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RobK
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Why Can You Only Reheat Food Once?

Thu Jun 29, 2006 2:11 am

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 

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aloges
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RE: Why Can You Only Reheat Food Once?

Thu Jun 29, 2006 2:26 am

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.
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RobK
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RE: Why Can You Only Reheat Food Once?

Thu Jun 29, 2006 2:41 am

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

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aloges
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RE: Why Can You Only Reheat Food Once?

Thu Jun 29, 2006 2:57 am

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.
Don't cry because it's over, smile because it happened.
 
Klaus
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RE: Why Can You Only Reheat Food Once?

Thu Jun 29, 2006 4:13 am

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.
 
deltadc9
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RE: Why Can You Only Reheat Food Once?

Thu Jun 29, 2006 4:49 am

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.
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IFEMaster
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RE: Why Can You Only Reheat Food Once?

Thu Jun 29, 2006 4:52 am

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

Nasty.
Delivering Anecdotes of Dubious Relevance Since 1978
 
WSOY
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RE: Why Can You Only Reheat Food Once?

Thu Jun 29, 2006 5:18 am

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. "
"Nukkuessa tulee nälkä" (Nipsu)
 
Klaus
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RE: Why Can You Only Reheat Food Once?

Thu Jun 29, 2006 5:22 am

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.
 
j_hallgren
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RE: Why Can You Only Reheat Food Once?

Thu Jun 29, 2006 5:23 am

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...
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TWFirst
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RE: Why Can You Only Reheat Food Once?

Thu Jun 29, 2006 5:23 am

WSOY: Are you from Decatur, IL by any chance?
An unexamined life isn't worth living.
 
deltadc9
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RE: Why Can You Only Reheat Food Once?

Thu Jun 29, 2006 5:32 am

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
 
WSOY
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RE: Why Can You Only Reheat Food Once?

Thu Jun 29, 2006 5:46 am

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]
"Nukkuessa tulee nälkä" (Nipsu)
 
Bobster2
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RE: Why Can You Only Reheat Food Once?

Thu Jun 29, 2006 5:56 am

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.
"I tell you this, no eternal reward will forgive us now for wasting the dawn." Jim Morrison
 
aloges
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RE: Why Can You Only Reheat Food Once?

Thu Jun 29, 2006 6:32 am

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 
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TWFirst
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RE: Why Can You Only Reheat Food Once?

Thu Jun 29, 2006 6:54 am

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.
 
ZRH
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RE: Why Can You Only Reheat Food Once?

Thu Jun 29, 2006 7:06 am

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.
 
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RobK
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RE: Why Can You Only Reheat Food Once?

Thu Jun 29, 2006 8:52 am

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 

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RE: Why Can You Only Reheat Food Once?

Thu Jun 29, 2006 9:29 am

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.
10,000 years ago we would have eaten you. Today, we drag you along and allow you to pollute the gene pool.
 
halls120
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RE: Why Can You Only Reheat Food Once?

Thu Jun 29, 2006 10:46 am

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

 checkmark 
"Suppose you were an idiot. And suppose you were a member of Congress. But I repeat myself." Mark Twain, a Biography
 
WSOY
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RE: Why Can You Only Reheat Food Once?

Thu Jun 29, 2006 11:23 am

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
"Nukkuessa tulee nälkä" (Nipsu)
 
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Braybuddy
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RE: Why Can You Only Reheat Food Once?

Thu Jun 29, 2006 6:09 pm

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.
 
WSOY
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RE: Why Can You Only Reheat Food Once?

Fri Jun 30, 2006 2:41 am

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.
"Nukkuessa tulee nälkä" (Nipsu)
 
Bobster2
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RE: Why Can You Only Reheat Food Once?

Fri Jun 30, 2006 10:26 am

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.
"I tell you this, no eternal reward will forgive us now for wasting the dawn." Jim Morrison
 
WSOY
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RE: Why Can You Only Reheat Food Once?

Fri Jun 30, 2006 11:13 pm

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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