Every once in a while, the confectioner sugar will clump up hard. I really have the same routine every time making it, but can't figure out why it does this. Has anyone else encountered this and figured out why? MY thoughts are maybe the butter is chilled a little and causing it to freeze up, but the butter is never that hard when I put it in the mixer. I do always beat the butter really well. Sometimes I do use my whisk instead the the beater attachment(it was with the whisk this time I know it happened). I add my sugar slowly, but don't ever sift it.. I did feel it and there seemed to be no lumps in it to start with. I have also had many different brands of conf. sugar and have had it happen with a couple of different brands that I remember. HELP!

When I make buttercream I always sift it. Even if it feels very loose. Youd be surprised how many small clumps can be found Try sifting it next time and see if it still happens.

Try running your buttercream through a food processor after mixing it with a paddle. That should eliminate any remaining lumps.
- Kristen

I was taught that if the powdered sugar package was brand new and unopened I didn't need to sift it. But if I am going to use an opened package, then I needed to sift it, which I do. Moisture can get in to the package and give the sugar lumps.

All b'cream recipes should be mixed at low speed for at least 10 minutes...even more will make it smoother.
Are you sifting your sugar? It does help to have to butter at room temp but it's not totally necessary.
Don't rely on a new pkg of sugar not neding sifting! There are many factors that can effect it.
Once when teaching a lady was having trouble w/her tip pluggin up all the time.....repeated clearing it still plugged. Finally found a 1" piece of plastic bag - and then others mentioned they too were having trouble....so that run of bagging sugar had lots of bits of plastic through it! You never know what might happen