Originally Posted by AnitaK
If you have butter and/or milk - you must refrigerate in your buttercream. I sure wouldn't drink milk that had been sitting at room temp for weeks and I wouldn't eat icing with milk or butter for that long at room temperature.
You're not comparing apples to apples....
Liquid milk is very perishable. However, packaged powdered milk is shelf stable for quite some time. What's the difference in the two products that accounts for the disparity in shelf life. Answer: water content and water activity.
(For info on how to control water activity see below.)
Originally Posted by Cakepro
Ummm, okay. If you choose to believe that you must refrigerate, that's fine. I will rely on the science
behind the knowledge that it is perfectly safe for a standard American buttercream made with butter and a few tablespoons of milk to be left at room temp for a couple of weeks.
Here's the science.
Water activity & microbial growth:
(Prolonging Bakery Product Life.)
WJ Scott in 1953 first established that it was water activity, not water content that correlated with bacterial growth:
Formulating for increased shelf life:
(Decreasing water activity results in hostile environment for bacteria.)
Shelf stable cream cheese icing: