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I'm currently brewing a 3kg ESB Czech Pilsner pack. The pack has all fermentables including hops - i made it up to around 22L. There is this weird green foam that covers the surface relatively evenly. Am i right to say that this green layer is a combination of both hops and the lager yeast? Is this because the hops float and the lager yeast is top fermenting? The fermenter is bubbling away nicely and the gas has a slight sweet aroma to it.
Lager yeasts are bottom fermenting. So its not the yeast but as the others have said hops and krausen. A healthy foam on top indicates fermentation is nicely kicking on.