I read somewhere that sugar "preserves" a buttercream frosting i.e., the cake can be left "out" and not refrigerated. True? Thanks for your help. Cassie
I have heard it before as well - I have to email my Food Safety teach a few questions - that is one of them. How long can I leave out a cake that has been frosted and "fondanted". I will let you know when I hear back from her.
I read somewhere that sugar "preserves" a buttercream frosting i.e., the cake can be left "out" and not refrigerated. True? Thanks for your help. Cassie
If you're referring to the tiny amounts of milk or cream used in American b/c recipes, you're correct.
I have provided information that sugar is hygroscopic (or moisture absorbing) so it can be used to alter the "water activity" in American b/c made with cream cheese:
http://cakecentral.com/cake-decorating-ftopict-582086-.html
Not being a food scientist, I wouldn't attempt to "doctor" a perishable cake frosting or filling recipe with sugar to make it shelf stable.
For example, adding a little extra powdered sugar to a basic whipped cream frosting IS NOT going to make it shelf stable.
Speaking in generalities, is probably not a good idea when it involves food safety issues. For example, the stable cream cheese frosting recipe I posted may be vastly different from yours; so the results of not refrigerating yours could be disastrous.
If you have questions about a specific recipe, please post it, and I'm sure you'll get responses. 
Edited to fix broken link.
I read somewhere that sugar "preserves" a buttercream frosting i.e., the cake can be left "out" and not refrigerated. True? Thanks for your help. Cassie
Love the quick responses. I'm using a buttercream recipe, a combination of shortening and butter, I found the recipe "Crusting Buttercream Icing (Viva Method) on this site. The only change I've made to it is to add milk (at most 1/3rd cup) rather than water. I'm not using cream cheese, or whipping cream. It sounds as though you agree that it is safe to leave out for a couple of days?? Once more, thank you for your help.
Your recipe should be fine.
However, using milk or another liquid with fat can affect the crusting (the more fat, the less crusting).
HTH
Help? It's more than I asked. Now I know that I can have the cake on the counter for a day and feel secure about it, AND that I should use water instead of milk for a better crusting effect. Thank you so much, Jan, there is something to learn everyday and this is the site from which to learn. Cassie
Thank you for pointing me in a useful direction i.e., searching for refrigeration... I used to read info on 911, but gave it up when the cost was instituted. I feel more comfortable going ahead with my baking now. Cassie
No problem! I would love to know if you find some more concrete info on this topic. I am so sad I can't look at the info on 911 anymore. I wish I would have copied those posts when I had the chance! -Anne
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