However, what I did ask is how much the temperature in the cavity of a 'frost free' freezer rises during the 'no active cooling' part of the defosting cycle - do you know the answer to that?
I would think this varies, clearly above freezing and for long enough to drain, this is why frost free freezers need an ambulant temperature of around 12°C if too low it will not drain fully, seem to remember the reefer container size freezer was around 20 minutes, but likely domestic down to couple on minutes, unlikely to be a set time for all would depend on design. It was a long time ago 1980 that I worked in Algeria on freezers.
Even if that were true, "a couple of minutes" (or even very many minutes) 'above freezing' would not have any appreciable impact on the temperature of the contents, woiuld it?
However, I'm pretty confused. Once the 'active cooling' is switched off, I don't see any real difference between an upright ('frost free') and chest freezer (provided doors/lids remained closed). In either case, maintenance of the low cavity temp is totally dependent upon the insulation (and ambient temp) - which, again in either case, should mean that it would take many hours (maybe even a day or two) for the temp of the cavity (largely full of 'massive' contents, initially at -18°C) to rise from normal operating temp to 'above freezing', wouldn't it? What am I missing?
Re-freezing in a domestic freezer is a slow process at -18°C, blast freezing in the food processing factory is a very fast process at much lower temperatures -40°C. Slow freezing can significantly damage the texture and appearance of the food, blast freezing does less damage to the product.
It maybe that manufacturers advise against re-freezing due not health safety but the less attractive appearance of slow frozen products.
That said food that has been at room temperature after thawing is very likely to have bacterial colonies that began developing after thawing. These will be viable and increasing until the product is cooked and the majority of them are destroyed. They will not be destroyed if the product is re-frozen and the larger number of colonies means there is more chance of some surviving when the product is finally cooked.
That would be more consistent with my view. However, it's not just the manufacturers - for example, the FSA advise (presumably for 'food safety' reasons) that thawed food should not be re-frozen unless it is 'cooked' before the re-freezing.
That said food that has been at room temperature after thawing is very likely to have bacterial colonies that began developing after thawing. These will be viable and increasing until the product is cooked and the majority of them are destroyed. They will not be destroyed if the product is re-frozen and the larger number of colonies means there is more chance of some surviving when the product is finally cooked.
That's all conceptually true. However, returning to room temp and remaining at room temp for a significant time is not really often going to be the situation in the context of the 'freezer failures' we are discussing. Very very few bacteria will start replicating significantly until the temp rises to +5°C or above. Despite what I go on to say below, I would personally not re-freeze something that had been at room temp for a significant period of time - and I certainly would not re-freeze anything that was destined tio be eaten without subsequent 'proper cooking'.
However, what 'trumps' most of that is the fact that very very few pathogenic bacteria (or their toxins) will survive 'proper cooking' immediately prior to their ultimate consumption, even if they are present in fairly 'large quantities' due to happenings during previous storage. As I've said, I would be much more cautious about anything destined to be eaten without any further cooking.
Once the 'active cooling' is switched off, I don't see any real difference between an upright ('frost free') and chest freezer (provided doors/lids remained closed).
If switched off at end of freeze cycle only difference is upright relies on door seals and chest does not, upright not as efficient as chest. It only makes a difference if during defrost cycle, around a 140 watt heater on for 5 minutes is enough to defrost top of freezer if motor does not switch back on after the cycle. Heat raises so food at bottom will remain frozen, only food at top will defrost, if motors start then air is circulated so all parts same temperature.
It only makes a difference if during defrost cycle, around a 140 watt heater on for 5 minutes is enough to defrost top of freezer if motor does not switch back on after the cycle.
If (despite the 'frost free') frost/ice develops within the cavity, isn't that most likely to occur at the coldest part of the cavity (i.e. the bottom)? If so, then (with the fan off) raising the temp at just the top of the cavity is not going to help very much, is it?
In any event, I still doubt that raising the temp of (the air at the top of) the cavity will have much impact on the temperature of the ('frozen') contents.
However, I think I'm coming to understand the wisdom of my having largely stuck to chest freezers (and manual defrosting thereof)
Thanks. If I understand that correctly, the heater is heating back of the 'panel', rather than the cavity of the freezer. That's presumably fine for melting and frost/ice on the inner side of the panel, but I would have thought would have minimal effect on the temperature within the cavity, let aklone the contents of the freezer?
I would be very interested to know what a temperature probe would show of changes (if any measurable) of the within-cavity (or 'within-contents') temp during the defrosting phase of the cycle.
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Where is this 'heater'? Is it really in the freezer cavity?
