What’s the minimum sugar to egg white ratio in Swiss buttercream?

Question

A Swiss meringue buttercream is a buttercream based on a sugar and egg white mix that is first heated and then whipped. The average recipes I could find use roughly one part egg white to two parts of sugar¹, some a bit more, some less².

I would like to reduce the sugar, but of course the sugar is not used just as sweetener, but is critical for the stability and texture of the meringue. So:

What’s the minimum amount of sugar or lowest sugar-to-egg ratio needed for a Swiss meringue buttercream?

Two side notes:

• As egg sizes definitions differ and we’re talking ratios, please either use weight or state the egg size and the locale in your answer.
• This question is not about the butter to meringue ratio. I realize that the amount of butter will influence the stability of the buttercream.

Answer 1

Sugar is used to dissolve the egg whites and the protein film on the surface of the air bubbles (source).

Looking at meringue ratio recommendations, here is what I found.

By varying the amount of sugar in the final mix, you control how hard or soft the final meringue will be. As a general rule, add a total of 1/4 cup of granulated or superfine sugar for each egg white. Do not make meringues that have less than 2 tablespoons of sugar per egg white. If you use any less, the foam will not set and the meringue will shrink.