I made a huge batch of Swiss Meringue Buttercream last night and it was PERFECTION! Put it in the fridge last night and then pulled it out about an hour or two ago. Started to re-whip it and it is just a curdled mess. . .put it back in the fridge for about 15 minutes and pulled it out again and noticed a very liquid substance on the top (melted butter maybe??). . .whipping it and it is not coming together. . .what happened????? Should I put it in the fridge longer than 15 minutes and try again?

I mean this stuff was perfect last night, I am SOOO upset. I need to start this wedding cake and really don't want to make another batch of icing.

I'm no expert on SMBC since I have only started using it myself but I believe that it should reach room temperature before you start rewhipping it. It might have been too cold. Hopefully someone more experienced can advise you on how to save that batch. Good luck.

Ok I found this on Sweetapolita on the subject. Hope it helps.The great thing about SMB is that it can be made in big batches and frozen, or refrigerated for up to a week. The only thing is you need to take a moment to reconstitute it back to its glorious satiny texture when youre ready to use it. If its frozen or refrigerated, you need to thaw it at room temperature; this can take overnight if its frozen, and several hours if its refrigerated. There are a few ways you can revive it, but I do 1 of 2 things: 1. I take the thawed (but sometimes still cool) SMB in a microwavable container, and I warm it up for about 10 seconds, then remove container from microwave and stir it aggressively with a rubber spatula in kind of a back and forth motion, repeatedly until its smooth. If I think I need to warm it up a bit more, I microwave again but am careful not to melt it. I mix it really well with the spatula, to remove the air bubbles. 2. I take about 1/3 of the SMB I thawed and I warm it up by the above method, and put the remaining 2/3 in the electric mixer bowl. I add the 1/3 warmed SMB to the 2/3 cool SMB and mix on medium or medium-high speed with the paddle attachment (flat beater) until smooth and satiny.

I have had this happen, too -I got so frusterated I walked out of the kitchen while it was still whipping - about 15 min I came back, and it was all better!
It takes a long time to be whipped back to perfection - now I know that and you just have to get through that nasty curddled phase.

It's like putting a stick of butter in the fridge, to explain it as simply as possible. If yuo want to be able to spread the butter, you have to wait for it to come to room temp. That's all!

so don't put it back in the fridge- use the whip attachment and let it whip for awhile----do something else while you wait!

It's totally fine! Let it come to room temperature. (I rush this a bit by putting it in the oven with the light on. DO NOT turn the oven on.) Then put it back in the mixer with the paddle attachment and let it go til it comes back together. The liquid will mix back in just like it was last night.

For future reference, you CAN leave it out of the fridge overnight.

I have been using the same butter brand for years and never had any problem. But recently I changed suppliers and I started having that exact same problem, this happened too with my chocolate ganache.
Some butters contain more water than others, try to go for another butter and I´m pretty sure you won´t have this problem again.

Fridging and then mixing was your problem as the PPs stated. It's an emulsion, and you just broke it. It will come back together (let it warm to RT naturally or melt 1/3 of it and mix it back in or mix it with a torch of the side of the bowl) but it will likely not come back to it's full volume and it will be heavier.

Another tip for bringing back cold SMBC if you are using a stand mixer; is to take a dish towel and get it wet with as hot water as you can stand and then wrap it around your stainless steel bowl as you whip it. It will gradually warm up enough to go back to smooth.