Naked Science Forum
General Science => General Science => Topic started by: techmind on 07/07/2009 21:36:59
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Food-books / programmes and food-packaging frequently warns against re-freezing previously-frozen food. Examples include New Zealand lamb, and some fish, which are sold refridgerated but have been previously frozen. The packaging on some foods which are sold frozen (including some ready meals) warn against allowing the product to thaw then re-freezing.
Why is this such a big no-no?
What if I bought something refridgerated intending to use it the following day, but put it too near the top/back of my fridge and it froze overnight. Surely the product won't be more harmful the next day than if it had merely been refridgerated at 5C overnight?
I'm guessing the rule is a simplification, but am interested to know what's behind it - as I suspect the warnings have also attracted some additional urban myths.
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I was about to type out a reply.. but The Straight Dope sums it up nicely...
http://www.straightdope.com/columns/read/2232/why-is-refreezing-food-bad-what-exactly-is-freezer-burn
"Refreezing is bad for three reasons. First, by refreezing food you multiply the damage to it--any cells that escaped rupture the first time the food was frozen are at risk of being ruptured the second time. Second, when food has been frozen and thawed out, it has larger pockets of liquid within it than the first time due to the ruptured cells. When the food is refrozen, the larger pockets of liquid can freeze into much larger ice crystals, which can tear through many more cell membranes and lead to more damage to the food. (The best way to avoid cell damage, incidentally, is flash-freezing, which produces smaller ice crystals, minimal cell damage, and maximum freshness.)
The third and most important reason not to refreeze is increased risk of spoilage due to microorganisms. Many people thaw food by letting it sit at room temperature for several hours, giving the microorganisms in it time to get busy and partially spoil the food before it's refrozen. The problem is particularly pronounced in large pieces of meat such as a turkey, some parts of which may be at or near room temperature for hours during thawing. That's why turkeys should be thawed in a sink filled with water--the water equalizes the temperature and makes for faster thawing. Alternatively, you can thaw in the refrigerator, which is slower but retards spoilage by keeping the meat cool. Even so you're likely to have some multiplication of microorganisms. If you refreeze and rethaw, you've subjected the food to double the microorganism growth and double the fun. "
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interesting JnA.. I always wondered that as techmind...Thanks..
I defrost my Turkeys in the sink full of water also!
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What does it matter if cells are ruptured? I intend to rupture the cells when I start chewing them anyway
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What does it matter if cells are ruptured? I intend to rupture the cells when I start chewing them anyway
tougher meat and poorer taste
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I see. Why does it get tougher?
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What does it matter if cells are ruptured? I intend to rupture the cells when I start chewing them anyway
tougher meat and poorer taste
Now that's very well done. [8)]
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I see. Why does it get tougher?
Less water I suppose. But that is just stating the obvious.
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I see. Why does it get tougher?
Less water I suppose. But that is just stating the obvious.
loss of proteins as well
"In addition, reactions between the fluids liberated from the cells and the fluids that were in the intercellular spaces to start with almost always result in a poorer taste."
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this was a great read I have been told this and avoid refeezing but did not know the reason for it,learn something new everyday will not refreeze again...cheers
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Ice cream: the commercial stuff is aerated with very small bubbles, so when they have evaporated you have a mixture of water soluble oils, water and emulsifiers and flavours natural or artificial.
If you look back at how ice cream was made before electricity over salt water freezing mixtures and air whipped in, then letting it thaw and refreezing isn`t a very pertinent example I`m afraid.