I have some 05 yeast that’s been sitting in a carboy for about two weeks in my basement. Think it would still be okay to pitch the yeast cake onto a new batch or should I toss it?
Covered with beer the yeast will still be good. I’m not a proponent of pitching on to an entire yeast cake. I will take part of the yeast make a 500 or 1000 milliliter vitality starter on brew day. Size of the vitality starter is dependent on the OG of planned beer. About 1.060 and up a 1000 ml vitality starter. How much of the yeast to use depends upon how much non yeast material is visible.
I like to use the yeast or pitch on it immediately after racking the beer off. But as @flars said, if it has been covered with beer, it should be OK.
I have pitched right on yeast cakes and had explosive fermentation but usually save some in a mason jar.
Yep, I would use it. Of course, I’m also kind of a sucky brewer, so… 
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I wouldn’t use it, and I engage in high risk brewing activities pretty regularly. The problem is that when you transferred beer out of the carboy, you pulled in whatever air was in the room in which you racked it. Air is full of mold spores, acetobacter, and all kinds of other things that love beer and oxygen together. If you purged with CO2 it would probably be ok, but the funk has had a couple weeks to grow in there, and the oxygen is all it needs to get going. Then you add your fresh wort, and there’s no guarantee that you don’t have a viable population of some other microbe. Plus a fresh pack of 05 is like 5 bucks. Practice safe brewing in this case, and don’t risk an infection!
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It may be alright but I wouldn’t pitch to it. I prefer to pour the cake into measured jars so I know how much I’m pitching. Sitting around in the basement for a few days? I don’t know like PC said yeast is cheap
After I ferment, if I want to reuse yeast at a later date, I will transfer to a container that I can seal/cover and store in the fridge with at least a 1" beer cap on it. I have no confidence using yeast sitting in a carboy/fermenter in the basement for a couple of weeks… Sneezles61
