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User manuals of some freezers indicate that for the first few hours after switching on the new freezer, one should not put any food into it. For instance, I am looking at a specimen that requires me to wait for 6 hours before starting to fill it.

Note that this is unrelated to letting the freezer stand upright for a while before switching it on.

This rule is alluded to on various non-product-specific websites, as well. Two examples:

What is this restriction based upon?

If I put some frozen food (bought in a frozen state) into a new freezer right after switching it on for the first time, what could happen?

  • Is it bad for the food?
  • Is it bad for the freezer?
  • Is it bad for either of these no matter what, or only in specific circumstances?
  • Or is it one of those restrictions that are reiterated by many who do not actually remember what the rule was for and under what circumstances it was applicable?

UPDATE: Here are some clarifications, as the scope of this question appears to be unclear.

First, I am not asking for

  • what the restriction says
  • what might be a valid guideline if I ignore the restriction
  • how I might preserve frozen food during the initial period

I am truly looking for the technical rationale behind the restriction as stated.

  • 1
    Sorry, as pointed out in comments under the answer, two of your new subquestions are not compatible with interpreting food safety rules as objective criteria, so I had to remove them. – rumtscho Oct 6 '17 at 21:56
  • Maybe "subquestions" was a badly chosen term. The removed part seemed to me as if you invited answers to discuss what is a "lesser evil" and "cases in which the restriction does not apply", both of which would make your question subjective and thus closable. If you meant something else, you can try expressing it in a different way so that we can be certain that such discussion will not happen. – rumtscho Oct 6 '17 at 22:04
  • @rumtscho: "as if you invited answers to discuss what is a 'lesser evil'" - absolutely not. I want to decide that for myself, but for that, I need an accurate basis of information, which I was hoping to get by asking for the underlying rationale to the restriction. On the other hand, I still fail to see how asking for "cases in which the restriction does not apply" is subjective. As I already stated in one of the comments on the answer that were moved into the chat, the manufacturer's word is not automatically as accurate or true as you can get. – O. R. Mapper Oct 6 '17 at 22:07
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    What I've been trying to say in the long comment thread is: if you do not want to accept the manufacturer's word as true, your question is automatically off topic. – rumtscho Oct 6 '17 at 22:25
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    @O.R.Mapper To be clear, it's fine to ask why certain restrictions exist, which is roughly equivalent to what the consequences of ignoring them might be. And if you actually managed to find something totally unreasonable recommended by a manufacturer ("you must clean your freezer once a week with bleach!!"), asking for real safety guidelines would be a fair question. It's when you get into the business of replacing real guidelines with "homemade" ones that we veer into off-topic territory. – Cascabel Oct 6 '17 at 23:06
32

Most of the "cold" in a freezer isn't stored in the air. It's stored in the contents of the freezer, and in the walls (air has a very low volumetric specific heat). However, the thermostat controlling the compressor works off the air temperature.

If you start filling a freezer before it's had a chance to properly cool the walls down, the food is exposed to an effective temperature that is far higher than the freezer's setpoint: heat gets transferred from the walls to the food, warming it up to unsafe levels. Only once the walls reach thermal equilibrium with the air is it safe to start filling the freezer.

  • Same reason why you should not put too much at once into the freezer (unless it is at temp already) and can put more at once into it the more is already in there (at temp). Some people that use a lot freezers sometimes have a small one with a powerful compressor to cool things down and only then put it into the energy efficient ones – PlasmaHH Oct 7 '17 at 11:34
  • @PlasmaHH Or people put some water bottles in when a large delivery is expected, and remove the bottles couple hours after they put the new stuff in. – yo' Oct 7 '17 at 12:59
9

The mechanisms that cool the freezer work not by cooling the food directly, but by holding the temperature inside the freezer at a constant 0°F (-18°C). A freezer at any temperature above 0°F will not perform as expected, and will not keep food at the expected temperature.

A manufacturer's instruction booklet is intended specifically to ensure the product operates as expected. While undoubtedly safety and legal concerns are a factor in their instructions, the primary concern is simply instructing the user how to operate the device under expected operating conditions.

As such, a freezer includes instructions to bring it down to 0°F prior to placing any food in it, as that ensures the freezer operates under correct conditions.

The manufacturer does not include instructions for suboptimal operation, unless said suboptimal operation is an expected condition (such as instructing a driver how to operate their car in very hot or very cold weather). A user who wishes to operate the device under suboptimal conditions does so at their own discrection. This is in part due to legal/safety concerns, but the primary reason is that the manufacturer does not want to support said usage; if they included instructions in their manual for operating their device in a suboptimal fashion, they likely would field calls from users either wanting to know how to operate it, or frustrated buyers who have spoiled food because they operated it per the manual's instructions (even with warnings that it is suboptimal).

A freezer that is not at 0°F likely will still keep food "safe" to some extent, as the food "danger zone" is only above 40°F; likely less than 30 degrees below the beginning temperature of the room. Between that and the original temperature of the frozen food, it's unlikely that the frozen food would pass above 40°F unless it was very low in mass, and certainly not for several hours (as the freezer likely is below that temperature within an hour).

Food placed in the freezer immediately after the freezer was plugged in would very likely partially thaw, unless it had very high mass (for example, if you entirely filled the freezer with frozen goods), or a relatively high freezing point. Even then, some of the food would partially thaw on the outside (though this happens anyway in a automatic defrost freezer).

If the question is, however, "if I have frozen food, and nowhere else to store it, is it better to put it in the freezer than leave it outside," I would say that the freezer is undoubtedly your best choice. The food may or may not stay frozen - again, odds are it won't - but if it's food that can stand to thaw and refreeze without too much quality damage, it's probably going to be okay, and if there's no actual freezer option, that may be your best shot. It's not going to hurt the freezer, just the food. Just be aware that the food will probably thaw, might warm even into the danger zone for a bit, and take that into consideration. I would place a thermometer in the freezer to see the temperature of the freezer, and using a laser thermometer to temp the outside of the food, to ensure that it stays cold enough; and depending on how warm it gets, adjust the expiration date of the food down.

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    I think think the real question isn't "is better to put it in the freezer or not", but "please provide me with a rationalization that would justify my decision to not follow the manufacture's instructions". – Ross Ridge Oct 6 '17 at 22:41
  • @RossRidge: Basically, it was. I did not realize this site had a restriction against questioning manufacturer's instructions, like you'd normally do for products. Sorry for the confusion that rumtscho cleared up meanwhile in their comment. – O. R. Mapper Oct 6 '17 at 22:46
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It is a safety rule. Different freezers take different times to cool down the food placed in them, and the time depends among other things on the starting temperature within the freezer.

The manufacturer has determined that, if you start filling food before 6 hours have passed (and the freezer has cooled enough), the food has a chance of warming enough to enter the danger zone before the freezer can cool it. It is unclear if the assumption is that you are going to start filling frozen or room temperature food, so that if you want to follow the rule, you have to assume it applies to any food.

  • Comments moved to chat.stackexchange.com/rooms/66738/… – rumtscho Oct 6 '17 at 21:57
  • Most likely, there's a a specific test of cooling X food from above danger zone➞danger zone➞below it, which the freezer must pass.The design would be to meet the required test with the unit starting at cold-equilibrium. When starting at room temperature, the cooling mechanism must also cool all portions of the freezer (walls; interior cooling components; attached refrigerator, if any; etc.). Any freezer is rated at being able to move only X amount of energy/unit time. The extra time is what's calculated to be able to achieve that the cold-equilibrium state, prior to also cooling food. – Makyen Oct 6 '17 at 22:50
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    Thus, while warming enough to be in the danger zone is one scenario, it's likely the manufacturer has a many tests which must be met. What's clear is that the manufacturer is not guaranteeing the unit will operate as specified, unless there's been the initial cool-down period. As you've indicated, the main issue, from a user's point of view, is: is the food safe, which is largely: how long it's in the danger zone. The manufacturer will have a specific set of circumstances which will result in it being too long (e.g. putting too much hot food in the freezer). This is just one such circumstance. – Makyen Oct 6 '17 at 23:02

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