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I made about 23 L of cider last week. I tastes great, and no issues in the bottle. However, I had about 1L left over in the carboy, and I was going to add more juice to it to make another batch. When I went back to the carboy (which was sealed with a water lock this whole time), there was a weird white film on top. It looked almost like cream that spread out from the middle of the carboy. Any idea what type of contamination, if any, this is?

Ahhh, the throw it out kind!!

Haha, well I tried a taste, and it tasted fine, but there was definitely something growing on the surface.

Doesn't sound good.

Yeah I don't think I would mess with that. Pour it out