Ok so I don't know what the crap happened today. It was an unusually warm day (in the 80s) and we didn't have the air on. I was making IMBC for an order, I have made this frosting sooo many times and had some fails but never FOUR TIMES. I couldn't get the past the stage of pouring the sugar into the egg whites. It seemed like the egg whites were too hot and deflating the meringue. I tried chilling my bowl and egg whites and it didn't help! I wonder if it's because it was a hot day and I was using egg whites from a carton instead of cracking them into the bowl? I have used those egg whites before though and not had an issue. Can anyone advise me? I ended up being really unhappy with the runny icing I had today :( Luckily it was just for my friend's mom but I have an order for the weekend that needs this icing so I need to make it tomorrow to be sure it's ready in time! Yikes. I hope I can do it tomorrow :/
I've never used whites from the carton, but many others have said they don't whip up the same. Did you use cracked egg whites in any of your attempts?
I usually make mine ahead of time so mine is ALWAYS runny. LOL! I often don't get the egg whites up to peaks and I never wait for it to cool down before adding butter, so I always end up with sweet buttercream soup. I prefer this, because when you put it in the fridge overnight, it stays soft instead of turning into a rock. So when I whip it up to use, I don't have to melt it first! And then once it reaches a certain temperature it starts whipping like magic. No problems.
As long as everything is scaled correctly (and there's no sugar crystals during boiling), then it's just a matter of heating it up if it's lumpy/solid, or chilling it if it's soup.
The carton egg whites have to be shaken really well... I've only had an issue with them once, and I think it was because they'd been in my freezer for several months. If you originally had a meringue, I don't think your hot sugar would have destroyed it...
AI use the cartons as well but I add cream of tartar after everything is mixed up, it'll fluff up nice even in high humidity! Good luck!