OT: Best Freezer Temperature.

Defrosting our upright freezer I discovered that, during the move, the

the time :-(

What's the best temperature to set it at? ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Jim Thompson
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-Lasse

Reply to
Lasse Langwadt Christensen

Freezer's are 0F, refrigerators are 32F.

Larger freezers (i.e., not the "freezer compartment" in a refrigerator) can be colder depending on what you are trying to store. Also note temperature striation effects (e.g., we store the most perishable items down in the bottom of our "chest" -- ditto with fresh citrus juices which seem to have a lower freezing temperature)

Reply to
Don Y

0F is too cold for a refrigerator, stuff in the back will freeze standard temperature is ~5'C or 41'F

-Lasse

Reply to
Lasse Langwadt Christensen

Freezer's are 0F, refrigerators are 32F. ^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^

Reply to
Don Y

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sorry, I meant 32F is too cold

-Lasse

Reply to
Lasse Langwadt Christensen

A lot depends on your refrigerator's design and controls. We don't have a fancy "digital temperature gauge" that we can just set to "32". We use a regular (frig) thermometer in the refrigerator and adjust the temperature "dial" until the thermometer reads 32F.

We don't see much variation from front to back to top to bottom of the refrigerator enclosure (well, we can't practically measure "just below the top of the box" as there's no easy way to leave the thermometer there -- perched atop the milk??)

We *do* notice ice cubes "shrinking" (evaporation/sublimation?) in the freezer compartment -- but never a puddle of water in the ice bin.

The freezer *chest* in the garage, however, has marked differences in temperatures between the top levels and bottom levels. I'm sure the exposure the top levels see to the warm outside air contributes to that -- much easier for cold air to escape the upper levels when the lid is raised than for the cold air to abandon the depths of the chest!

In power outages, we exploit this to quickly reorganize the placement of goods in the freezer to preserve those things most precious to us (who cares if we have to throw away some hamburg buns... OTOH, all the beef, fish, chicken and pork merit saving!)

Reply to
Don Y

Not unless you like wilted lettuce. 40F for me.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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Reply to
Phil Hobbs

On Sun, 23 Nov 2014 10:15:03 -0800 (PST), Lasse Langwadt Christensen Gave us:

You are full of it and or guessing again, as usual.

"standard food service", which is ALSO the standard for home

Reply to
DecadentLinuxUserNumeroUno

Den mandag den 24. november 2014 00.17.10 UTC+1 skrev DecadentLinuxUserNume roUno:

sure and that is says store at -18'C on everything you buy frozen is just to confuse

-Lasse

Reply to
Lasse Langwadt Christensen

Screw the lettuce! Above 40F the clock starts ticking for the "dispose of promptly": meat, dairy, fish/seafood, salads, anything labeled as "keep refrigerated", etc. need to be discarded at 2 hours above 40F. Do you really think your refrigerator *stays* at (or below) 40F when you target

40F? Door open? Power outage? The stuff on our *door* gets MUCH warmer than the 32F setting we maintain (pity the folks who store eggs, there!).

Sunday we make a pork meal. I have to wait until (my) bedtime (~3AM) before taking the pork tenderloin out of the freezer chest (which is at or below 0F) else it is *thawed* when sitting in the refrigerator for the few hours before SWMBO gets up and starts marinating it (for lunch). I.e., it doesn't take long for things inside the refrigerator to warm up -- even a few degrees (the block of pork rose 30+ degrees in those few hours).

Reply to
Don Y

On Sun, 23 Nov 2014 15:30:10 -0800 (PST), Lasse Langwadt Christensen Gave us:

Those are OPEN "display" freezers. a deep freeze chest (freezer) is supposed to rest at a considerably colder temp than what the stores achieve at gauge height. Sorry to break your ice cube.

Reply to
DecadentLinuxUserNumeroUno

I think he means the freezer part of the fridge, but then that seems too low. I believe they recommend that milk be stored no higher than 40

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Rick
Reply to
rickman

after 2 hours? Use a little common sense.

If you put the tenderloin in my fridge at 3AM it would be thawed by lunch the following day, not that same day... and even then it's a maybe.

Not sure what you are talking about with the "warming up". Most things

frozen to not frozen that takes a lot of heat and by that point the temperature difference is very small.

If a tenderloin defrosts in your fridge in some 6 or 8 hours, I would check the temperature. Are you talking about thin sliced meat or a solid roast?

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Rick
Reply to
rickman

I worked on gadgets for cryogenic storage of bio-samples.

Some important biological markers degrade quickly when warmed to -80C from LN2 temperatures (about -200C or 77K). -80C is warm enough for RFID electronics to start to be useful, which is a big part of the reason why bio-banks haven't adopted RFID tagging for samples.

Reply to
Clifford Heath

Yikes! What sorts of things?

Have NOT adopted? What am I missing? I.e., -80C is "too late" to be worth notification?

Hmmm... I just keep in mind that refrigeration doesn't "sterilize" the products you are trying to preserve but, rather, "slows their decay" (bacterial action). So, warm it up and things reproduce (increase in number); cool it back down and the number remains (largely) static... yet HIGHER than before you warmed it up! Lather, rinse, repeat each time the compressor cycles, door opens, etc.

IIRC, 40F is the "magic number" at which reproductive rates move the quality of the foodstuffs you are trying to preserve from "safe for several days" to "unsafe in several hours". Especially things like meat and dairy (meat being relatively expensive; dairy being a large part of my baked goods!)

The fact that all (?) refrigerators open like *doors* and let all the cold air "fall out the bottom (front)" has always seemed stupid to me. Contrast with freezer chests where opening has much smaller impact on the goods and air within.

E.g., when I defrost our freezer (which has an integral heating element to speed up the process), the bottom of the chest is still very cold even while the top sides are dripping from the melting ice (heationg element located up high in the sides). So, I have to mop up any liquid before it refreezes in the colder depths (or, let the entire freezer come up to room temperature)

Even the refrigerators with bottom freezers seem to have an "open basket" into which the frozen goods are placed. So, open the freezer and all that cold air falls right out the bottom of the basket! :-/

Reply to
Don Y

I didn't get into the biology much. Some samples for some purposes are ok stored at -80C, which is about the limit for normal heat-pumps. Those freezers tend to have front-opening doors. Typical biobank usage stores vials in 12x12, or 15x15 grids, in plastic or cardboard boxes. LN2 storage is in a dewar accessed from the top. You have to pull a full-depth rack to access the box or cartridge you need - so time is of the essence. Every time you pull a box for a single vial, the remainder get one warming cycle that lessens their usefulness.

Bar codes are widely used, both 2D and 3D, but suffer from immediate frosting that obscures the marks. Hand-written labels are hard to read when curled around 5mm diameter vials, and are especially useless when the adhesive fails due to the low temperatures. All the above have to be handled in massively thick cryogenic gloves, barely more suitable than boxing gloves, and even then you need a break after ten minutes, or you wind up with frostbite.

This is why labs make mistakes, and the wrong people get convicted, charged child support, or diagnosed and treated for someone else's cancer.

That's why I like

formatting link
's solution - it's based on mechanical resonance - the world's smallest electric guitar, with more than 50 resonators in a vacuum cavity inside a 1mm^3 chip, attached to a

5mm square antenna. The reader measures micro-ohms of RF impedance spectrum from 1 to 5MHz, across a transformer coupling. I hope they get the market adoption they deserve after ten years of development.

For some purposes, yes. For others, there are RFID solutions, but not widely adopted yet.

Like all rules-of-thumb, it's a pretty coarse approximation. Another says that reaction rates double every 10C.

The thermal mass of the air is very much less than the thermal mass of the contents and the walls. You probably lose less than 1% of the coolth each time you open it. Do the math based on mass approximations. I did it once for our house, to work how many times I needed to change the air to cool down, after the whole house got warmed up on a hot day. Changing the air once doesn't have much effect on the wall temperature.

Clifford Heath.

Reply to
Clifford Heath

the number above which food will start to decay faster. But there is no

*magic* number and it is not black and white. The higher the temperature the faster the degradation, both loss of nutrients and the multiplication of bacteria. But the process doesn't go into full speed

That's because 99.99% of people would not buy a chest type refrigerator due to it's inconvenience. Even in professional kitchens and laboratories the refrigerators are usually upright units while freezers (much colder air) are chests.

Yep, because to cool down quickly the things you add to the freezer, the drawer needs to allow ventilation. They spend a lot more time closed trying to cool the stuff than they do with the doors open. Air is easy to cool, food not so much.

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Rick
Reply to
rickman

Seems like it would be most prudent to have a "cheat sheet"/index that lets you figure out which vial you want *before* you open the door. And, ensure that index remains accurate and up-to-date. Pull the box, retrieve the vial, replace the box of OTHER samples... THEN, verify that your index isn't hosed!

Clever! Sealed away to be (reasonably) impervious to temperature extremes, moisture, etc.

When I designed the temperature alarm for the freezer, I researched this. No "pretty charts" saying "X minutes at Y degrees for product Z" -- which was what I had expected (I can then just accumulate current conditions and predict when things were going to fall apart).

Instead, I found "2 hours above 40F, discard". Not 2:30 above 40F... or 2 hours above 43F... or 3 hours above 38F...

Someone creating that rule of thumb looked at the likely pathogens found in our food supply and decided that specific time and that specific temperature were "right". They could have said "8 hours above 35 degrees". Or, "35 minutes above 50 degrees". But, they chose 2 hours (not 2:30) and 40 degrees. Presumably for some scientific reason looking at the growth rates of different pathogens in those temperature ranges, likelihood of a prolonged power outage, etc.

(I'm going to assume the folks who come up with these rules are *somewhat* competent and not engaged in some massive conspiracy to sell produce!)

If you've got your refrigerator AT 40F (let's assume it is consistent throughout the entire refrigerator *and* the sense point is not in some silly place -- like adjacent to the coils! :> ), then you've no room to spare if there's an outage, your kids leave the door open, or put some warm 2L bottles of soda inside in preparation for tonight's party, etc.

At 32F, food will keep (almost) indefinitely (though can still "develop bad tastes"). And, you have some wiggle room when you throw hot/warm leftovers in the refrigerator without cooling them, first.

The way most people use their refrigerators would be prohibited in a commercial setting. And, consumer refrigerators wouldn't be acceptable in those settings because they can't cool quickly, etc.

I'll dig through my notes and see what references I kept... but the 40F sticks out in my memory!

This also works in reverse. Put something room temperature (or, worse, *hot*) into the 40F refrigerator and see how long that item's internal temperature remains above 41F. Yet, this is exactly how people use the refrigerator: "Gee, this is WARM and I want it to be COLD... let's have the refrigerator move those BTU's..."

E.g., when I make marinara sauce, it's a real challenge to cool it to a "safe" temperature before throwing it into the refrigerator (where its sheer mass -- 16qt -- would RAISE the internal temperature of the nearby foodstuffs in the refrigerator). Even my lasagna takes 3 hours to cool to "refrigerator temperature" *if* cooled in the refrigerator (and, all that time, things are multiplying inside it as it is no longer TOO HOT for them).

Instead, I cool things in an ice water bath to get their internal temps down to a point where things aren't reproducing wildly -- and, where they won't heat up the other items in the refrigerator when introduced.

Likewise, when we defrost many things, its done in the refrigerator *in* a cold water bath (never on the counter due to the time required and the temperature to which it is exposed for that time). So the item can absorb heat from the surrounding water instead of hoping to warm up in free air.

Reply to
Don Y

At the reccomended temp for your intended content.

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Jasen Betts

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