Buttercream is a mixture of butter and sugar that is used for spreading or decoration. Swiss buttercream is made by warming eggs and Italian buttercream is made by cooking sugar. Adding flavourings such as vanilla or fruit makes this mixture versatile. If you want to add colour, use shortening instead of butter. Butter makes the mixture yellow, which means that it is difficult to get certain colours such as blue or pink.
Adding butter to a Swiss buttercream mixture that is to hot makes it looks soupy and lumpy. The mixture needs to be chilled and then whipped again.
Chill the mixture by placing the bowl into a larger bowl filled with cold water. Add some ice cubes to the water to make it chill faster.
Beat the mixture thoroughly using a standing mixer or handmixer is fine. Use medium setting and continue to mix until smooth.
Don't throw away Italian buttercream with lumps. They recommend applying heat to make the mixture come together. Chill the mixture and whip it again.
A mixture can look curdled before you have added all the butter. Continue whipping and after the beating, the mixture will look smooth. Usually it takes a couple of minutes, but it may take up to 10 minutes.
Adding flavours to a buttercream can make it lumpy. Lighter flavours such as vanilla and lemon juice can be added during the whipping. However with heavy flavours such as chocolate, the fruit should be added after the whipping.