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Old 03-01-2007, 13:20   #1
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Freezer Temperatures

It's winter. I have no idea why I have so many questions...

Here's another though:

The USDA suggests keeping your refrigerator below 40 deg F. Of course you want to keep it above 32F too, since frozen milk and veggies are not very fun.

My question has to do with the freezer. The USDA suggests a freezer temperature of 0 deg. No range at all, but a temerature of 0 deg F. My freezer can only go as low as 15F, and sometimes creeps up toward 30F. Everything stays frozen solid and is very cold.

Do any people who understand food safety and biology know what happens to the food at temperatures that are below freezing but above 0 deg F? Can any bacteria grow? Just off colors and flavors? Any danger? Is it just to make things last longer in terms of flavor?

If something is frozen, it seems that most organisms would have trouble growing owing to the fact that there is no liquid water available. Also, why does the USDA suggest 0, instead of say 15 or -15?

I guess I have a lot of questions because it *is* winter and I'm not out sailing.
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Old 03-01-2007, 13:33   #2
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Obviously, the USDA is the capitalist tool of the US Dairy Farmers' Association and we ALL know that ice cream won't freeze and keep properly at 30F, you need to get it down under 5F.

Would the USDA need any more logic than that?<G>


Ah, seriously though? If your freezer is at 30F or 25F and you throw in a fresh batch of leftovers or groceries, the stuff near them will melt and refreeze, allowing growth and harming texture from the ice crystals reforming. One stuff is frozen and stays frozen--the critters don't grow, they're just suspended. (Not killed until you get them way colder.)
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Old 03-01-2007, 13:54   #3
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Clemson University has some data on this at Food Storage: Refrigerator and Freezer

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Old 03-01-2007, 14:35   #4
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I have been in the food production/warehousing industry for most of my life. Proper freezer settings for different products is esential to the quality of the product. Ice Cream and things like that need to be -15 or lower, most of our meats can be kept arount -10. Ice crystals form in some products causing lower quality if the temp is not correct. Most freezers in your home can't get much below 0 unless you get a real nice high end model. If you can keep your freezer at +10 or better you will be fine unless you are storing for long periods, you will notice reduced quality over time if you cant maintain at least that temp

Hope that helped some
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Old 03-01-2007, 14:43   #5
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That does help, Mike. Thanks. I'm really curious if there are any food safety issues related to keeping food (meats mostly) at 30 degrees. We store fresh ground venison in our freezer (I am talking boat freezers here) which can only get to 15F min. It fluctuates between 15F and 30F (when it's time to run it).

I do notice that I can't store food as long as I could in a home freezer... ground meat gets a little more brownish colored, but lasts a month or two without killing us.
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Old 03-01-2007, 14:46   #6
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I have had the same questions and have found the answers in my freezer..?

To keep ice cream good and hard, ya need 0 F, (-18C).
For short term frozen meats and breads, I leave the freezer temp around 15F.
It is still plenty cold and below freezing, and should be safe enough for up to 4 weeks for stuff like beef and chicken. ( a month is my present cruising limit anyway)

The problem with keepin the freezer at 0 F is obviously the energy required: In my case, I need to run the compressor around 16 to 18 hours per day @ 5.3 AH =
90 AH just for the hard ice cream.
To keep 15 F, the running time is around 11 hours = 60 AH.

For keeping just ice cubes and frozen bread and such, I go even warmer 25 F and now the compressor running time is right around 6 hours, = 32 AH.

With the boat docked and with no use or abuse of the fridge and freezer, it will run about 3 hours per day for a total consumption of 15 to 18 AH at the lowest setting.(Highest temp)

So, uh to sum it up: Mama loves hard ice cream, and to keep mama happy, I sometimes load up with Ben&Jerry's and hope for lots of sun to keep the solar panels busy and the freezer right at 0 F..
Once the ice cream is consumed, I adjust the thermostat to keep around 15 F or so.
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Old 03-01-2007, 14:53   #7
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Sean, now I'm jealous. I knew a Gulfstar was commodious but dang, having so much room you can go deerhunting aboard it! <VBG>
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Old 03-01-2007, 15:11   #8
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Ha ha ha!! That's funny HelloSailor.

No, we are not keeping full deer in there. We buy a shoulder and some tenderloin (farm raised) while we're here in Jersey. Not much hunting around here that wouldn't get you shot by the over-zealous cops. We grind up the shoulder to make ground venison and keep steaks in the freezer as well. Because we buy weird stuff, we buy it in quantity and freeze it since we have to go way out of our way to get it.

When we move up to Maine, I plan on doing more hunting again and freezing things. Not sure what I could do with a deer though. I don't want to kill the thing if I can't use all the meat. Assuming I get one, maybe another person will want to take most of the meat? Eh... logistics.

In all reality, I'll probably cold pack and pressure can half a deer at least if I get one once we're in Maine.
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Old 03-01-2007, 16:21   #9
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I do not remember where I found it, but there is a chart for reletive food storage time by freezer temp. Extended meat storage requires sub zero. Zero defrees allows for a moderate storage time. 32 degrees was listed for a couple of weeks for meat storage if I recall. Sorry I can not remeber the source right now, but I will look for it. Like most things, it is a compromise. Unless you want to spend more in referigeration than the cost of the food, short time storage is the only real option. My opinion, FWIW, is that referigeration should be minimal, even limited to an ice box, but freezer space should be a priority. The logic has to do with food longevity. Most foods that are stored at 40 degrees will only last a week or two at the most. Freezer foods, much longer. A freezer can also make ice to keep an ice box cold. Build a good freezer, and use an ice box, and you will get the most for your dollar, and space.
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Old 03-01-2007, 16:24   #10
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Agreed, Kai Nui. We purposefully upgraded our refrigeration system just so we could have a large freezer.
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Old 03-01-2007, 17:03   #11
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And yet, no one is making a good, efficient marine freezer. Norcold and the like ar making 5 or 6 cu ft refers with a tiny freezers.
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Old 03-01-2007, 17:14   #12
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Not trying to be annoying, but:

I'm not so sure... no manufacturer is making a good freezer box and compressor, but installing a marine refrigeration system properly seems to work well.

My freezer seems pretty reasonable for our uses. It is a 1/2HP 120VAC Tecnicold compressor with an (estimated) 3ftx2ftx4inch holding plate. Keeps everything frozen to 15deg (because the solution in the holding plate is mixed to freeze somewhere between 0 and 10). It's not so much a matter of an efficient freezer as it is a matter of a well insulated ice box. I am able to maintain 20deg indefinitely running the thing for less than an hour a day since I beefed up the insulation when installing it.

I only run the thing once every 2-3 days now that it's cooler out and we're at the dock. It's my own choice that it gets up to close to 30F at times. Remember - I'm set up for life at anchor and a genset run each day, so the refrigeration system is set up like this too. It's a bit of a trade off for me.

Also, working aboard one megayacht, they had deep walk-in freezers below the aft deck. They were powered by quite a few compressors just like the one I describe above, lined up in the area just before you entered the engine room. The freezers had no trouble at all maintaining 0 degrees in the Caribbean... and these were walk-ins no less!

I think it has a lot more to do with insulation than compressors or efficient refrigeration systems when it comes to having an efficient freezer.
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Old 03-01-2007, 17:20   #13
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Very true, but it makes you wonder. Why don't the big manufacturers take out one or two of the "sleeps 10" berths in these new 35-40' boats, and install a big, well insulated freezer? Most of the time, I would much rather have a good steak, than over night guests
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Old 04-01-2007, 02:23   #14
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Quote:
Originally Posted by Kai Nui
Very true, but it makes you wonder. Why don't the big manufacturers take out one or two of the "sleeps 10" berths in these new 35-40' boats, and install a big, well insulated freezer? Most of the time, I would much rather have a good steak, than over night guests
In which case the ad’ might read:
“... sleeping for 8, cold storage* for 2 ...”
Perhaps not as appealing to most potential buyers as the former.

* morgue or mortuary
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Old 04-01-2007, 03:05   #15
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Most marine freezers are not kept cold enough, as a matter of practicality, for long-term frozen storage of food.

The food science/safety experts recommend freezer temperatures of 0 degrees F (-18 C). At this temperature, most bacterial growth is stopped (freezing does not kill most bacteria). At higher frozen temperatures (0 F to 30F) bacterial growth is slowed, but continues.
Though food will be safe indefinitely at 0 F, quality will decrease the longer the food is in the freezer.

Remember the three prongs of food safety: Hot, Cold and Clean.
In other words, keep hot foods hot, keep cold foods cold, and keep everything clean. Cold food should be refrigerated under 35 or 40 degrees Fahrenheit, and hot food maintained above 140 degrees.

When measuring the freezer temperature, place the thermometer between frozen food packages, for 5 to 8 hours.

To measure the temperature in the refrigerator, put the thermometer in a glass of water and place it in the middle of the refrigerator, for 5 to 8 hours.

ICE CREAM: Below about -25̊ C, ice cream is stable for indefinite periods without danger of ice crystal growth; however, above this temperature, ice crystal growth is possible and the rate of crystal growth is dependant upon the temperature of storage. This limits the shelf life of the ice cream.
The first rule of ice cream storage, is to avoid (as much as possible) temperature fluctuations during storage and distribution. Ice crystals need to be numerous and of small, uniform size so they are not detected when eaten. It is heat shock, large temperature fluctuations, which is the greatest culprit to the loss of these small, uniform ice crystal size distributions and resulting coarse, icy texture (recrystallization).
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