Refrigerate until serving, but best served within a few hours.
Remarks
This is a simple mousse, just a mixture of meringue and stewed rhubarb. It is quite fragile, so does not keep and should be eaten the day it is made. If not, it will deflate or compact at the very least.
If you are in a hurry and don't have time to make Italian meringue, French-style meringue will also work.