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Old 08-09-2003, 08:39 PM
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Why does peanut butte not have to be refrigerated?

Why does peanut butter not have to be refrigerated and other foods like jelly have to be?
Old 08-09-2003, 08:43 PM
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The peanut butter I buy says to refrigerate after opening...
Old 08-09-2003, 08:45 PM
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Bacteria grow where there are water and food. Bacteria like to eat sugars.

Peanut butter is essentially ground peanuts, salt, and maybe some flavouring or oil. There's negligible water, and not enough sugar. The bactera can't grow.

Cite: umm.... well, I work in the place where they make Reese Peanut Butter Cups... does that count?
Old 08-09-2003, 08:46 PM
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It's got a pretty high oil content, which might have something to do with it. Then again, perhaps the bacteria share my belief that the stuff is just too revolting to touch.
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Old 08-09-2003, 08:47 PM
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Also, the jars are barriers against bacteria entering, except those times when the jar is open.
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Old 08-09-2003, 08:48 PM
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Peanut butter can be stored without refrigeration because it contains less than 1% moisture and therefore cannot support the growth of bacteria or molds. PDF cite
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Old 08-09-2003, 08:56 PM
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I guess I should specify... we were designing a transfer system for peanut butter a couple of weeks ago, and one of the thigns you always discuss in designing a transfer system for food is whether there's a risk of microbiological contamination ("Micro Issues"). In this case, the senior engineers notified me that the risk of this was very low, because, well, for the reasons I gave above. Bacteria very rarely grow in PB, because it's just ground peanuts and salt, with maybe a couple of extra things.

Now, some commercially available peanut butters have a lot more in them- they may be sweetened, or have chemical flavourings or whatever added in. (IMO, those are to Peanut Butter what 'Orange Drink' is to Orange Juice) For these, there may be more moisture, and more things that the bacteria can metabolize. Maybe that's why some recommend refrigeration. Or maybe the manufacturer is afraid that you'll get the stuff wet.

So, that's the story. In general, PB can't support bacteria becasue it has very little moisture, and some lack of the right nutrients for the bacteria. But mostly just no moisture.
Old 08-09-2003, 08:58 PM
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Quote:
Originally posted by Q.E.D.
Peanut butter can be stored without refrigeration because it contains less than 1% moisture and therefore cannot support the growth of bacteria or molds. PDF cite
Doesn't it also contain a preservative - or several? It doesn't spoil because of bacteria but it can sure get rancid as I learned to my dismay a year or so ago.
Old 08-09-2003, 09:27 PM
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Peanut butte? What's that, a mountain of peanut?
Old 08-09-2003, 09:36 PM
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Quote:
Originally posted by Jomo Mojo
Peanut butte? What's that, a mountain of peanut?
Yes -- related to the hill of beans which played such a vital role in world politics and Hollywood films.
Old 08-09-2003, 09:45 PM
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My PB needs refridgeration so it won't seperate. It has no additives. No sugar.
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Old 08-09-2003, 09:51 PM
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Quote:
Originally posted by mangeorge
My PB needs refridgeration so it won't seperate.
Oh, well, there's that.

But separation is no big deal. You can just mix it back together.
Old 08-09-2003, 09:59 PM
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Remixing is a big pain in the ...uh butte. Until a year or so ago, I bought it from a U-grind-it place (which has since closed, sadly) and I refrigerated it immediately and it never separated. Needless to say it had no sugar, no salt, no preservative.
Old 08-09-2003, 10:01 PM
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Quote:
Originally posted by TheLoadedDog
It's got a pretty high oil content, which might have something to do with it. Then again, perhaps the bacteria share my belief that the stuff is just too revolting to touch.
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.
Old 08-09-2003, 11:05 PM
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Regular grocery store peanut butter needs no refrigeration (like Peter Pan, Skippy, etc). The "natural" peanut butter you find in health food stores (no added sugar or anything) says "for best quality refrigerate to avoid separation". But I don't think it's a health thing.
Old 08-09-2003, 11:15 PM
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Most commercial peanut butters are NOT just peanut butter and salt. I am looking at two peanut butter jars, with the following ingredients:

1) peanuts, dextrose, partially hydrogenated vegetable oils, salt;

2) peanuts, sugar, dextrose, hydrogenated vegetable oil, salt, molasses, mono- and diglycerides.

Neither of these peanut butters contains antimicrobial preservatives; as others have explained, peanut butter does not have enough moisture to support bacterial growth (these do have enough sugar, I dare say). The presence of hydrogenated vegetable oils (fat, basically) and mono-and diglycerides (fat-related solids), however, explains why these do not need to be refrigerated, and "natural" peanut butter does: separation and rancidity.

Separation happens when the peanut solids "fall" through the liquid peanut oil. The above ingredients mix thoroughly with the oil and thicken it, preventing separation.

Rancidity happens when oil molecules oxidize; this happens far more easily to unsaturated oils (like peanut oil) than to saturated fats (like hydrogenated vegetable oil). Most peanut butter therefore takes more time to go rancid than "natural" peanut butter. Even the most "unnatural" peanut butter, however, will keep longer in the fridge.
Old 08-10-2003, 12:43 AM
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As a matter of fact, at least some manufacturers remove the peanut oil and replace it with other, more stable, oils.
Courtesy of "The Food Network", IIRC.
Old 08-10-2003, 03:25 AM
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Some people think it does - discussed here (amongst other things), tangentially here, by Jif here and by Skippy here.
Old 08-10-2003, 09:24 AM
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Quote:
Originally posted by wolfstu
But separation is no big deal.
Try telling that to a Canadian!
Old 08-10-2003, 09:26 AM
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Quote:
Originally posted by Hari Seldon
Remixing is a big pain in the ...uh butte. Until a year or so ago, I bought it from a U-grind-it place (which has since closed, sadly) and I refrigerated it immediately and it never separated. Needless to say it had no sugar, no salt, no preservative.

I've found that if I buy Smucker's Natural peanut butter (just ground peanuts) remixing is a pain in the neck. But--the stuff I get out of the grinder from the health food store never separates enough to need much more than a few swishes of the knife, and I never keep it in the refrigerator. I think the grocery store stuff sits on the shelf longer and gets solid or something.

I have a theory that if I ever managed to mix the grocery store stuff sufficiently, it would act like the health food store stuff, but since I really hate dealing with that solid lump of peanut under two inches of oil, I'm not going to try it until I can't get fresh ground anymore.
Old 08-10-2003, 09:53 AM
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Quote:
And yet you eat Vegemite?
I like Vegemite. And I like peanut butter. But I've never tried them together.
Old 08-10-2003, 09:57 AM
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Does high salt content in PB and/or other foods decrease bacteria growth? Are do they not care?
Old 08-10-2003, 10:04 AM
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Quote:
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.)
Old 08-10-2003, 10:09 AM
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Quote:
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).
Old 08-10-2003, 10:11 AM
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Peanuts don't need to be refrigerated so why would peanut butter need it?
Old 08-10-2003, 10:19 AM
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Quote:
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.
Old 08-10-2003, 10:48 AM
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Quote:
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

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.)
Old 08-10-2003, 01:17 PM
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Quote:
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.
Old 08-10-2003, 03:07 PM
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Quote:
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!
Old 08-10-2003, 04:41 PM
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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!
Old 08-10-2003, 05:45 PM
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Quote:
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.
Old 08-10-2003, 05:52 PM
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Quote:
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...

Old 08-10-2003, 06:00 PM
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Quote:
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.
Old 08-10-2003, 06:13 PM
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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.
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Old 08-10-2003, 09:11 PM
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Balloon bread, huh.

Quote:
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.
Old 08-11-2003, 09:40 AM
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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.
Old 08-11-2003, 10:27 AM
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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...hl=en&ie=UTF-8

Quote:
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.
Old 08-11-2003, 12:55 PM
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Quote:
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.
Old 08-11-2003, 01:24 PM
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Quote:
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...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.
Old 08-11-2003, 01:52 PM
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Quote:
Minor nitpick.
And a good one it is.
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