. The primary ferment of which the images are of i threw away yesterday because i thought that scum for surely meant it was ruined and i was told plastic is porous and could hold contaminants and the primary fermenter i used for that batch i bought used and it was kinda rough looking. But the other batch of apple rubarb i made in a brand new 32 L container is still getting that scum just not as aggressive. When i stir the apples and rubarb there has been less film forming on top it still smells alright. I have two primaries with only apples and there is no scum on those just the two with apples and rubarb got it. I washed the rubarb really well and cut off the ends.