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The common wisdom for storing prepared food for later is to store it in an airtight container and put it in the fridge, the temperature of which should be at or below 40 degrees Fahrenheit (4 degrees Celcius). I understand the purpose of the temperature is to slow the growth of bacteria to prolong the shelf life, but what about the airtight container? Is that also to slow bacteria growth, is it more about preservation of quality by preventing oxidation, or is it something else?

For the purposes of this question, I am more interested in the food I am storing itself, from a food safety and quality stand point. I get why you would want to store something pungent in an airtight container lest its odor get into any of your other items in the fridge or if you trying to prevent cross contamination between raw and cooked items. I simply would like to know what effect the airtight container has on the food itself vs. if I stored it in a non-airtight container.

Peter Mortensen
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anonandon
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    The inside of a fridge is quite dry (it's why they frost up; water in the fridge air condenses on the cooling plate, and then is ejected from the fridge separately) which can have a detrimental effect on moist foods that have been refrigerated – Caius Jard Aug 07 '20 at 11:11
  • @CaiusJard yep - it is possible to use a fridge as a dehydrator, if you cut the food thin enough and can expose top and bottom using some kind of rack. – Criggie Aug 07 '20 at 13:42
  • Is 4°C American? Fridges around here (Europe, Germany, etc.) run at about 7°C (~~ 45°F) by default, I think. – Martin Aug 08 '20 at 23:04
  • @Martin, here in Denmark usual and recommended fridge temperature is 5 deg Celsius (but my fridge can only be set to even temperatures, so I chose 4 deg.) – Stefan Aug 09 '20 at 08:00
  • A sealed container in a fridge will reduce the rate of dehydration. | Depending on the air volume present it may also reduce food oxidation - in some cases substantially. – Russell McMahon Aug 10 '20 at 11:39
  • Wait, fridges in Europe can be set by _temperature_!?! Admittedly I'm not exactly rocking high-tech appliances, but I've never in my life had or seen a fridge with any more precise temperature control than a "Cooling" dial that goes from Off to ...well, usually 9, oddly enough. Though I think my current fridge stops at 7 or 8. (Higher numbers == colder, so it's definitely not a temp control.) – FeRD Aug 24 '20 at 02:47

2 Answers2

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Airtight packaging doesn't slow down bacteria growth. There are a few myths about them which don't apply in practice:

  • Bacteria are not kept out, despite popular belief – the air within the container has as many bacteria as the air outside. The food in the container also has bacteria – cooking doesn't sterilize food! – so you cannot keep the bacteria out that way.
  • The container is still full of oxygen. You don't get the effect of lowered-oxygen atmosphere that is sometimes used in packaging from industrial food producers.

These two hold whether your food is in the fridge or not – so storing the food in an airtight container outside of the fridge doesn't change anything about its safety either. *

The one way it helps with food safety is an edge case: if you forget something until it molds or spoils, the now-high levels of pathogens won't contaminate something else, exposing it to more than the normal "background" level.

The airtight container doesn't help with food safety, but it is quite good for food quality and has other convenience aspects:

  • if you put fresh fruit or vegetables in it, or cheese, you get a nice level of humidity, and vegetables stay crisp longer/cheese and other stuff doesn't dry out
  • many foods either emit or soak up smells. The airtight container prevents it.
  • if you have a mishap and drop something in the fridge, or a fermenting bottle of something spills over, it won't land in an open bowl of something else
  • modern containers have an almost-rectangular shape, which uses up the space in the fridge very efficiently, and allows stacking.
  • modern containers, as well as humble jars, are mostly transparent – so if you store the food in them as opposed to the pot in which you prepared it, it is easier to see what is where without opening lids
  • if you prepared food in a reactive pan (or even something not-very-reactive like seasoned cast iron) and store the leftovers in it, you are giving the pan time to react with the food and corrode and/or change the taste of the food. Food storage containers are nonreactive.

So the airtight containers are best practice for quality reasons. And non-air-tight containers, which have a loosely fitting lid (no visible holes, but also no gasket, such as a stock pot or a skillet covered with a lid) will give you about 80-90% of the desired effect.

* to be pedantic, it can interfere in one way: if you intend to store hot non-shelf-stable food outside for a short time, and are afraid it will enter the danger zone, a closed lid will slow down the time it cools down. But I suppose not many people keep a wireless temperature probe in their airtight container, so the point is quite moot in practice.

Glorfindel
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rumtscho
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  • "The container is still full of oxygen." - What if you have an airtight container that also allows you to make a vacuum by removing the air inside? Would that create an "even safer" environment for the food? – GrumpyCrouton Aug 07 '20 at 12:09
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    @GrumpyCrouton it will reduce the growth of aerobic bacteria and increase the growth of anaerobic ones, especially raising the risk for botulism growth. So no, vacuum packing is not a viable way of food preservation at home. – rumtscho Aug 07 '20 at 12:18
  • Thanks for the quick response. So when you mention "lowered-oxygen atmosphere that is sometimes used in packaging from industrial food producers," how do they achieve this atmosphere and how does that differ from a vacuum? – GrumpyCrouton Aug 07 '20 at 12:21
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    @GrumpyCrouton They achieve the atmosphere by changing the ratio of oxygen to nitrogen, at least I believe that is what is typically done - they may be using some more specialized gas mixtures. It differs from vacuum, because they are filling the container (or the volume of it not occupied with food) with an atmosphere, while vaccum would be the absence of an atmosphere. – rumtscho Aug 07 '20 at 12:47
  • I fear you won't get much upvotes simply because majority of people don't know any better than to put stuff in containers or cover it up so "you can't possibly be right". I got a gf from another country and I'm not sure if it's the country, culture or maybe just her familiy, but she doesn't cover up stuff in the fridge and at first I was also kind of appaled by it but it really turned out to work just as fine. Although things do get drier much faster. – Ivo Aug 07 '20 at 14:37
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    "the air within the container has as many bacteria as the air outside" that will depend a lot on how clean you keep your fridge. Especially many molds like to grow there, so the amount of spores in fridge air could easily be higher than amount in the room air that gets put into the container. – jpa Aug 07 '20 at 15:12
  • @IvoBeckers I'm very much accustomed to 1) people's personal beliefs about food safety being based on wrong information and 2) people holding one to "the one true way of doing things" where there are multiple ways which work either alone or in combination (personally, I sometimes use sealed containers and sometimes don't bother). This doesn't stop me from writing answers which reflect the best of my knowledge :) – rumtscho Aug 07 '20 at 15:13
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    Yeah, cross-contamination with molds and other such bacteria between different foods is definitely an issue, and even if you get rid of moldy food, it would take some miracle to get rid of all the spores already scattered all over the fridge, so the container definitely helps with that - both ways, if you leave it too long and gets moldy it won't send its spores all over the fridge either. – SF. Aug 07 '20 at 15:14
  • @SF That doesn't necessarily require a strictly air tight container, though. I've definitely seen instances where a cardboard box or other fairly closed but definitely not airtight container contained mold. – user3067860 Aug 07 '20 at 17:29
  • @user3067860 The more it's airtight the lesser the chance the spores will get in. On the other hand, it's pretty rare to be able to tell authoritatively the food wasn't exposed to spores before being put in the packaging, so while this limits spread, it won't make your food magically mold-proof. – SF. Aug 07 '20 at 18:16
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    `cooking doesn't sterilize food` - I'll quibble with that [hardboiling eggs certainly sterilizes them, though odds are they don't remain sterile for nearly anyone after] - but otherwise a great answer. – Joe M Aug 07 '20 at 19:04
  • Additionally to all of this, certain foods will retain flavor longer in an airtight container due to not outgassing as much (because of the physics surrounding the concept of the equilibrium vapor pressure). This is especially true of raw freshly ground spices and foods which have a strong smell that's an important part of their flavor profile. – Austin Hemmelgarn Aug 07 '20 at 19:28
  • Another benefit for your list: efficiency. Cold air in the fridge flows out and is replaced by warm air whenever the door opens. Air in a container won't, so the fridge will operate (slightly) more efficiently and the food in the container will maintain a more even temperature. The more frequently the door is opened, the bigger the difference. – Robert Aug 07 '20 at 20:04
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    I don't disagree that an airtight container will contain oxygen, but it contains a finite amount. As the oxygen reacts with the food, the container will end up at a lower concentration of oxygen than it started, and therefore continued oxidation should slow down. Conversely, a container allowing air to flow freely will maintain a similar oxygen concentration the entire time even as it reacts with the food (as it has a larger volume of air to draw upon that regularly gets exchanged with the outside atmosphere). Thought experiment: how long would a candle burn in and out of a container? – fyrepenguin Aug 07 '20 at 20:49
  • @Robert Given the miniscule volume of air inside any given container, relative to the total free air volume inside of a typical fridge, I can't imagine any impact on efficiency would be significant enough that it's even *measurable*. Unless you're in the habit of packing your fridge with tightly-stacked airtight bricks, or something. – FeRD Aug 08 '20 at 00:20
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    @FeRD At present, ~20% of the volume of my fridge is occupied by airtight containers. Your fridge may be different. – Robert Aug 08 '20 at 05:28
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    "cooking doesn't sterilize food" I thought Clostridium botulinum is the only common harmful bacteria which (at least its spores) can survive 100°C? But since it’s sensitive to acid it still works fine for things like jam. So heating acidic food up to 100°C in an airtight container for a couple of minutes should preserve it quite nicely. – Michael Aug 08 '20 at 17:32
  • tldr; Use containers to control humidity and odours, also to save space. – J... Aug 09 '20 at 15:33
  • @fyrepenguin By the time the oxygen has gone down sufficiently to make any difference for anything, your food will be so rancid you wouldn't want to eat it. – rumtscho Aug 10 '20 at 10:39
  • @Michael sure, there are methods for preserving food by heating in a hermetic container - they are known under the common name "canning". Normally cooking a random meal, then placing it in an airtight container, is not a preservation method. – rumtscho Aug 10 '20 at 10:47
  • I see no mention of water/moisture loss. A sealed container in a fridge will reduce the rate of dehydration. – Russell McMahon Aug 10 '20 at 11:37
  • @RussellMcMahon it is the first point on my list of advantages - if it is unclearly written, feel free to suggest a better formulation. – rumtscho Aug 10 '20 at 11:48
  • @rumtscho are you sure about that? There are a number of foods that tend to oxidize relatively quickly (apples, guacamole, etc.) that I would expect that limiting the volume of available oxygen would significantly reduce the overall oxidation. I'm tempted to do an experiment now, with various fill levels of container (which will provide different starting quantities of oxygen) along with something not in a container and compare the relative stages of oxidation – fyrepenguin Aug 10 '20 at 20:12
  • @fyrepenguin you seem to think that there is so little oxygen in the container that it will be "used up" before the phenoles in your apple are used up. I am pretty certain that this is not the case - first, you won't be able to reduce the oxygen content enough to make a difference, it doesn't matter if you have 21% or 20.5%, second the reaction is not actually limited by the presence of oxygen but by the presence of free enzymes, and third, the process you are hoping will use your oxygen is the one you want to prevent in the first place. – rumtscho Aug 10 '20 at 21:28
  • @rumtscho Nah - that's OK - I must be getting blinder than I thought in my old age :-). – Russell McMahon Aug 11 '20 at 05:14
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In addition to keeping odors contained and limiting the possibility of cross-contamination, oxygen degrades the quality of food. Oxygen also supports aerobic spoilage organisms. So, limiting air keeps your food fresher longer. Sealing up your food also limits dehydration. These containers are beneficial for both quality and safety.

moscafj
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