Alright! We need someone to test this! Who will volunteer to get a stick of unsalted butter and leave it out for months? 
You must provide pictures!
Hey everybody, if you’d like to view an ancient USNET story from 2006, you can see many of the topics in this current thread in that one. Click it here for the Google Groups archive.
It was the shouty bit that I was saying was not supported by dictionaries. 
You know: “RANCID != ROTTEN”
Wrong!
It typically does mean rotten.
‘Rancidification’ is listed in the OED as a ‘Manuf. Technol.’ word.
Rancid is the everyday word that has a much less specialised meaning. ‘Rancid’ is at least 200 years older the ‘rancidification’
Absolute nonsense.
“RANCID != ROTTEN” clearly contradicts the normal definition of ‘rancid’.
That rather prompts the question: “Why died and made you God?”
Why do you think that you have some authority to dictate that people should not use a word that has existed for nearly 400 years with its normal meaning just because there is a more specialised word that you prefer?
That strikes me as an unbelievably arrogant attitude. You may not have intended that but your continued insistence that everyone use a word in the way you want it used certainly gives that impression.
I usually try to stay out of “word usage” fights but I can’t help but point out that it looks like the OP’s question has been answered in that there were explanations provided as to why butter doesn’t “go bad” in the way that many foods do.
So to quote my dear old Uncle Floyd - “Ya know, is the fact that they are actually bison any more important than the fact that just about everybody calls them buffalo?”
I suggest you go back and re-read my OP. There I attempted to ask a question about why fats do not grow mold. After seeing the responses, I saw that some people may not be interpreting my question in the way it was intended, that just because fats become smelly etc, does not mean they are rotting – ie infected with bacteria. In fact in my OP I wrote:
Where I thought it was obvious by implication that the definition of rancid that I was using was the scientific one: that rancid == chemical change => rancid != moldy => rancid != rotten. But since it seemed some responses seemed to be conflating bacterial infection with the chemical process by which fats become bitter, nasty smelling (ie ‘rancid’), I thought I would clarify by writing in my next post:
Now you may be correct that this is an oversimplification, but your response completely missed the point, which was (executed clumsily I will admit) to let people know that in my question I was assuming the narrower, more technical definition of ‘rancid’: of a chemical decomposition, as opposed to bacterial. I wanted to know when fat becomes moldy, not when it becomes ‘rancid’ or oxidized, as is typically referred to when the oil in your kitchen or anything oily and non-moldy in your kitchen goes ‘bad’ it is almost always due to oxidation, and called ‘rancid’. This is very common usage, and is amply documented in wikipedia (i gave links earlier), brittanica, etc, if you would care to read the articles, as well as most dictionaries I have consulted (although I admit a few make no mention of oils, but I find this in stark contrast to other dictionaries which make the connection very clear. i have no access to the oed). It is certainly a commonly understood definition in my neck of the woods and social circles. If someone smelled a bottle of oil and said “ugghh, this oil is moldy!” I would correct them: the word you are looking for is ‘rancid’. It is in that spirit that I say “RANCID != ROTTEN”. Is this really an “unbelievably arrogant attitude”?
I know, we are like little children (or maybe we are little children), it’s pretty embarrassing, but we ain’t harmin’ no-body. Yet. 
And yes I think I’ve got my answer to this question. Thank you all!
I would volunteer, but I’ve done my bit for science. A friend and I once discovered a potato slowly decomposing in a desk at school, and decided not to interfere. This is how I can tell you with authority that a perm smells like a rotten potato.
Rendered or “clarified” butter, which has had the milk solids and water removed, has a much longer shelf life than butter. It’s quite fine at room temperature for extended periods, much like rendered lard.
I think the problem was that when I read your ‘clarification’ I didn’t look back to the top of the thread and didn’t realise you were the OP. Thus I thought you were just nit-picking. By the time I realised you were the OP we had already begun discussing the ‘rancid’ issue.
And I do like a good arg^h^h^hdiscussion.
There’s a stick of non-salted butter in my cupboard that has been there, opened, for, I think, two months (and there have been hot days, part of it melted). It doesn’t smell bad and just looks more yellowish and more jellyish. I’m not going to eat it, but it looks like it might possibly be edible.
Is that you, Grandma?