Major overheating and not sure why

[Feelin' Soapy]

I made a 60 oz batch yesterday in a slab mold that is a silicone liner in a wood box. Used my standard recipe (lard, OO, CO, avocado, castor), no milks or other additives except sodium lactate and clay for anchoring the previously well behaved FO. Placed the wood top over it and patiently waited until the next day. Opened it to discover it overheated and cracked like crazy! Some areas of the bottom edge were a bit hard and crumbly and some of the NS Ruby Red swirls were soft. I usually use a 10" loaf mold in an insulated box and have never had an overheating problem before. Do you think this was a result of the batch being larger than my usual? Should I put slabs in the frig instead of gelling? I'm ready to give up on the slab and stick to my trusty loaf molds :-(

 

[lenarenee]

Well there's a few things; maybe the fragrance was reformulated is no longer well behaved. Maybe your water content is a little high? And perhaps just forgoing the wood lid would be enough to prevent cracking.
I don't know if the slab mold is THE issue. Yes, the mass is more, but the surface area (and potential for cooling) is larger.
Some people use a fan to help dissipate the heat. I'm leery of putting it in the fridge because should it volcano....you'll have a soapy fridge!

 

[Feelin' Soapy]

Well there's a few things; maybe the fragrance was reformulated is no longer well behaved. Maybe your water content is a little high? And perhaps just forgoing the wood lid would be enough to prevent cracking.
I don't know if the slab mold is THE issue. Yes, the mass is more, but the surface area (and potential for cooling) is larger.
Some people use a fan to help dissipate the heat. I'm leery of putting it in the fridge because should it volcano....you'll have a soapy fridge!

Thanks for your ideas. My lye concentration was my usual 35% and the FOs were from bottles I'd used before with no problem, so I don't think that was it.
Maybe I can try covering it with just plastic wrap next time? And yes, a volcano in the frig would be disastrous!!!

 

[Marsi]

I agreed - the lid on top is obviously holding too much heat in.

I would put the slab on a cake rack, and insulate it with a clear cover (your idea of a plastic wrap would work) and a towel
A hand over the middle of the slab should give you an idea whether it is getting too hot, and the clear cover means you can peek under the towel if you have to, without losing too much heat.

(Or you could try the lid again, but leave it slightly open to let some heat out, and have the slab on a cooling rack)

It sounds like you will need to fine-tune how much heat you trap for your slab - it might not be too much of a change to tame the volcano (fingers crossed!)

 

[Feelin' Soapy]

@Marsi Those are some good ideas for keeping the heat in check. And I especially like the idea of being able to peek at the soap. I'll never lose that urge to peek and see how my soaps are doing