# Why does peanut butte not have to be refrigerated? **URL:** \ **Category:** Factual Questions\ **Created:** [August 10, 2003, 12:39am UTC](https://boards.straightdope.com/t/why-does-peanut-butte-not-have-to-be-refrigerated/194113 "2003-08-10T00:39:19Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [August 10, 2003, 1:53pm UTC](https://boards.straightdope.com/t/why-does-peanut-butte-not-have-to-be-refrigerated/194113/21 "2003-08-10T13:53:46Z")
> [@](#): > > And yet you eat Vegemite? I like Vegemite. _And_ I like peanut butter. But I’ve never tried them together. ---
**Author:** ![drhess](https://avatars.discourse-cdn.com/v4/letter/d/94ad74/32.png) [@drhess](https://boards.straightdope.com/u/drhess)\ **Post date:** [August 10, 2003, 1:57pm UTC](https://boards.straightdope.com/t/why-does-peanut-butte-not-have-to-be-refrigerated/194113/22 "2003-08-10T13:57:56Z")
Does high salt content in PB and/or other foods decrease bacteria growth? Are do they not care? ---
**Author:** ![wolfstu](https://avatars.discourse-cdn.com/v4/letter/w/d6d6ee/32.png) [@wolfstu](https://boards.straightdope.com/u/wolfstu)\ **Post date:** [August 10, 2003, 2:04pm UTC](https://boards.straightdope.com/t/why-does-peanut-butte-not-have-to-be-refrigerated/194113/23 "2003-08-10T14:04:10Z")
> [@](#): > > \*Originally posted by jovan \* > \*\*Try telling that to a Canadian! \*\* Oh, please. The oil is always on about how it’s being smothered by the peanut mash and salt. How it needs to get away from it to preserve its identity. ‘Distinct Society’, and all that jazz. Frankly, if the peanut butter is divisible, so is the oil. I’m sure there are components of the oil that would be plenty happy staying in the peanut butter, instead of pulling away into two solitudes that only really tasted good when they were together. 😃 (I _am_ one, **jovan**. And I’m starting to think that as a francophone in Japan, maybe you are too.) ---
**Author:** ![wolfstu](https://avatars.discourse-cdn.com/v4/letter/w/d6d6ee/32.png) [@wolfstu](https://boards.straightdope.com/u/wolfstu)\ **Post date:** [August 10, 2003, 2:09pm UTC](https://boards.straightdope.com/t/why-does-peanut-butte-not-have-to-be-refrigerated/194113/24 "2003-08-10T14:09:55Z")
> [@](#): > > \*Originally posted by drhess \* > \*\*Does high salt content in PB and/or other foods decrease bacteria growth? Are do they not care? \*\* If you put a bacterium in a solution of water and salt, osmosis will kill it if the salt concentration is too high. All the water inside the bacterium diffuses out into the salty-solution environment to try to even out the concentration of salt inside and outside the bacterium. Thing is, in PB, the concentration of water is so extremely low, the bacteria would never stand a chance. It needs water to do basic cellular stuff, and there isn’t enough to allow it to do that. And if there was, yeah, I’d guess the salt would kill it (by the osmosis mechanism, if not others). ---
**Author:** ![handy](https://avatars.discourse-cdn.com/v4/letter/h/b5a626/32.png) [@handy](https://boards.straightdope.com/u/handy)\ **Post date:** [August 10, 2003, 2:11pm UTC](https://boards.straightdope.com/t/why-does-peanut-butte-not-have-to-be-refrigerated/194113/25 "2003-08-10T14:11:48Z")
Peanuts don’t need to be refrigerated so why would peanut butter need it? ---
**Author:** ![wolfstu](https://avatars.discourse-cdn.com/v4/letter/w/d6d6ee/32.png) [@wolfstu](https://boards.straightdope.com/u/wolfstu)\ **Post date:** [August 10, 2003, 2:19pm UTC](https://boards.straightdope.com/t/why-does-peanut-butte-not-have-to-be-refrigerated/194113/26 "2003-08-10T14:19:48Z")
> [@](#): > > \*Originally posted by handy \* > \*\*Peanuts don’t need to be refrigerated so why would peanut butter need it? \*\* Tomatoes don’t need to be refrigerated, so why would ketchup? Apples… applesauce Mustard seeds… prepared mustard. Cows… ground beef. The way stuff comes in nature, it’s usally well gaurded against infection and rotting. Once you mash biomatter up and destroy its structure, it’s pretty much a highly nutritious growth medium. Which is why we eat it. And why bacteria eat it. Refrigerating slows down the bacteria. So do cellular membranes, immune systems, skin, and other things that were intact on food organisms befroe we cut them, sliced them, mashed them and mixed them up. ---
**Author:** ![Bren\_Cameron\_1](https://avatars.discourse-cdn.com/v4/letter/b/7bcc69/32.png) [@Bren\_Cameron\_1](https://boards.straightdope.com/u/Bren_Cameron_1)\ **Post date:** [August 10, 2003, 2:48pm UTC](https://boards.straightdope.com/t/why-does-peanut-butte-not-have-to-be-refrigerated/194113/27 "2003-08-10T14:48:12Z")
> [@](#): > > \*Originally posted by wolfstu \* > \*\*If you put a bacterium in a solution of water and salt, osmosis will kill it if the salt concentration is too high. All the water inside the bacterium diffuses out into the salty-solution environment to try to even out the concentration of salt inside and outside the bacterium. > > Thing is, in PB, the concentration of water is so extremely low, the bacteria would never stand a chance. It needs water to do basic cellular stuff, and there isn’t enough to allow it to do that. And if there was, yeah, I’d guess the salt would kill it (by the osmosis mechanism, if not others). \*\* The PB I get from the health food store has no salt in it. Also–this isn’t an argument, exactly, since I’m sure enough salt does kill cells, but childhood memory tells me osmotic upshock doesn’t always kill cells but rather makes them “non-colony producing units.” And those can sometimes be revived–they were, in my parents’ lab, and I heard about it over dinner. I went googling for the paper(s) and found one that mentions it (woohoo, my parents are cite 14), much of which is over my head. [http://sites.huji.ac.il/applsci/es/belkin/15.pdf](http://sites.huji.ac.il/applsci/es/belkin/15.pdf) Anyway, my (somewhat pointless) point is that sometimes the salt doesn’t kill the cells, it just shuts them down. (Yeah, I know, they won’t make you sick either way. I only mention it because **wolfstu** ’s post brought that whole set of memories back.) ---
**Author:** ![wolfstu](https://avatars.discourse-cdn.com/v4/letter/w/d6d6ee/32.png) [@wolfstu](https://boards.straightdope.com/u/wolfstu)\ **Post date:** [August 10, 2003, 5:17pm UTC](https://boards.straightdope.com/t/why-does-peanut-butte-not-have-to-be-refrigerated/194113/28 "2003-08-10T17:17:46Z")
> [@](#): > > \*Originally posted by Bren\_Cameron \* > \*\* Anyway, my (somewhat pointless) point is that sometimes the salt doesn’t kill the cells, it just shuts them down. \*\* Well, you’re probably right. I was just going by memory from biology class. And there, our discussion was of why a cell can’t survive in distilled water – because the much higher concentration of salts and other things inside the cell, compared to in distilled water, causes water to osmote into the cell until the membrane bursts. Whatever the case, you’re probalby right that a cell may not be killed, but if its rendered inactive, well, like you say, maybe that’s enough. Good point to make, though. In the fight against ignorance, nitpicks seal the chinks in the armour. ---
**Author:** ![Bob55](https://avatars.discourse-cdn.com/v4/letter/b/e9c0ed/32.png) [@Bob55](https://boards.straightdope.com/u/Bob55)\ **Post date:** [August 10, 2003, 7:07pm UTC](https://boards.straightdope.com/t/why-does-peanut-butte-not-have-to-be-refrigerated/194113/29 "2003-08-10T19:07:20Z")
> [@](#): > > \*Originally posted by wolfstu \* > \*\*Cite: umm… well, I work in the place where they make Reese Peanut Butter Cups… does that count? \*\* Mmmmm, Reese Peanut Butter Cups! That must be the best job ever. My wife sometimes wants TCBY, and there’s one 5 minutes from my house which rarely has any peaunut butter cups - I actually drive 10 minutes further to go to the TCBY that always has them! ---
**Author:** ![Llamer](https://avatars.discourse-cdn.com/v4/letter/l/eb9ed0/32.png) [@Llamer](https://boards.straightdope.com/u/Llamer)\ **Post date:** [August 10, 2003, 8:41pm UTC](https://boards.straightdope.com/t/why-does-peanut-butte-not-have-to-be-refrigerated/194113/30 "2003-08-10T20:41:39Z")
Actually, I was jjust informed as recently as this morning that there is a specific kind of fungus which grows on peanut butter. The best thing about it is that it is not visiable to the naked eye. Peanut butter can go bad, just as oil can go rancid, despite the lack of water within it. Don’t be fooled! ---
**Author:** ![wolfstu](https://avatars.discourse-cdn.com/v4/letter/w/d6d6ee/32.png) [@wolfstu](https://boards.straightdope.com/u/wolfstu)\ **Post date:** [August 10, 2003, 9:45pm UTC](https://boards.straightdope.com/t/why-does-peanut-butte-not-have-to-be-refrigerated/194113/31 "2003-08-10T21:45:14Z")
> [@](#): > > \*Originally posted by Bob55 \* > \*\*Mmmmm, Reese Peanut Butter Cups! That must be the best job ever. \*\* It’s tough, and it has its harrowing moments, but it’s all worth it in the end. You see, sometimes, I have to ‘rescue’ the cups that get lost in the complicated but ingenious conveyor system that takes them to the wrapping machines. They look so lonely and frightened, sitting there on the platform between the conveyor belts, unable to get themselves back on their way. They positively freeze in place with terror. They always thank me with a kiss. 😃 ---
**Author:** ![TheLoadedDog](https://avatars.discourse-cdn.com/v4/letter/t/35a633/32.png) [@TheLoadedDog](https://boards.straightdope.com/u/TheLoadedDog)\ **Post date:** [August 10, 2003, 9:52pm UTC](https://boards.straightdope.com/t/why-does-peanut-butte-not-have-to-be-refrigerated/194113/32 "2003-08-10T21:52:51Z")
> [@](#): > > \*Originally posted by astro \* > \*\*And yet you eat Vegemite? And don’t pretend that you don’t, I can sense you salivating at the mere mention of the word “vegemite” all the way on the other side of the planet. “Vegemite on toast. That’d be just the thing right now!” you’re saying to yourself. \*\* Hey, that’s not fair. Well, it _is_ 8am here and breakfast time… 'scuse me… 😃 ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [August 10, 2003, 10:00pm UTC](https://boards.straightdope.com/t/why-does-peanut-butte-not-have-to-be-refrigerated/194113/33 "2003-08-10T22:00:19Z")
> [@](#): > > \*Originally posted by Llamer \* > \*\*Actually, I was jjust informed as recently as this morning that there is a specific kind of fungus which grows on peanut butter. The best thing about it is that it is not visiable to the naked eye. Peanut butter can go bad, just as oil can go rancid, despite the lack of water within it. Don’t be fooled! \*\* Yes, there are a few fungi that are tough enough to grow on very low-moisture food, like peanut butter and honey, but they’re pretty rare. And most fungi will grow extensively before sprouting visible fruiting bodies. By the time you see mold on food, it will have already spread quite far through it. That why, with cheese, for instance, you should cut off a good chunk of seemingly good cheese along with the mold. ---
**Author:** ![Mister\_Rik](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mister_rik/32/491_2.png) [@Mister\_Rik](https://boards.straightdope.com/u/Mister_Rik)\ **Post date:** [August 10, 2003, 10:13pm UTC](https://boards.straightdope.com/t/why-does-peanut-butte-not-have-to-be-refrigerated/194113/34 "2003-08-10T22:13:16Z")
Also, bacteria need to breathe just like any other “animal”. And when you breathe through your “skin”, you’ll suffocate very quickly when you find yourself covered with oil. (It doesn’t take much to grease up a bacterium.) Some of the other foods mentioned above - like catsup and mustard - are highly acidic, which also inhibits bacterial growth. (Ya learn this stuff when you’ve worked in restaurants for 20 years.) I personally despise refrigerated peanut butter. I prefer my peanut butter to spread smoothly across my bread, not rip a hole in the middle of my bread because the lump is too stiff to spread. ---
**Author:** ![mangeorge](https://avatars.discourse-cdn.com/v4/letter/m/d78d45/32.png) [@mangeorge](https://boards.straightdope.com/u/mangeorge)\ **Post date:** [August 11, 2003, 1:11am UTC](https://boards.straightdope.com/t/why-does-peanut-butte-not-have-to-be-refrigerated/194113/35 "2003-08-11T01:11:41Z")
> [@](#): > > \*Originally posted by Phase42 \* > \*\*Also, bacteria need to breathe just like any other “animal”. And when you breathe through your “skin”, you’ll suffocate very quickly when you find yourself covered with oil. (It doesn’t take much to grease up a bacterium.) > > Some of the other foods mentioned above - like catsup and mustard - are highly acidic, which also inhibits bacterial growth. (Ya learn this stuff when you’ve worked in restaurants for 20 years.) > > I personally despise refrigerated peanut butter. I prefer my peanut butter to spread smoothly across my bread, not rip a hole in the middle of my bread because the lump is too stiff to spread. \*\* If you would use bread, instead of that fluffy stuff I won’t name but you have to wonder ;)😉 ))) ))) ))) what it is, you wouldn’t have the tearing problem. Actually, I know what you mean. If you leave the pb on the bread for a couple mins, it’ll soften. ---
**Author:** ![SmackFu](https://avatars.discourse-cdn.com/v4/letter/s/53a042/32.png) [@SmackFu](https://boards.straightdope.com/u/SmackFu)\ **Post date:** [August 11, 2003, 1:40pm UTC](https://boards.straightdope.com/t/why-does-peanut-butte-not-have-to-be-refrigerated/194113/36 "2003-08-11T13:40:41Z")
Since the original question seems to be answered, I’ll ask about another substance: why don’t you have to refrigerate (some) maple syrup? It has a high sugar content, and seems like an ideal place for bacteria to grow. ---
**Author:** ![Bren\_Cameron\_1](https://avatars.discourse-cdn.com/v4/letter/b/7bcc69/32.png) [@Bren\_Cameron\_1](https://boards.straightdope.com/u/Bren_Cameron_1)\ **Post date:** [August 11, 2003, 2:27pm UTC](https://boards.straightdope.com/t/why-does-peanut-butte-not-have-to-be-refrigerated/194113/37 "2003-08-11T14:27:31Z")
What my mother told me– Too much sugar is actually toxic for bacteria. Which is why you don’t have to worry about maple syrup. A quick google turns this up: [http://216.239.51.104/search?q=cache:YJsuyTbJLhsJ:newton.dep.anl.gov/askasci/mole00/mole00093.htm+sugar+preservative+bacteria&hl=en&ie=UTF-8](http://216.239.51.104/search?q=cache:YJsuyTbJLhsJ:newton.dep.anl.gov/askasci/mole00/mole00093.htm+sugar+preservative+bacteria&hl=en&ie=UTF-8) > [@](#): > > The major effect of salt as a preservative is that it withdraws water from microorganisms if the external salt concentration is high enough. The microbes would shrivel and die, spores would not be killed but would not be able to germinate. High concentrations of sugar have the same effect. ---
**Author:** ![derigel](https://avatars.discourse-cdn.com/v4/letter/d/839c29/32.png) [@derigel](https://boards.straightdope.com/u/derigel)\ **Post date:** [August 11, 2003, 4:55pm UTC](https://boards.straightdope.com/t/why-does-peanut-butte-not-have-to-be-refrigerated/194113/38 "2003-08-11T16:55:40Z")
> [@](#): > > \*Originally posted by Llamer \* > \*\*Actually, I was jjust informed as recently as this morning that there is a specific kind of fungus which grows on peanut butter. The best thing about it is that it is not visiable to the naked eye. Peanut butter can go bad, just as oil can go rancid, despite the lack of water within it. Don’t be fooled! \*\* Llamer, you may be thinking of aspergillis. I learned about this in bacteriology class during a lecture on food poisoning and the need for preservatives. I then went home and checked for preservatives in my jar of Jif. No preservatives, but it did have an phone number for comments or questions. Having just learned that aspergillis produces the potent carcinogen aflatoxin, I gave the number a try and asked how I could know the peanut butter I was eating was still safe. Big mistake. Let’s just say that if Jif’s screening process for peanuts is one tenth as lengthy and thorough as the description of said screening process, very little aspergillis gets through. And as long as you leave the lid on, apparently not much will settle in the jar and grow within a few months. But if it gets fuzzy or smells bad, it’s probably a good idea to pitch it and invest a couple of bucks in a new jar of peanut butter. ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [August 11, 2003, 5:24pm UTC](https://boards.straightdope.com/t/why-does-peanut-butte-not-have-to-be-refrigerated/194113/39 "2003-08-11T17:24:28Z")
> [@](#): > > \*Originally posted by Bren\_Cameron \* > \*\*What my mother told me– > > Too much sugar is actually toxic for bacteria. Which is why you don’t have to worry about maple syrup. > > A quick google turns this up: > > [http://216.239.51.104/search?q=cache:YJsuyTbJLhsJ:newton.dep.anl.gov/askasci/mole00/mole00093.htm+sugar+preservative+bacteria&hl=en&ie=UTF-8](http://216.239.51.104/search?q=cache:YJsuyTbJLhsJ:newton.dep.anl.gov/askasci/mole00/mole00093.htm+sugar+preservative+bacteria&hl=en&ie=UTF-8) \*\* Well, as your cite says, it’s not too much sugar that’s toxic, it’s the fact that high amounts of sugar sequester the water away, so it’s not avaiable for the bacteria. Same as mayonnaise. Minor nitpick. ---
**Author:** ![Bren\_Cameron\_1](https://avatars.discourse-cdn.com/v4/letter/b/7bcc69/32.png) [@Bren\_Cameron\_1](https://boards.straightdope.com/u/Bren_Cameron_1)\ **Post date:** [August 11, 2003, 5:52pm UTC](https://boards.straightdope.com/t/why-does-peanut-butte-not-have-to-be-refrigerated/194113/40 "2003-08-11T17:52:43Z")
> [@](#): > > Minor nitpick. And a good one it is. [Previous page](https://boards.straightdope.com/t/why-does-peanut-butte-not-have-to-be-refrigerated/194113.md?page=1)