Out of 5 small batches of cider, this is the only one that looks funny. Juice was unpasteurized and treated with potassium metabisulphite per Andrew Lea's book dosing.
Smells ok and MAYBE a slight tinge of tartness. Have not tasted it. The pic shows a thin slightly opaque white layer with little bubbles that ALMOST look like there is a slight line or ridge connecting them.