Hi

Apparently, meringue frostings (where you add hot sugar syrup to egg whites) are only ok at room temperature for 1-2 hours.  The same is true for cream cheese frostings.  Is it because these frostings are unsafe to eat after 1-2 hours or because it affects their flavor/texture? I find this confusing because mousseline buttercream is fine at room temperature for 1-2 days and that’s just meringue with butter added to it! Can anyone clarify, please?

By meringue frosting, do you mean Rose’s Light Italian Meringue recipe? 

In general, I think it’s probably a good idea to keep dairy (like cream cheese) and eggs in the refrigerator until a few hours before serving. 

That said, I’m wondering if the main problem with leaving meringue out is that it will continue to attract moisture from the air.  The other issue may be sugar content.  A high saturation of sugar creates a hostile environment for microbes, for example, the Royal Icing recipe will keep at room temp for three days.  The Light Italian Meringue has the minimum amount of sugar that will still stabilize the foam and so may be less hostile to bacterial growth. 

Mousseline has all that butter, which works to moisture-proof the meringue. 

As for cream cheese frostings, Rose’s white chocolate cream cheese frosting is good for 1 day at room temp.  If you are looking at a recipe that doesn’t contain white chocolate and lemon juice, then it may have different keeping qualities.

Thanks Julie, for all the information.  Yes, I am talking about Rose’s Light Italian Meringue recipe.  I didn’t know all these things about meringues and I will keep these things in mind.  Is Royal Icing safe?.........I never make it as it uses raw egg whites and I am afraid of salmonella.

I noticed that Rose’s white chocolate ganache is also ok for 1 day at room temperature and she says it is because of the white chocolate which stabilizes the cream.  I am wondering if just the white chocolate will be enough to stabilize the cream cheese as I dont like lemon juice in my cream cheese frosting. I have been flipping through my cookbooks for a few days, and noticed that Alisa Huntsman (a pastry chef who graduated from the Culinary Institute of America) has a white choc-cream cheese frosting in her book which has no lemon juice in it.  Yet, she claims that once the cake is covered with the frosting and then the fondant, it will be fine at room temperature for 2 days! So, I guess as long as you stabilize the cream cheese with white chocolate, you can keep it at room temperature for at least a day.