Peanuts Go In The Cupboard. Peanut Butter Goes in the Fridge. Why?
April 29, 2017 4:55 AM   Subscribe

I don't keep peanuts in the fridge, so why I am supposed to keep peanut butter in the fridge?

No matter the brand, the labels on the jars of the nothing-but-peanuts stuff I buy say "Refrigerate After Opening".

Why? What's the actual shelf life if I don't?

Most often these peanut butters are very thin and drip-off-a-knife liquid-y when first opened. Refrigeration thickens them to the consistency we expect to see in peanut butter. Are manufacturers increasing the amount of peanut oil in their products to meet a price point? Are they protecting themselves from consumers who'd leave an opened jar in the cupboard for months? Both
posted by justcorbly to Food & Drink (19 answers total) 1 user marked this as a favorite
Natural PB's are prone to separation (dry peanut lump at the bottom and oil on top). Refrigeration helps delay/prevent this from happening.

I lived in West Africa for 2 years and frequently bough quart sized containers of freshly ground PB and kept that out until it got used up (maybe a month?). It would always separate apart as I described above.
posted by raccoon409 at 5:01 AM on April 29, 2017 [8 favorites]

I don't keep peanut butter in the fridge, despite the label.
posted by fancyoats at 5:02 AM on April 29, 2017 [60 favorites]

I've never known about this. I've always kept peanut butter in the cabinet and it's always been delicious. As far as I'm concerned, it does not need to be refrigerated.
posted by blackzinfandel at 5:02 AM on April 29, 2017 [26 favorites]

Isn't natural PB also more prone to going off without refrigeration?
posted by Thorzdad at 5:04 AM on April 29, 2017 [1 favorite]

For what it's worth, I keep all my peanuts/nuts in the fridge or freezer - I buy them in large quantities and they go rancid otherwise. My guess is that ground up nuts would go rancid even faster.
posted by Knicke at 5:25 AM on April 29, 2017 [11 favorites]

I've never heard of keeping it in the fridge.
posted by blue_beetle at 5:28 AM on April 29, 2017 [6 favorites]

I think most "only peanuts" peanut butter says put in the fridge. The ones where they add stuff can usually be left out.

However, from what I've read, nuts keep best in the fridge. So I keep my peanuts in the fridge too.
posted by backwards guitar at 5:33 AM on April 29, 2017

I do the grinding machine peanut butter (literally just ground nuts) and never refrigerate it and have never had a problem. We do go through it fast though, less than a month usually.
posted by rabbitrabbit at 5:38 AM on April 29, 2017 [2 favorites]

I figured it was related to the problem of increasing surface area making things more prone to spoilage. Like grated cheese lasts less time than a block of cheese, coffee beans stay fresher longer as beans than when ground etc.

I find the natural ones much more liquid than ones with added fat and sugar so I prefer to refrigerate anyway to improve the consistency (I don't like the added ingredients even if they improve the texture for me).

I live in a hot climate but if I didn't, and I bought the non-natural peanut butter then I'd keep it in the cupboard. The natural stuff is more expensive, more gooey and my house is hot half the year, so it's best in the fridge.
posted by kitten magic at 5:40 AM on April 29, 2017 [6 favorites]

Keep it in the refrigerator to lengthen the time before it goes rancid. This never seems to be a problem at our house since the jar empties well before the use by date. We have been known to purchase in 35# buckets and never has it lasted long enough to go bad.

As to the "Why?"

Live Science says: Peanut butter is gooey and delicious, yet it can remain at room temperature for months without spoiling. Low moisture levels and high oil content keep this butter from going bad for quite some time, but don’t go ignoring that expiration date just yet. Peanut butter can go rancid in about a year and lose its flavor. While fungi and bacteria won’t ruin your peanut butter, oxygenation eventually will.
Label-lookers will notice that peanut butter is full of fat, sporting some 16 grams in a two-tablespoon serving. In addition to its natural peanut oil, peanut butters often contain other vegetable oils such as cottonseed, soybean and rapeseed. Since oil and water don’t mix, the more oil there is, the less room there is for water.
So despite feeling wet and greasy, peanut butter is actually extremely dry, with a moisture content of about 2 percent, according to Lydia Botham, the public affairs director for Land O’Lakes Inc. Without water, most bacteria and fungi can’t survive. Aridity is the chief way that peanut butter and other unrefrigerated comestibles, such as pasta and cereal, hold corruption at bay.
. . .The high fat content leaves PB vulnerable to a different type of food spoilage called rancidification.
Rancidification is a chemical process in which oxygen breaks down the molecular structures of lipids (the technical term for fats) and changes the flavor and odor of food in rather unappetizing ways. As peanut butter is exposed to more and more oxygen over its lifetime, it becomes likelier to undergo this decay. . . .
Rancidification typically sets in about nine to 12 months after purchase, hence the “Best If Used By” that appears on the container.
Health-wise, however, rancid peanut butter is not something to really worry about. “It won’t hurt you if you eat it — it will just taste bad,” says Maribeth Cousin, a professor of food science at Purdue University in Indiana.

and EatByDate says: How to tell if Peanut Butter is bad, rotten or spoiled?
Practicing proper hygiene and food safety techniques will help prevent foodborne illness.
Sight is usually the most reliable way to tell if your peanut butter has gone bad. A common trait of bad peanut butter is a change in texture from soft and creamy to hard and dry. The color of the spread may also become darker and the pleasant aroma disappears. If the peanut butter begins to smell rancid, toss it.
A natural separation of oil is natural, especially in the natural peanut butters that do not contain additional fats as stabilizers. . . . if oil begins to separate from processed peanut butter (Peter Pan, Jif, etc.) that is an indication that the peanut butter will soon be going bad.
How to store Peanut Butter to extend its shelf life?
You can help peanut butter keep fresh longer by storing it in your fridge immediately after use, although processed peanut butter will be fine on the shelf as well. Once prepared (if homemade) or opened from the jar, it should be stored in a tightly closed container. The original container works great to keep moisture and other contaminants from touching the peanut butter. Homemade and natural peanut butter should be kept in the refrigerator to last longer as they lack preservatives. Always use a clean utensil when using the product in order to avoid cross contamination.
Interesting facts about Peanut Butter:
It's a law in the United States that any product labeled "peanut butter" must contain at least 90% peanuts.
It takes about 540 peanuts to make a 12 ounce jar.
There is a name for the fear of having peanut butter stick to the roof of your mouth - arachibutyrophobia!
If you remember Mr Ed the talking horse (from TV), they gave the horse peanut butter to make his mouth move as if he was talking.

(Unopened) Refrigerator
Past Printed Date
Smooth Peanut Butter lasts for 1 Year
Crunchy Peanut Butter lasts for 1 Year
Natural Peanut Butter lasts for 3-6 Months
(Opened) Refrigerator
Homemade Peanut Butter lasts for 3-6 Months
Natural Peanut Butter lasts for 5-6 Months
Smooth Peanut Butter lasts for 6-8 Months
Crunchy Peanut Butter lasts for 6-8 Months

(Unopened) Pantry
Past Printed Date
Smooth Peanut Butter lasts for 1 Year
Crunchy Peanut Butter lasts for 1 Year
Natural Peanut Butter lasts for 2-3 Months
(Opened) Pantry
Smooth Peanut Butter lasts for 3-4 Months
Crunchy Peanut Butter lasts for 3-4 Months
posted by tronec at 6:18 AM on April 29, 2017 [14 favorites]

According to Harold McGee: The oils in nuts will tend to go rancid (and taste "stale") if exposed to oxygen and light. Walnut, pecans, cashews, and peanuts are especially susceptible to going stale. This process is accelerated by bruising, light, heat, and moisture, so it's best to keep nuts in opaque containers at cool temperatures; which basically means in the refrigerator or in the freezer.

The process of making nut butters ruptures a lot of the cells in the nut — it's basically "bruising" the nuts repeatedly until they fall apart — and so it stands to reason that nut butters are more susceptible to rancidity than are whole nuts. Roasted nuts are also more susceptible to rancidity than raw nuts, so if you're comparing raw peanuts to peanut butter (made from roasted peanuts, usually), the difference in rancidity time is probably even greater.

Oh, and peanut butter manufacturers are not adding oil to peanut butter; there really is that much oil in a peanut. By weight, a peanut is 6% water, 26% protein, 19% carbs, and 48% fat. (And peanuts are actually one of the less oily nuts; some types of nuts are over 70% fat.)
posted by Johnny Assay at 6:26 AM on April 29, 2017 [8 favorites]

I always assumed I had to keep the better, more natural PBs in the fridge, but I could keep the cheaper Kraft/Skippy PB's in the cupboard because of all the sugar, etc that helps keeps it from going off. I have no idea where I got that from. However I do strongly prefer cupboard-temp peanut butter.

That said - I can confirm even the cheap PB will eventually go rancid. It's not a pleasant experience.
posted by cgg at 6:50 AM on April 29, 2017 [2 favorites]

As noted above, eventually, the oils go off. But also, (as also noted above) I have a jar of the brand I buy (which is just peanuts and salt) at work and one at home. In home it's in the fridge but at work, it's not. The jar at home is a gooey, very-difficult-to-spread mess because it just won't stayed blended, unlike the jar I keep at home in the fridge.
posted by crush at 7:43 AM on April 29, 2017

I started refrigerating peanut butter years ago after a widely reported aflatoxin scare. Aflatoxins, produced by molds, cause liver damage and are associated with liver cancer. You can't detect them by taste. The idea is that refrigeration slows down the development of aflatoxins. The concern then was directed mainly toward peanut butter; I would guess that they must not develop as quickly in the solid peanuts.

The consensus now seems to be that peanuts and peanut butter sold in the United States are probably safe because of production practices in place, plus monitoring by the USDA and FDA, but aflatoxins remain a health problem in other parts of the world.

I still refrigerate peanut butter, both out of habit and because now I buy the kind you have to stir, and I'm too lazy to stir it more than once.
posted by hsieu at 8:55 AM on April 29, 2017 [4 favorites]

Ad an aside, I've found it's actually a pretty good idea to store nuts in the fridge. If you've ever bitten into a rancid peanut you'll agree.
posted by kapers at 9:47 AM on April 29, 2017 [2 favorites]

I keep all nuts in the fridge and peanut butter on the shelf. It sucks to spread natural peanut butter if it's been refrigerated.
posted by latkes at 10:30 AM on April 29, 2017

Also, manufacturers know you will put non-sterilized instruments into the jar repeatedly, maybe even instruments coated with a very sugary substance. Keeping it in the fridge helps slow down any spoiling that might introduce.

I always kept pb in the fridge; at some point when el_lupino was managing the kitchen while I was too sick to visit it, he started keeping it in the pantry. We buy the natural stuff, and I quit eating it until we stored it in the fridge again because if stored at room temperature, bitter flavors quickly overwhelm the roasty nut flavor for me.
posted by jocelmeow at 11:08 AM on April 29, 2017 [2 favorites]

I've never refrigerated peanut butter. I'm in my early 50s and so far have lived to tell the tale...
posted by bookmammal at 12:32 PM on April 29, 2017 [1 favorite]

In the winter, when the house is colder (we are adding insulation this year!) I leave it in the cupboard for spreadability. As it warms up, I start putting it in the fridge to keep it from separating so much. I keep almonds in a jar in the cupboard but walnuts in the fridge. Butter is in a covered dish in the cupboard. I've only once had it go bad when it was overheated and puddled.
posted by amanda at 1:37 PM on April 29, 2017

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