When I make apple juice, what's in the foam on top? I juiced my peeled apple seconds. What makes the foam on top? It seems to have good flavor, but this juice is going into the fermenter for apple cider when I collect enough (freezing until then) so I'm wondering how much sugar is in the foam.
The foam is probably made up of various proteins and carbohydrates.   If you have a refractometer, you can collect some of the foam and let the bubbles fall down, and then put it on the measuring window of the refractometer, just like you would use it for the must for a wine or wort for a beer.