I recently learned that peanut butter does not have to be refrigerated, even after opening. So, if peanut butter is not a good home for bacteria, why is there a salmonella problem?
It seems when salmonella is mixed in as an ingredient, it causes a few more problems.
I saw on a local news broadcast that the peanut butter is contaminated with salmonella spores, which can survive roasting if the temperatures aren’t high enough. Peanut butter doesn’t have enough moisture for salmonella bacteria to grow, but when the spores come into contact with moisture (in the mouth or gut, for example), they come to life and start reproducing.
Peanut butter is just peanuts ground up, isn’t it? So if peanuts are safe unrefrigerated, then peanut butter should be too. I don’t anyone who keeps their peanuts in the refrigerator.
Look at a jar of peanut butter (at least most commercial brands) and you will see lots more things in there besides just peanuts. 
I cannot stand refrigerated peanut butter! It doesn’t spread properly and the taste is ruined. And that goes double for Pasteurized orange juice. Some of life’s pleasures are worth the risk of foodborne illness.
Bacteria cannot grow in peanut butter because there’s not enough water. Refrigeration is supposed to slow down or stop bacterial growth, so there’s no point in refrigerating peanut butter. The problem is that if the bacteria get into the stuff during manufacturing, it will still be there when you eat it. It doesn’t grow, but it doesn’t die, either.
Salmonella is not a spore-producing species. Bacillus and Clostridium species, maybe, but not Salmonella.
I use the peanuts-only, no preservative kind, and refrigerate it so it doesn’t separate or go rancid-tasting. I agree, it won’t spread when cold, so I dig out a few frigid chunks into a bowl and pop it in the microwave for twenty seconds or so. Works great.
I was just gonna ask about the peanut-only type.
If peanuts don’t go rancid, why would the “butter” made from them do so? Some molecular state of the oil once “extracted”? Or will shelled peanuts go rancid after a while?
Whole peanuts will indeed go rancid after awhile. Maybe they don’t stick around long enough for anyone to experience that very often! At least, in my house, they disappear within a day or two of my bringing them home. But I know I’ve eaten some old ones out of crappy vending machines in the past that tasted like cack.
I think it is easier for air to access the oils once it is ground up. Also, it separates leaving the oil on top. Like any other fat, air will oxidize it. You could probably get peanuts to go rancid if you deliberately left them out exposed to air in a warm area. It might take some time though.
Any nuts can and will eventually go rancid.
I had always thought it was the high sugar content which protected peanut butter from spoiling and that the natural ones that are just nuts had to be refrigerated.
I guess I’m unusual, but I actually prefer the taste of refrigerated peanut butter, probably because that’s what I grew up with. I find it odd that high sugar content inhibits bacteria growth. You would think bacteria would love sugar!
Too high a sugar concentration will kill bacteria via osmotic dehydration. I buy sugar free almond and peanut butters, but I suspect that even the commercial produced ones with sugar don’t have a high enough sugar content to kill bacteria. I figure it’s the lack of moisture that inhibits bacterial growth.
Rancidity is not a bacterial process, but an oxidative one.
Straight honey doesn’t grow bacteria because of its high sugar content. Honey in Pharonic tombs is evidently quite safe to eat - it never spoils.
I cannot believe there are people in this world who refrigerate normal, non-natural peanut butter. It boggles my little mind.
They do. It’s just that the sugar complexes with the water, making the water biologically unavailable. Add enough water, and the critters will quite happily eat up all that sugar.