Why don’t ketchup, mustard, and peanut butter need refridgeration? Unless I missed something, all three are made from organic matter. Are they so packed with preservatives that they have a longer half-life than nuclear waste? What gives?
- Adam
Here in the Munch household we (and by “we” I of course mean “I”) refridgerate the ketchup and mustard. Never seen it any other way, in fact.
But that’s a good point about the peanut butter. Weird.
Obviously you didn’t grow up in the deep South without air-conditioning. The trm is “rancid.”
Even with air conditioning, I once left a half-used jar of spaghetti sauce in my cupboard for a few days. When I opened it back up, there was an entire colony living in there.
I suspect you just use the products up before bad stuff happens.
I would guess that they do have a lot of preservatives, but a lot depends on how fast you use up said goodies. I go through one bottle of ketchup a year, so that goes in the fridge once opened. Mustard goes a little faster, but still, in the fridge it goes. PB, on the other hand, doesn’t last a full week per jar and it’s all yicky to spread ice-cold PB on Wonderbread, so it stays in the cabinet. I can’t check right now, but I think it says"refrigerate after opening" somewhere on the label in really small letters. I think.YMMV
Well, I just checked in the fridge, and the mustard says “refrigerate after opening”, but the ketchup doesn’t say anything about it. We don’t have any PB.
Unfortunately, I can’t answer your question.
Ketchup should have enough vinegar to pickle the contents - similar to the idea of having pickled vegetables for preserving.
Peanut butter has enough oil to preserve it through water exclusion. Same idea as a bottle of peppers/sundried tomatos in oil. Incidentally, the same principle applies to jams. By storing fruit in loads of sugar, you can preserve it.
The reason why kunilou’s spaghetti sauce went funky is because it doesn’t have enough preservatives to halt the grow of microbes. The watery solution makes for a nice microbial nursery.
I’m not too sure about mustard; I haven’t checked the ingredient list lately.
I don’t refrigerate ketchup or mustard and never have had either go bad on me. I do refrigerate speghetti sauce and have had that go bad. Dunno what the difference between speghetti and ketchup as far as why one goes bad and the other doesn’t.
Peanut butter contains so little water that microbes can’t survive in it.
Jelly/jam/preserves are loaded with sugar. You might think the abundance of sugar provides an ideal enviroment for microbes (lots of food), but there’s such a high concentration of sugar that it osmotically draws water from microbes, causing them to dehydrate and die.
The difference is that ketchup has a lot of sugar and vinegar, both of which are preservatives.
Ketchup contains vinegar. Spaghetti sauce, besides containing tomatoes, also contain perishable ingredients, such as meat, mushrooms, etc., but does not contain vinegar.
I would refrigerate PB, as if you don’t aflatoxin contents can increase. I would, if I ever bought any, but haven’t in many years. A good rule of thumb is to read the label. If it says refrigerate after opening, it would be a good idea for you to do so.
I also refrigerate my fruit preserves after opening and my olive oil after opening. Hey, it’s better to be on the safe side than sorry. Is your refrigerator so filled that there’s no room for a little bottle or jar?
From Heinz:
I buy the natural peanut butter, and that has to be refrigerated. It is peanuts and oil, no preservatives. Most normal peanut butter has preservatives to keep it fresh. It also has trans fats (that’s the reason I buy natural) and don’t trans fats also have a long shelf life? Isn’t trans fats the reason why Twinkies and stuff like that last forever?
I do refridgerate ketchup, mustard, and peanut butter – before and after opening. I find it kind of gross if they aren’t.
- Adam
UK Ketchup always says “refrigerate after opening”…and 99% of people don’t.
Dammit, don’t ask for a cite :rolleyes:
Isn’t anyone going to mention the M word (and start a holy war regarding the refrigeration of mayonnaise…)? 
No, trans fats do not increase the shelf life of food. If anything, they would decrease its shelf life.
Also, if the peanut butter is natural, it should not have any trans fats in it. If you read the ingredients, the only thing it should say is: peanuts. (If salt is added, then salt would also be on the list).
It’s un-natural peanut butter that contains trans fats.
Tomato sauce (ketchup) should be refridgerated because it makes for a better eating experience: hot chips + cold sauce… mmm!
People refrigerate peanut butter? I never even heard of that until tonight.
Bingo. This is called “water activity”. I have a degree in microbiology, so for once, I know what I’m talking about. Microbes require a fairly significant amount of free water to grow. In these products, most of the water is tied up in emulsions or hydrating sugars, leaving very little water for microbes to grow. Hostile pH and other factors also contribute, but water activity is extremely important.
This DOES apply to mayonaisse, too. As long as you don’t get foreign goop in your mayo, it does not need to be refrigerated. But if it gets mixed with some other food, like potatoes in potato salad or bread crumps from a dirty knife, there will be enough water around to allow nasty stuff to grow. And since mayo includes eggs, there’s a chance of Salmonella poisoning. So once you’ve opened and stuck a knife in your mayo, stick it back in the fridge.
Now, there are other ways for food to go bad besides microbial activity. Someone mentioned rancid peanut butter. Oils can go rancid through oxidation just through exposure to air. But bacteria and fungi have nothing to do with that process.
Peanut oil is liquid at room temperature. The oil in natural peanut butter tends to separate and float to the top. Refridgerating the peanut butter causes the oil to solidify and prevents separation. Most hydrogenated oils are solid at room temperature, so non-natural peanut butter doesn’t separate and doesn’t need refridgeration.
Peanut butter can become rancid. This type of spoilage is caused by oils and fats breaking down and oxidizing over time, not by bacterial action. Refridgeration delays the onset of rancidity.
Both mustard and ketchup contain a lot of vinegar - enough to prevent spoilage. Ketchup can separate, though, and refridgeration prevents this.
I have noticed that almost all packages of food now say to refridgerate after opening. I suppose the big companies’ big lawyers insist on it. One of these days I expect to see the instruction on a container of salt.