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I'm hoping this will solve a biiig long-running debate I have with my friends. Heinz Tomato Ketchup (The UK version contains sugar from beets, rather than HFCS like the US version)

I tend to think that ketchup should live in the fridge, once opened, because I'm a real stickler for the use-by instructions.

However, my friends, and their friends think I'm nuts, and are convinced that ketchup should live in the cupboard. Having eaten ketchup stored in both fridge, and cupboard, the only difference being that refrigerated ketchup also cools the food it's just been applied to.

Consensus of the cooking gurus then?

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At home I have always kept ketchup in the fridge after opening but now that I think of it, pretty much all restaurants that offer ketchup keep it on the table. And if you do ask for ketchup it is usually room temperature, implying it wasn't just pulled from the fridge. –  duchessofstokesay Feb 3 '11 at 23:45
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@duchess, as far as I know, restaurants also throw out their ketchup and other on-table condiments fairly frequently and refill from fresh bottles. At least, that was the practice at restaurants where I and my friends have worked. –  Pops Feb 4 '11 at 0:08
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It lasts longer in the fridge, if you are an infrequent user, but lasts a fair while in a cupboard. Also, IMO, condiments, particularly ketchup, are better served cold. –  Orbling Feb 4 '11 at 0:50
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I don't think it makes a huge amount of difference, especially as ketchup is loaded with sugar and vinegar and is generally well-sealed. The scientific thing to do would be to buy two cheap bottles of ketchup, open them, then leave one in the fridge and one in the cupboard and see which one lasts longer. –  ElendilTheTall Feb 4 '11 at 9:07
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@ElendilTheTall - But how do you tell when the ketchup is spoiled? –  Martin Beckett Feb 4 '11 at 16:35

1 Answer 1

up vote 10 down vote accepted

Anything can spoil eventually, refrigerated or not. Keeping something under a lid and refrigerated restricts the number of airborne colonizers that might get access to it, and the cold temperature means that even if they get there, they will grow much slower than at room temperature.

For something to spoil, it needs to be colonized by bacteria or fungus spores, and it needs to contain some nourishment to support their growth, not too much chemicals that prevent their growth, and not too much competing life forms already present. So, things with a high concentration of salt or sugar tend to be unhospitable to bacteria and fungi growth, because they are hygroscopic (they draw the water out of cells). Extreme high or low pH (eg acidic) also retards growth. Think of things like ketchup, mustard, jelly with labels that say "refrigerate after opening" but most people ignore them. Alcohol is unfriendly if the concentration is too high, and of course natural fermented foods are already occupied by human-friendly bacteria.

Ketchup is sealed in a bottle, usually with no fingers or utensils inserted into it, so it stays pretty sterile. It is also protected by being hygroscopic (due to high concentration of sugar and salt) and its acidity. Ketchup as a word and concept is descended from an Indonesian fish sauce, and has been around much longer than refrigeration. I think you can leave it out with no worries unless you see obvious mold growth.

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+1 "Ketchup is sealed in a bottle, usually with no fingers or utensils inserted into it" is the big clue - except when your little ones suck sauce directly from the bottle and contaminate the opening, even the fridge wont help then! But most people usually go through the stuff quickly enough that no one notices a little mould –  TFD Feb 6 '11 at 9:27

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