# Peanut butter: Refrigeration and salmonella **URL:** \ **Category:** Cafe Society\ **Created:** [January 23, 2009, 3:48am UTC](https://boards.straightdope.com/t/peanut-butter-refrigeration-and-salmonella/482574 "2009-01-23T03:48:22Z")\ **Posts on this page:** 19\ **Page:** 1
**Author:** ![DaveRaver](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/daveraver/32/1078_2.png) [@DaveRaver](https://boards.straightdope.com/u/DaveRaver)\ **Post date:** [January 23, 2009, 3:48am UTC](https://boards.straightdope.com/t/peanut-butter-refrigeration-and-salmonella/482574/1 "2009-01-23T03:48:22Z")
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? 😕 ---
**Author:** ![Boyo\_Jim](https://avatars.discourse-cdn.com/v4/letter/b/87869e/32.png) [@Boyo\_Jim](https://boards.straightdope.com/u/Boyo_Jim)\ **Post date:** [January 23, 2009, 6:07am UTC](https://boards.straightdope.com/t/peanut-butter-refrigeration-and-salmonella/482574/2 "2009-01-23T06:07:14Z")
It seems when salmonella is mixed in as an ingredient, it causes a few more problems. ---
**Author:** ![TWDuke](https://avatars.discourse-cdn.com/v4/letter/t/e495f1/32.png) [@TWDuke](https://boards.straightdope.com/u/TWDuke)\ **Post date:** [January 23, 2009, 6:33am UTC](https://boards.straightdope.com/t/peanut-butter-refrigeration-and-salmonella/482574/3 "2009-01-23T06:33:05Z")
[http://www.extension.iastate.edu/FoodSafety/peanutbutter.pdf](http://www.extension.iastate.edu/FoodSafety/peanutbutter.pdf) > [@](#): > > \*\*Why isn’t peanut butter refrigerated if it supports infectious bacteria? > \*\* > Peanut butter is shelf-stable and does not need refrigeration, although cool temperatures will make it last longer. The peanut butter itself does not support growth of harmful bacteria, as its low water content and high sugar content inhibit bacteria. Studies show the high fat content of peanut butter may protect bacteria from heat if already present. This recent outbreak of Salmonella in peanut butter is unprecedented, and is likely caused by an accidental contamination after the peanuts were roasted. The bacteria are present in the peanut butter but are not multiplying. Under normal circumstances, peanut butter does not need refrigeration to prevent spoilage. ---
**Author:** ![Jeff\_Lichtman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jeff_lichtman/32/1531_2.png) [@Jeff\_Lichtman](https://boards.straightdope.com/u/Jeff_Lichtman)\ **Post date:** [January 23, 2009, 8:13am UTC](https://boards.straightdope.com/t/peanut-butter-refrigeration-and-salmonella/482574/4 "2009-01-23T08:13:47Z")
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. ---
**Author:** ![guizot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/guizot/32/3636_2.png) [@guizot](https://boards.straightdope.com/u/guizot)\ **Post date:** [January 23, 2009, 11:34am UTC](https://boards.straightdope.com/t/peanut-butter-refrigeration-and-salmonella/482574/5 "2009-01-23T11:34:49Z")
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. ---
**Author:** ![DSYoungEsq](https://avatars.discourse-cdn.com/v4/letter/d/c6cbf5/32.png) [@DSYoungEsq](https://boards.straightdope.com/u/DSYoungEsq)\ **Post date:** [January 23, 2009, 12:02pm UTC](https://boards.straightdope.com/t/peanut-butter-refrigeration-and-salmonella/482574/6 "2009-01-23T12:02:07Z")
> [@guizot](#): > > 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. 😉 ---
**Author:** ![Horatio\_Hellpop](https://avatars.discourse-cdn.com/v4/letter/h/e5b9ba/32.png) [@Horatio\_Hellpop](https://boards.straightdope.com/u/Horatio_Hellpop)\ **Post date:** [January 23, 2009, 12:16pm UTC](https://boards.straightdope.com/t/peanut-butter-refrigeration-and-salmonella/482574/7 "2009-01-23T12:16:06Z")
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. ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [January 23, 2009, 2:03pm UTC](https://boards.straightdope.com/t/peanut-butter-refrigeration-and-salmonella/482574/8 "2009-01-23T14:03:31Z")
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. ---
**Author:** ![Antigen](https://avatars.discourse-cdn.com/v4/letter/a/848f3c/32.png) [@Antigen](https://boards.straightdope.com/u/Antigen)\ **Post date:** [January 23, 2009, 2:10pm UTC](https://boards.straightdope.com/t/peanut-butter-refrigeration-and-salmonella/482574/9 "2009-01-23T14:10:04Z")
> [@Jeff\_Lichtman](#): > > 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. _Salmonella_ is not a spore-producing species. _Bacillus_ and _Clostridium_ species, maybe, but not _Salmonella_. ---
**Author:** ![teela\_brown](https://avatars.discourse-cdn.com/v4/letter/t/d9b06d/32.png) [@teela\_brown](https://boards.straightdope.com/u/teela_brown)\ **Post date:** [January 23, 2009, 5:23pm UTC](https://boards.straightdope.com/t/peanut-butter-refrigeration-and-salmonella/482574/10 "2009-01-23T17:23:53Z")
> [@Krokodil](#): > > 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. 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. ---
**Author:** ![ThePylon](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@ThePylon](https://boards.straightdope.com/u/ThePylon)\ **Post date:** [January 23, 2009, 6:40pm UTC](https://boards.straightdope.com/t/peanut-butter-refrigeration-and-salmonella/482574/11 "2009-01-23T18:40:13Z")
> [@teela\_brown](#): > > 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? ---
**Author:** ![teela\_brown](https://avatars.discourse-cdn.com/v4/letter/t/d9b06d/32.png) [@teela\_brown](https://boards.straightdope.com/u/teela_brown)\ **Post date:** [January 23, 2009, 8:55pm UTC](https://boards.straightdope.com/t/peanut-butter-refrigeration-and-salmonella/482574/12 "2009-01-23T20:55:46Z")
> [@ThePylon](#): > > 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. ---
**Author:** ![WarmNPrickly](https://avatars.discourse-cdn.com/v4/letter/w/d78d45/32.png) [@WarmNPrickly](https://boards.straightdope.com/u/WarmNPrickly)\ **Post date:** [January 23, 2009, 8:57pm UTC](https://boards.straightdope.com/t/peanut-butter-refrigeration-and-salmonella/482574/13 "2009-01-23T20:57:30Z")
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. ---
**Author:** ![Zsofia](https://avatars.discourse-cdn.com/v4/letter/z/7bcc69/32.png) [@Zsofia](https://boards.straightdope.com/u/Zsofia)\ **Post date:** [January 23, 2009, 9:28pm UTC](https://boards.straightdope.com/t/peanut-butter-refrigeration-and-salmonella/482574/14 "2009-01-23T21:28:29Z")
Any nuts can and will eventually go rancid. ---
**Author:** ![kbear](https://avatars.discourse-cdn.com/v4/letter/k/4491bb/32.png) [@kbear](https://boards.straightdope.com/u/kbear)\ **Post date:** [January 23, 2009, 9:43pm UTC](https://boards.straightdope.com/t/peanut-butter-refrigeration-and-salmonella/482574/15 "2009-01-23T21:43:04Z")
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. ---
**Author:** ![DaveRaver](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/daveraver/32/1078_2.png) [@DaveRaver](https://boards.straightdope.com/u/DaveRaver)\ **Post date:** [January 24, 2009, 12:35am UTC](https://boards.straightdope.com/t/peanut-butter-refrigeration-and-salmonella/482574/16 "2009-01-24T00:35:24Z")
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! ---
**Author:** ![Bill\_Door](https://avatars.discourse-cdn.com/v4/letter/b/50afbb/32.png) [@Bill\_Door](https://boards.straightdope.com/u/Bill_Door)\ **Post date:** [January 24, 2009, 12:41am UTC](https://boards.straightdope.com/t/peanut-butter-refrigeration-and-salmonella/482574/17 "2009-01-24T00:41:03Z")
> [@DaveRaver](#): > > 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. ---
**Author:** ![Zsofia](https://avatars.discourse-cdn.com/v4/letter/z/7bcc69/32.png) [@Zsofia](https://boards.straightdope.com/u/Zsofia)\ **Post date:** [January 24, 2009, 2:09am UTC](https://boards.straightdope.com/t/peanut-butter-refrigeration-and-salmonella/482574/18 "2009-01-24T02:09:56Z")
> [@DaveRaver](#): > > 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! 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. ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [January 24, 2009, 3:35am UTC](https://boards.straightdope.com/t/peanut-butter-refrigeration-and-salmonella/482574/19 "2009-01-24T03:35:46Z")
> [@DaveRaver](#): > > 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! 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.