Unpleasant smell

My cider took almost 10 days to quit bubbling out of the air lock. I gave it another day, then pulled the air lock and used a sterilized siphon to get a sample for the gravity, which came out to .996 1/2. (Used EC-1118 yeast) After tasting the sample, it wasn't bad. Very dry and little alcohol taste, but after swallowing, you could feel the warmth in your mouth and throat. A little Stevia added and it was quite pleasant.

I put the air lock back on, and it started bubbling again for @ an hour.. assuming the yeast eating up the oxygen that got in during the sampling? That evening, I put the cider out in the garage to cold crash it since it stays in the low 40's out there right now. After 3 days, I went out last night to transfer it to a secondary. The air lock liquid was level, indicating no pressures had built up, but when I removed the lid to siphon, it now has a DEFINITE sulphur/yeast/sour smell, and the taste was not pleasant at all. Did something go bad? Did I leave it on the yeast too long? Is it something you think will age out, or do you think the batch got infected somehow? I always try to be extremely sanitary, but how can this cider go from pleasant, to awful in 3 days?

This is pretty normal, do a search on 'rhino farts' for a million threads on the subject, it's the result of yeast stress, in this case probably caused by the rapid drop in temperature and the lack of yeast nutrients left in the juice at this point. Since the batch it done, consider racking today, it may remove the smell.

I did rack it to the secondary last night. I'll leave it out in the cold for a while more before bottling.

Never heard of rhino farts before.. but will check into it. Thanks. I just didn't want to make a big batch of apple vinegar.

After reading up a bit, I don't see any obvious reasons people get the rhino farts. Seems someone does the exact same method as someone else, and one gets it, the other doesn't. I guess between the bit of oxygen getting introduced, as well as the cold temps, I put a damper on the happy little yeast orgy in there, and it responded by showing me it's displeasure...

I'll leave it in the secondary and take a whiff out of the air lock once a week. I see that you don't want to bottle it with that sulphur smell going on.

Either way, I guess it's all good. Worst case scenario.. I've got 5+ gallons of coffee pot lime remover. lol.

Rhino farts are different from acetobacter, which is what makes cider into vinegar. But over time the smell, which is hydrogen sulfide (H2S) will bind into more complex and difficult to remove molecules. I wouldn't consider it a major or urgent problem, and giving it a couple weeks rest is probably the best bet at the moment, but other solutions include degassing by gently stirring or racking, adding sulfites, adjusting the temperature, and stirring with a copper rod (which binds the H2S into a blue/black precipitate which then falls to the bottom of the fermenter or stick to the rod.

A copper rod? Ugh... I keep envisioning taking a nice cold sip of cider.. and having it taste like I just sucked on a penny. lol.

Yeah, there's a reason I put it last in line. More of a worst case scenario solution when nothing else works.