I have a Swiss meringue buttercream recipe that has a water activity of 0.863. I’m trying to reduce the water activity to 0.85 or lower using a humectant so I can keep the frosting at room temperature. Internet research led me to want to use vegetable glycerin, so as not to affect the taste and texture of the frosting. However, I have no idea how much glycerin to use to accomplish this, and would like a better idea before I spend the money to lab test it. Recipe is below. If someone could help me, that would be amazing. Thank you!
160g pasteurized liquid egg whites
4 sticks (453g) unsalted butter
300g cane sugar
2 tsp vanilla extract
pinch of salt
The egg mixture is cooked to 160 degrees before adding butter.
As a humectant, I belief that glycerin may help you to lower the water activity of your product. But functionality is influenced by many factors including the composition of your recipe and the preparation method. So, here is my suggestion, since you are experimenting, why not vary the level of glycerin added so as to better identify the best level for your specific recipe You could start with a small amount and adjust as needed to achieve the desired water activity level.