Can anyone tell me if this is harmful, or what I need to do? It’s about four gallons of apple must that sat for one day before I added 1/4 tsp potassium metabisulfite yesterday morning. Should I pitch my yeast into it and see what happens? I have not seen this white mold-looking growth in any I have made before. Hate to think I will have to pour it down the drain. 
Thanks!
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Filter off the top and bring it to a boil for several minutes. Let cool to yeast temp then ferment away. You can separate it by freezing the top 1/16 inch and lifting it off.
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You got flower. No good news. It consumes alcohol in the must. Skipping it out as much as you can
Yeah, depending what it is, it is probably only on the surface because that is where it is exposed to air. If it actually is mold, I’d be wary of drinking because of the potential of being contaminated with mycotoxins. I’d try to skim it off the top with a paper towel ASAP or rack it to a different vessel from the bottom. Hopefully your sulfites will have kept it from spreading and you can get it fermenting under airlock soon.
Just curious, what is the PH of your must? I think when it is a high PH it is more prone to bacterial infection and may also require relatively larger dose of sulfites than low PH. I added acid blend to a pressing of dessert apples about a month ago because PH seemed to be in the 4 range and I was paranoid, haha.
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PH was about 3.8, so I added about 31 grams of malic acid (4 gallons in bucket) which brought it down to 3.6 PH.
I had read it might not be a mold, but instead yeast “islands,” and so stirred in the iwhite growth along with the malic acid, and then pitched the yeast, sealed the lid and put on the airlock. I figured I’d look at it again tomorrow and see what it’s doing. Live and learn, I guess.
That was my first thought (yeast islands) How did it turn out?
Turned out to not be a problem at all. It’s been in the carboy for secondary maturation about a month and it looks fine. Thanks for asking!
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