as part of a stacked cake. Would it be safer doing this as the top tier or would this hold other cakes?
    thank you!

    Reply
    • Hi Ade! It depends what the other tiers are and how you’re planning to cover them. You’d probably need to cover in something like ganache and then fondant to make it hard enough to support the weight of another cake- and you may need dowels too. But I’ve never made a tiered cake I’m afraid so I can’t advise for sure. Try googling / asking on twitter?

      Reply
      • thank you – i will probably use as the top tier

        Reply
  19. Hi Kerry how i hope you can help me, i want to make this cake but i need it to be 10 inches. How do i alter the ingredients so i have enough for 10 not 6 thanks Belinda

    Reply
  20. Hi Kerry,

    Can you say why you specifically don’t recommend Dr Oetker gels? These are all I have and I don’t have time to source others brands before I need to make the cake. Just wanted to know why you don’t recommend them so I can be prepared/change my plans. Thanks in advance!

    Reply
    • Hi Sarah! I’ve seen various people, including on the comments on my rainbow cake post use them and they don’t produce vivid results.
      I’ve also used them to make other things and found the same thing, so I’d always recommend that if you’re going to the trouble of making a rainbow cake to get them. X

      Reply
      • Thank you! I’m aiming for more pastel colours than full on bright colours so hopefully the Dr Oetker gels will be okay for this cake :)

        Reply
        • Ahh in that case it could be fine! Just be sure to not let the cakes get too browned by rotating in the oven. Id love to hear/ see how it turns out!

          Reply
  21. hi..i tried this..in the case of purple colour, the edges and the base of the cake turned green.. however the inside remained a deep purple colour..please help..all then colours worked out except this one.. I would be indebted to you for your help

    Reply
    • Hi Bisma, What type of colouring did you use?

      Reply
  22. Just wanted to say a huge thanks Kerry for your post. I made this cake over the w/e for my friends baby shower and despite never having made a cake before it turned out amazing and proved to be a real hit!! Not only did it look stunning it tasted fab. Your detailed instructions gave me the confidence to just go for it! Thanks very much.

    Reply
    • Thank you Mandy – I’m so pleased it turned out really well! :-D

      Reply
  23. Hi Kerry,
    I baked this rainbow cake for my daughter’s 9th birthday and it turned out brilliantly. I added too much red to the first ‘orange’ one so ended up doing that again. I should have added yellow first and then a teeny tiny bit of red to make the orange. My daughter also wanted a pink layer so it ended up being 7 layers. Tasted as good as it looked.
    Thanks again!

    Reply
    • Wonderful to hear, thank you so much for letting me know Fiona!

      Reply
  24. Hi!just wondering have you ever tried to make a bigger rectangular cake, I was thinking of using Swiss roll tins.thinking of it for birthday cake.thanks!

    Reply
  25. I used seven minute frosting, which is made using egg whites and so a pure white colour. It turned out really well. This is the link to one that looks okay, although I used a recipe from a dairy cookbook. When the sponge is coloured, it is really nice to have a pure white frosting.

    http://www.food.com/recipe/no-cook-7-minute-frosting-107841

    Reply
  26. Hi Kerry. Im currently busy making your amazing rainbow cake. I made the cake mix exactly as your recipe but the layers did not rise much. Did I do something wrong? Your cake layers looks double the thickness of mine..
    Would love to hear from you!
    Thanks so much x

    Reply
    • Hello! What size cake tins did you use?

      It’s possible that the baking powder might have not worked, baking powder becomes inactive over time so it’s worth buying a fresh pot, especially for important cakes

      Reply
  27. Hi Kerry, thanks for the great tips. I am a bit of a newbie to baking and going to challenge myself with this one. I have a few questions:
    Can I cover this in fondant icing on top of the buttercream. Thinking of doing it quite plain for the surprise when it’s cut :)
    Can I bake the cakes on Saturday and refrigerate until Sunday to be built for serving on Monday?
    When colouring the cakes, will the cakes come out exactly the same shade as the batter?
    Thanks :)

    Reply
    • Hello! Thanks for visiting my blog!

      Fondant will be absolutely fine, I’d roll quite thin and put on top of a thin layer of buttercream, but it’s quite a sturdy cake so it should hold it up no problem.

      Timing wise, that sounds perfect. The cakes will be nice and firm and you can use sunday to build and cover the layers in buttercream and then allow to set before covering with fondant.

      The cakes are just as bright, so your batter needs to be extremely bright, don’t be shy of adding lots of gel colouring until it’s virtually neon! When cooking them, rotate the pans and don’t let any get brown – have them on the middle shelf of the oven. Good luck!

      Reply

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