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Why Can You Only Reheat Food Once?  
User currently offlineRobK From United Kingdom, joined Sep 2004, 3945 posts, RR: 18
Posted (7 years 9 months 4 weeks 12 hours ago) and read 32203 times:

A question I've always wanted to know the answer to! You see on food packets instructions for reheating when you get it home, but then after that one-time reheat they say in big letters DO NOT REHEAT. Why is this?

Surely if you ensure the food is piping hot throughout then you can reheat it as many times as you want theoretically (although appreciate that that can only be done for so long before the food goes off).

 confused 

R

24 replies: All unread, jump to last
 
User currently offlineAloges From Germany, joined Jan 2006, 8617 posts, RR: 43
Reply 1, posted (7 years 9 months 4 weeks 12 hours ago) and read 32190 times:

It's because the bacteria on/in it (no, food is generally not sterile  Wink ) have a better chance to grow if you heat the food, let it cool off, heat it again and so on. Same goes for freezing thawed food.


Walk together, talk together all ye peoples of the earth. Then, and only then, shall ye have peace.
User currently offlineRobK From United Kingdom, joined Sep 2004, 3945 posts, RR: 18
Reply 2, posted (7 years 9 months 4 weeks 12 hours ago) and read 32175 times:

But surely -20C and 90C+ are temps too low and high for bacteria to survive?

R


User currently offlineAloges From Germany, joined Jan 2006, 8617 posts, RR: 43
Reply 3, posted (7 years 9 months 4 weeks 11 hours ago) and read 32155 times:

It's also about bacteria that get on the food while you handle it than about those that are already in it. There are some bacteria that do not get killed by -20°C or +90°C, such as the (in)famous Thermophilus aquaticus living in geysers. I'd really like to know what biochemicists would do without that little bugger.  Wink

Besides, re-heating food twice would probably make it disgustingly dry.



Walk together, talk together all ye peoples of the earth. Then, and only then, shall ye have peace.
User currently offlineKlaus From Germany, joined Jul 2001, 21353 posts, RR: 54
Reply 4, posted (7 years 9 months 4 weeks 10 hours ago) and read 32129 times:

As far as I remember, it is primarily because some of the substances contained in certain ingredients are chemically altered in the heating-cooling-reheating cycle and can become really unhealty after the second heating.

User currently offlineDeltaDC9 From United States of America, joined Apr 2006, 2844 posts, RR: 4
Reply 5, posted (7 years 9 months 4 weeks 9 hours ago) and read 32108 times:

Actually adding heat to food is in effect pre-digestion. Heat breaks down the molecules in a similar way as saliva and stomach acid, from complex to simple. That is why a raw food is much harder to digest than a cooked, there is more work to do.

Every tiime you add heat you are breaking it down further into something other than what it origiinally was.



Dont take life too seriously because you will never get out of it alive - Bugs Bunny
User currently offlineIFEMaster From , joined Dec 1969, posts, RR:
Reply 6, posted (7 years 9 months 4 weeks 9 hours ago) and read 32106 times:

My sister had a nasty case of lysteria (sp?) that was traced back to ice cream that melted and was refrozen.

Nasty.


User currently offlineWSOY From , joined Dec 1969, posts, RR:
Reply 7, posted (7 years 9 months 4 weeks 9 hours ago) and read 32093 times:

Quoting Klaus (Reply 4):
As far as I remember, it is primarily because some of the substances contained in certain ingredients are chemically altered in the heating-cooling-reheating cycle and can become really unhealty after the second heating.

A bit vague, wouldn't you say?

My understanding on the matter is simply that if the first heating has been even marginally inadequate for some reason, when the foodstuff is cooled down, any trace bacteria left will have had a good feast by the 2nd heating.

From http://www.foodsafety.gov/~fsg/f99broch.html

"Reheat carry-out meals and leftovers to a minimum internal temperature of 165° F and stir to cook evenly. Bring sauces, soups and gravy to a boil when reheating. "


User currently offlineKlaus From Germany, joined Jul 2001, 21353 posts, RR: 54
Reply 8, posted (7 years 9 months 4 weeks 9 hours ago) and read 32086 times:

Quoting WSOY (Reply 7):
A bit vague, wouldn't you say?

Absolutely - but I simply don't have more detailed information myself right now.

Quoting WSOY (Reply 7):
My understanding on the matter is simply that if the first heating has been even marginally inadequate for some reason, when the foodstuff is cooled down, any trace bacteria left will have had a good feast by the 2nd heating.

That is certainly true - but there are foods which should not be re-heated no matter how high the temperature was and is, such as spinach or mushrooms.


User currently offlineJ_Hallgren From United States of America, joined Jun 2000, 1507 posts, RR: 0
Reply 9, posted (7 years 9 months 4 weeks 9 hours ago) and read 32086 times:

I would also think it would greatly depend on the time interval between the reheat cycles...15-20 mins might be fine but 2-4 hrs may not be...etc...


COBOL - Not a dead language yet!
User currently offlineTWFirst From Vatican City, joined Apr 2000, 6346 posts, RR: 52
Reply 10, posted (7 years 9 months 4 weeks 9 hours ago) and read 32086 times:

WSOY: Are you from Decatur, IL by any chance?


An unexamined life isn't worth living.
User currently offlineDeltaDC9 From United States of America, joined Apr 2006, 2844 posts, RR: 4
Reply 11, posted (7 years 9 months 4 weeks 9 hours ago) and read 32079 times:

Quoting TWFirst (Reply 10):
WSOY: Are you from Decatur, IL by any chance?

If he was, would he admit it?



Dont take life too seriously because you will never get out of it alive - Bugs Bunny
User currently offlineWSOY From , joined Dec 1969, posts, RR:
Reply 12, posted (7 years 9 months 4 weeks 9 hours ago) and read 32067 times:

Quoting TWFirst (Reply 10):

I'm afraid my American experience is limited to a 1984 visit to upstate N.Y. and the province of Quebec. But I'm open to shortlisting Decatur, IL, over my targets in the U.S. if there's demand.

--

Can you remember who's saying spinach and mushrooms are dangerous to reheat, and why should they be?

[Edited 2006-06-28 22:56:50]

User currently offlineBobster2 From , joined Dec 1969, posts, RR:
Reply 13, posted (7 years 9 months 4 weeks 8 hours ago) and read 32058 times:

If you eat it, you'll die. If you don't eat, you'll die.

Use some common sense. If you're in good health and you've been eating food all your life, you can probably continue eating food, at least for a little while.

Seriously, the FDA says you must heat lunch meats before eating. Baloney! How many people reheat bologna before putting it in a sandwich?

Unless you're elderly or tend to get sick very easily, you can have a bologna sandwich and it won't kill you.

DISCLAIMER: Do not attempt to eat bologna without reheating except under the guidance of a food safety professional.


User currently offlineAloges From Germany, joined Jan 2006, 8617 posts, RR: 43
Reply 14, posted (7 years 9 months 4 weeks 8 hours ago) and read 32034 times:

Quoting DeltaDC9 (Reply 5):
Heat breaks down the molecules in a similar way as saliva and stomach acid, from complex to simple.

Sorry, but no.

I assume you're talking about the denaturation of proteins, the process you witness when cooking an egg? Denaturation does not equal proteolysis. Denaturation is the transformation of protein structure down to level two of four, if you excuse my informal choice of words, proteolysis is the destruction of the actual chain of amino acids which happens e.g. in your intestines.

Think of a protein as a long chain of amino acids that folds, spirals, twists and turns innumerable times before it can "go to work". Denaturation, usually irreversible, means these twists and turns are changed, but the chain itself is not broken. Your body uses a variety of enzymes for that task.

Finally, your stomach acid is mainly for disinfection - unless of course you define "stomach acid" as all the bodily fluids that are in the stomach. In that case, it would be the HCl in the stomach acid that is for disinfection.

And now for the Ode to Nexium...  duck 



Walk together, talk together all ye peoples of the earth. Then, and only then, shall ye have peace.
User currently offlineTWFirst From Vatican City, joined Apr 2000, 6346 posts, RR: 52
Reply 15, posted (7 years 9 months 4 weeks 7 hours ago) and read 32012 times:

Quoting WSOY (Reply 12):
'm afraid my American experience is limited to a 1984 visit to upstate N.Y. and the province of Quebec. But I'm open to shortlisting Decatur, IL, over my targets in the U.S. if there's demand.

The reason I ask is twofold... 1) Your username is the name of the largest radio station in Decatur (WSOY)... so named because the city was once the "Soybean Capital of the World", is still the Soy Capital of the US, and is home to the largest food processor in the world... Archer Daniels Midland Company. Thus, I thought perhaps you might be an employee.. perhaps even a food scientist... from ADM.



An unexamined life isn't worth living.
User currently offlineZRH From Switzerland, joined Nov 1999, 5564 posts, RR: 37
Reply 16, posted (7 years 9 months 4 weeks 7 hours ago) and read 31996 times:

Actually it very depends on what food, at what temperature, how long and at what temperature you kept it (frozen or not). Some you can't reheat at all some several times. As most people don't know they always write not to reheat.

User currently offlineRobK From United Kingdom, joined Sep 2004, 3945 posts, RR: 18
Reply 17, posted (7 years 9 months 4 weeks 5 hours ago) and read 31973 times:

Okay thanks for the replies! I could count on one hand the amount of times I've been ill in my entire life (very few) and certainly am not fussy when it comes to use-by dates etc. For example, even if milk is starting to smell a bit dodgy, if it's still completely in liquid form without any chunks in it then I'll still drink it!  bigthumbsup 

Never had any probs re-freezing or re-heating foods either, although the taste does begin to deteriorate somewhat. I just wondered what all the big fuss was about with them stating don't do this/don't do that etc, but seems to be nothing more than a bit of scare-mongering for those fussy eaters with weak bellies.  spin 

R


User currently offlineFokker Lover From , joined Dec 1969, posts, RR:
Reply 18, posted (7 years 9 months 4 weeks 5 hours ago) and read 31963 times:

Quoting IFEMaster (Reply 6):
My sister had a nasty case of lysteria (sp?) that was traced back to ice cream that melted and was refrozen.

She's very lucky that she wasn't pregnant at the time. It causes still born births.
I don't have my books right now, because I loaned them to friend. Otherwise I would be able to look up the bacterias and pathogens for you. I had to go to a 2 day food safe handling course when I opened my business.
41 F. to 130 F. is known as the danger zone. Bacteria thrives at those temps. Our hot hold temp is 135 F. Any kind of ground meat gets cooked to 165 F.
When I have more time I'll tell you about the dangers of potato salad and chicken salad. It's not the mayonaise. Mayo will get moldy, but it doesn't go bad. Mold is not considered dangerous.


User currently offlineHalls120 From , joined Dec 1969, posts, RR:
Reply 19, posted (7 years 9 months 4 weeks 4 hours ago) and read 31946 times:

Quoting Aloges (Reply 3):
Besides, re-heating food twice would probably make it disgustingly dry.

 checkmark 


User currently offlineWSOY From , joined Dec 1969, posts, RR:
Reply 20, posted (7 years 9 months 4 weeks 3 hours ago) and read 31927 times:

Quoting TWFirst (Reply 15):
WSOY

Some surprising coincidences in acronyms -- but nonetheless I've now set up my almost personal site: http://www.wsoy.fi/english


User currently offlineBraybuddy From Ireland, joined Aug 2004, 5576 posts, RR: 32
Reply 21, posted (7 years 9 months 3 weeks 6 days 20 hours ago) and read 31877 times:

Quoting RobK (Reply 17):
am not fussy when it comes to use-by dates etc. For example, even if milk is starting to smell a bit dodgy, if it's still completely in liquid form without any chunks in it then I'll still drink it!

Never had any probs re-freezing or re-heating foods either, although the taste does begin to deteriorate somewhat. I just wondered what all the big fuss was about with them stating don't do this/don't do that etc, but seems to be nothing more than a bit of scare-mongering for those fussy eaters with weak bellies.

Exactly. Sell-by dates are only manufacturers covering their arses. I'm amazed by the number of people who see something which has expired that day and treat it as if it were radioactive.

I've often used food stored in the fridge WEEKS after the sell-by date without any problem. My rule is, if it looks okay, it probably IS okay. (I've even been known to scrape a layer of mould off something and stick it in the microwave.)

And I've never had any problems reheating or refreezing food. Again I reckon it's the manufacturers covering their arses.

And as for milk . . . just as it is starting to turn it actually tastes GREAT! Not sour, but just slightly off.


User currently offlineWSOY From , joined Dec 1969, posts, RR:
Reply 22, posted (7 years 9 months 3 weeks 6 days 12 hours ago) and read 31840 times:

Quoting Braybuddy (Reply 21):
My rule is, if it looks okay, it probably IS okay.

You're in luck to be living under a Food Administration employing a different set of rules. The fact that for instance sour milk does not normally contain enough harmful bacteria to cause anything serious in a healthy individual is not an accident. The germs in foodstuff are never at rest, only temporarily weakened.


User currently offlineBobster2 From , joined Dec 1969, posts, RR:
Reply 23, posted (7 years 9 months 3 weeks 6 days 4 hours ago) and read 31801 times:

Time to get serious. The reason for the rule against reheating is that bacteria create toxins, and the toxins do not get eliminated by cooking.

But the rule is making pessimistic, worst case, assumptions; such as the assumptions that the food is kept at the wrong temperature for too long and stored for too long.

That's why I said to use common sense. The rule is overly strict for most situations. If you play it safe follow the rule. But if you have good experience with reheating leftovers then continue doing it.

The point is: they don't want people to think that cooking is some kind of magic that removes toxins and other bad thing in food. That's why they tell you not to reheat.


User currently offlineWSOY From , joined Dec 1969, posts, RR:
Reply 24, posted (7 years 9 months 3 weeks 5 days 15 hours ago) and read 31791 times:

Quoting Bobster2 (Reply 23):
and the toxins do not get eliminated by cooking.

"Not all", actually. http://www.cfsan.fda.gov/~dms/qa-fdb31.html


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