The first post I made about foam* was supposed to include some of these photographs. Instead, I kept it about soap foam.
This time, the foam has to do with the protein content of the photo subjects (Links about food foams: 1, 2, 3)
This foam formed on top of boiling beans (hence the dark bits)
You guessed: beaten egg whites
Coffee in hot water
This foam formed during the first days of beetroot fermentation
I took the photos with my Redmi Note 8 and edited them with Snapseed.