Hi!
I need some help refining my crumbcoat-to-fondant process. I achieved my cleanest crumbcoat ever last night only to find the most hideous bubbles, a.k.a blowouts, under my ganache. See pics below before (last pic) and after blowout, I was too freaked out to take a picture of the HUGE bubbles.

I'm in the process of switching to ganache under fondant so this is a practice cake.

Apart from keeping the room temperature even lower next time as I allow the ganache to set (overnight), what else do I need to do to have a bubble-free experience.

Here's what I did, please tell me where I went wrong and a suggestion to fix it. Thanks!

1. Torted and filled coldish (not super cold but wasn't room temp either) cake with SMBC.
2. Covered with plastic wrap, placed weight on top (for about 30-40 mins) and then refrigerated overnight (weight stayed on top all night).
3. Next day, pulled from fridge, and about 20 mins later covered with ganache. Figured the SMBC wouldn't mix with the ganache if it's still cold during the crumbcoat. The ganaching process involved some back and forth (average 10 mins each) in the fridge to get sharp edges.
4. Left ganached cake at room temp overnight.
5. Blowout in the morning

I live in TX where it gets so hot, even with the AC on, some days it's a challenge to keep the house especially the kitchen at 78F or less hence my reason for working with a cold cake when using SMBC. But cold cake is my problem. I'm thinking of eliminating step 2 and going straight to ganache might help but won't the SMBC get all up in the ganache? I'm trying to avoid a ganache dam if I can help it.


pics:

U have nice edges
Al wondering why aold u have that . I alwyas use ganache to cover the cake with high heat and humidity in middle east with no problem but i use ganache as filling also

I think u better use dam around smbc filling . So it prevents it from bulging out

I hope I could help

Thank you wafawafa. Yes I've decided the dam is my best bet. I found a couple of threads on blowouts and read up on them. Other tips I found:
1) poke a hole down the top-center of the cake after it's iced
2) break the icing-board seal at the bottom of the cake after it's iced using a knife or spatula
3) Leave one or 2 thin straws on the sides of the cake where I plan to put decorations.

I'm cutting out overnight refrigeration and will only do the short bursts needed to firm up the ganache during crumbcoating.

Hopefully, this should help prevent the problem. Ugh, I hate those things!

I only use SMBC as a filling and only use ganache externally and have never had this problem. I also don't need to let my cakes settle with anything on top of them. There are several reasons you could be having issues, but here is what I think it could be (apologies if you know all this already):

Ratio of white chocolate to cream - Has to be 3 to 1 chocolate to cream, not all chocolate or cream is created equal, I have one white chocolate that is TERRIBLE for using in ganache and one that is tremendous. The higher the cocoa content the better. Also, make sure to use a cream with 36% fat content, if it's too high a fat content the ganache will be too soft.

SMBC Air bubbles - a lot of people like to beat their SMBC at high speed, which is a big mistake - this incorporates air into your SMBC and this could be causing blow outs, where there are air pockets. I beat my egg whites and sugar mixture on high to get to stiff peaks, then reduce the stand mixer to the lowest speed until the mixture is cool, then switch to my paddle attachment and on the VERY LOWEST setting, add the butter and let it mix very very slowly until ready - you will have ZERO air bubbles in your SMBC and it will glide on like a dream.

Ganache Thickness - I have had to cut my own acrylic cake board for the base of each tier as the cake boards in the UK are too small, they are not exact sizes, so I now have cake boards that allow for a quarter inch of ganache round the sides of the cake. If your ganache is too thin, then it defeats the purpose of using it, a thicker coating will give you extra support.

Anyway, I have never had a blow out or air pocket in my ganache and I don't use a damn of ganache around the edge of my cakes - it's SMBC right to the very edge of the cake and then a crumb coat of SMBC on the outside, then a quarter inch layer of ganache outside that.

Anyway, hopefully that has helped somewhat.

Thank you nanefy for such a detailed response. I printed it out and will be going over it again for my next cake. I used Callebaut's 28% white chocolate callets. 3:1 but it was still temperamental. At first it wouldn't thicken up, put it in the fridge for about 15 minutes and it became as hard as a rock even when I brought it close to room temp so I had to nuke it in the microwave (that did something weird to the taste, can't really describe it). On my cake at room temp though, it became soft enough to allow the bubble push it out. I'm not too crazy about it after this happened and would be trying other brands. I've heard good things about Guittard and Ghirardelli.


Thank you for the tips!

Yup there is your culprit - I use Belcolade chocolate for my white chocolate ganache, but I have twice used Callebaut white chocolate and it is DREADFUL! Ditch using callebaut for white chocolate (the dark choc is brilliant) and see if you can get a hold of Belcolade, it's a million times better. I only use my callebaut for adding to buttercream now as it's useless for ganache - it has a lower fat content than belcolade.

Both times with the callebaut, it's been soft at room temp and the second time I used 3.5 times chocolate to cream - just as a note, always make sure you are using weights for your cream to chocolate ratio and not volume i.e. 200g of cream to 600g of white choc (you probably know that already though).

Nanefy thanks again. I'm so glad I only bought one bag. I guess now I have lots of chocolate for BC and Mudcakes.