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Author Topic: Can flasks keep food hot?  (Read 8898 times)

Offline 22A

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Can flasks keep food hot?
« on: 20/09/2011 20:19:29 »
I have a very effective metal flask which if you put in boiling water for an hour, throw that away and then put in your drink, it keeps the drink hot for 14 hours.
If having thrown the initial hot water away, instead of putting in a drink, I put in freshly oooked sausages instead, would they remain hot?
I think they would as, being a vacuum, there's nowhere for the heat to go.
My wife argues that the sausages would lose enough heat to make them dangerous to eat.
« Last Edit: 22/09/2011 21:50:27 by chris »


 

Offline techmind

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Re: Can flasks keep food hot?
« Reply #1 on: 20/09/2011 21:17:24 »
If you just put a couple of loose sausages in the flask I think you'd find they cool down quite quickly.
The issue is that even if you put them in at a similar temperature to a hot drink, the fact that the sausages are much smaller than the total volume of the flask, and have a lower heat capacity, they'll cool down quickly.
You'd probably find the same thing if you only put half a mug of hot water/beverage in your flask.

If you managed to pack the sausages in gravy (or baked beans?) so the flask is essentially full then you might make it work.

Another approach might be if you could surround the sausages with a close-fitting plastic pouch containing boiling water/tea/coffee/sauce etc - all inside the flask. Again in this way you've maximised the heat-capacity of hot-stuff inside.


*** This reply only considers the physics. I can say little about the biological/spoilage issues.
 

Offline Geezer

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Re: Can flasks keep food hot?
« Reply #2 on: 20/09/2011 23:08:37 »
It depends on how hot you want to keep your sausages  ;D

Assuming your flask is highly effective, the only place the heat from the sausages can go is into whatever else is inside the flask. Absent anything else, that would probably be air. The more sausages you can cram into your flask, the less air there will be to heat up, and the hotter your sausages will remain.

You could put in the sausages then immediately fill the rest of the flask with boiling water. That ought to keep the sausages pretty close to 100°C for quite a while. You could even use hot oil instead of water, but that could be a bit dangerous.
 

Offline peppercorn

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Re: Can flasks keep food hot?
« Reply #3 on: 22/09/2011 11:15:53 »
...fill the rest of the flask with boiling water
No one wants a soggy sausage [xx(]

You could even use hot oil instead of water, but that could be a bit dangerous.
And there's nothing worse than over oiling ya sausage!


.... Uhum!

If you can get the air surrounding the sausages fairly hot (say 60C, with a hairdrier say) the overall temp should equalise at nearer 90C - I assume the meat is cooked thoroughly to over 150C throughout.

A good guide would be to find out how hot those cabinets in the local chippy are kept.
« Last Edit: 22/09/2011 11:20:12 by peppercorn »
 

Offline Geezer

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Re: Can flasks keep food hot?
« Reply #4 on: 22/09/2011 17:06:22 »
You could also fill up the space with polystyrene packing worms :D, although hot mashed potatoes might be a better idea.
 

Offline imatfaal

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Re: Can flasks keep food hot?
« Reply #5 on: 22/09/2011 18:30:34 »
bangers and mash in a flask - brilliant, i love it!  you should patent that idea - oh god what have i said
 

Offline damocles

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Re: Can flasks keep food hot?
« Reply #6 on: 22/09/2011 19:00:45 »
No vacuum flask is perfect. The crucial thing in this scenario is the amount of heat that is lost via whatever leakage mechanisms are available, and the consequent temperature change.

The amount of heat that is lost by leakage, to a good approximation, depends only on the temperature difference between the contents and the outside world.

The temperature change that results from this heat loss depends on the thermal inertia, that is, the total heat capacity of the flask contents. If the flask were totally full of water, this would give just about the maximum possible thermal inertia, and the minimum temperature drop. Water has a higher specific heat than nearly anything else.

Packing the sausages in water is therefore the best solution if this were the only consideration. But it is not:

Quote
No one wants a soggy sausage

There are several suggestions in the thread about how to pack the sausages in material with high heat content. The most practical seem to be the ones about packing in mash or beans or gravy.

If you wanted your sausages uncontaminated by immersion, then one possibility with a really high thermal inertia would be to pack them in wheat grains. Somehow it sounds safer and more palatable than using polystyrene worms for packing. Not sure the latter would not melt nor stick to the sausages, etc.

 

Offline Geezer

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Re: Can flasks keep food hot?
« Reply #7 on: 22/09/2011 20:09:54 »

bangers and mash in a flask - brilliant, i love it!  you should patent that idea - oh god what have i said


I claim:

1. A heat transfer prevention device, including pre-heated processed animal protein, animal fat, and vegetable starch.

2. The heat transfer prevention device of claim 1 wherein the heat is prevented from transferring by a layer of nothing.

3. The heat transfer prevention device of claim 1 wherein the processed animal protein is a plurality of bangers.

4. The heat transfer prevention device of claim 1 wherein the vegetable starch is mash.
« Last Edit: 22/09/2011 20:21:22 by Geezer »
 

Offline Bored chemist

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Can flasks keep food hot?
« Reply #8 on: 23/09/2011 07:12:52 »
...fill the rest of the flask with boiling water
No one wants a soggy sausage [xx(]

You could even use hot oil instead of water, but that could be a bit dangerous.
And there's nothing worse than over oiling ya sausage!


.... Uhum!

If you can get the air surrounding the sausages fairly hot (say 60C, with a hairdrier say) the overall temp should equalise at nearer 90C - I assume the meat is cooked thoroughly to over 150C throughout.
The assumption that something which is mainly water gets heated to 150C seems odd.
Rinsing the flask with boiling water as in the OP will heat the flask and the air in it.
The biggest problem is that there's just not so much stuff in the flask, so there's less stuff to retain heat.
 

Offline peppercorn

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Can flasks keep food hot?
« Reply #9 on: 23/09/2011 15:50:09 »
The assumption that something which is mainly water gets heated to 150C seems odd.
Rinsing the flask with boiling water as in the OP will heat the flask and the air in it.
The biggest problem is that there's just not so much stuff in the flask, so there's less stuff to retain heat.

My assumption was that a good quality banger would be mainly fats.

If you wanted your sausages uncontaminated by immersion, then one possibility with a really high thermal inertia would be to pack them in wheat grains.

How about corn instead of wheat - then you've got dessert as well -> Pop-corn! :D
 

Offline Geezer

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Can flasks keep food hot?
« Reply #10 on: 24/09/2011 07:05:36 »
The assumption that something which is mainly water gets heated to 150C seems odd.
Rinsing the flask with boiling water as in the OP will heat the flask and the air in it.
The biggest problem is that there's just not so much stuff in the flask, so there's less stuff to retain heat.

My assumption was that a good quality banger would be mainly fats.

If you wanted your sausages uncontaminated by immersion, then one possibility with a really high thermal inertia would be to pack them in wheat grains.

How about corn instead of wheat - then you've got dessert as well -> Pop-corn! :D

The obvious solution is to cram the flask full of cooked sausage meat without the casings, then inject the meat into casings at the time of consumption with a bicycle pump.

(I'm pretty sure this would also work with spam.)
« Last Edit: 24/09/2011 19:47:41 by Geezer »
 

Offline Mazurka

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Can flasks keep food hot?
« Reply #11 on: 26/09/2011 13:04:00 »
No, the obvious solution is hotdog sausages...

 

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Can flasks keep food hot?
« Reply #11 on: 26/09/2011 13:04:00 »

 

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