Buttercream and frosting are both made with powdered (icing) sugar, fat, flavour and milk or water. What makes the difference is the type of fat use in both.
Frosting doesn’t contain butter. That’s the big difference between buttercream and frosting . Frosting is usually made with shortening (Trex, Flora White & Cookeen) or cream cheese. That’s why frosting is a good option if you want a bright white cake than buttercream which often has a yellowish tint.
However, shortening-based frostings can have a slight chemical taste. This is because unlike butter, shortening has no flavour, making it easier to taste any artificial flavourings from food colourings or other additives. Best to use the highest quality extracts, essences or vanilla bean pastes when making frosting.
Vegetable shortening is a white, solid fat made from vegetable oils. In the UK it is sold under the brand names Trex, Flora White or Cookeen.
This is a butter-based (Unsalted butter) frosting. The butter gives the icing a richer and creamier taste. For silky smooth buttercream, make sure the butter is at room temperature. Chilled butter can be harder to work with or cream.