Freezer Temperature

[Ian]

We are advised to set our freezer temperature to -18C (0F)

Why?

I would like to save some electricity and warming up the freezer would help a lot. I heard a programme on Radio 4 some months ago about the history of Birds Eye, during the programme one of the directors said they were researching storing food at a higher temperature because it did not seem to have any advantage to freeze so cold and was probably unnecessary. Having contacted Birds Eye in the UK they have no knowledge of this research.

I have been hunting for some weeks now to find out why -18C is recommended. Two reasons have surfaced but I am not convinced.
1. 0F is easy to remember and set things to.
2. -18C is low enough that when unfrozen food is put in to freeze the thermal mass is enough that the frozen food will not thaw before the compressor can cool the new food enough.

But it would be simple to set the day to day running to, say, -10C but pre-cool to -18C when freezing large amounts of food.

Does anybody know of a good reason to run at -18C as against, say, -10C or even -5C, apart from "it is recommended". If -18C is good why is it not -25C?

My back of the envelope calculations show a 20% saving in electricity running at -10C which is not inconsiderable.

[diamond lil]

I think it would be quite ok to stay at -5C, it seems a very arbritary setting of -18.As long as you hit the fast freeze button when adding new stuff.

[counsellor]

I believe that freezing only slows the rate of decay and doesn’t stop it,
however the colder an item is the slower the rate of decay
So I think it is one of those sums of cost against effect

[Ian]

The Birds Eye site says:

"There is no time limit to how long food can be safely frozen for - as long as it is kept frozen at -18 degrees Celsius or below and remains properly frozen, it will not become unsafe."

So -18C is good but no justification is given just the statement. But why -18C? it is a puzzle.

[Carrot Cruncher]

Just had a look on a US government health site and it says the same regarding the -18c figure.

It's reasoning is that -18c (zero F) is the point where bacteria become inactive, any temp above that (even if still below zero centigrade) means that the bacteria is still active but slowed down.

According to the site any time limits on food stored at -18c or below is due to taste and/or texture not for health reasons