Jump to content

The magic sausage.


tomgwyther

Recommended Posts

Here's an odd phenomenon I can't quite figure out...

 

A microwaveable sausage comes wrapped in an air-tight bag (Similar to a bag of crisps/potato chips)

When I heat it in the microwave, the bag contracts around the food, as if a vacuum were being created.

The hot sausage comes out shrink-wrapped!

 

How is this possible, since the hot meat should make the available air in the bag expand like a balloon.

 

Microwaves only realy have a noticeable affect on sugar, water and fat molecules, not air, and in any case, the bag should expand as it heats.

 

How can hot air contract?

Is the meat absorbing the available air?

Could the humble sausage be breaking the laws of physics?

Will t.v dinners help us toward a unified theory of everything?

Why am I so concerned about my lunch in this way?

 

 

So many questions: Any answers?

 

 

p.s the same happens with hot lasagne in a bowl, wrapped in cling-film.

Link to comment
Share on other sites

A microwaveable sausage comes wrapped in an air-tight bag (Similar to a bag of crisps/potato chips)

When you heat some plastics, they can shrink. There is a kids toy call (here in Australia, I am not sure if they have the same name in other countries) call "Shrinkies".

 

What they are is a "tag" like piece of plastic a few centimetres across that kids can draw on and colour in. Once the kid has done this, it is placed in an oven for a certain period of time. While in the oven, then plastic shrinks down to around 1cm across.

 

If you sausage is wrapped in plastic (like chip packets), then the heat from the cooking sausage would cause this plastic to shrink.

 

The hot sausage comes out shrink-wrapped!

This is exactly what it is. Shrink wrapping use heat to cause the plastic wrapping to "Shrink". SO this is exactly what is happening to your sausage.

Link to comment
Share on other sites

Out here it's affectionately known as "varnish". What you do is get a tube of plastic, in a small diameter, then slightly heat it and stretch it to a larger tube. When heated, the plastic reverts to its original size.

 

It's used to secure wires. Instead of duct taping them (which leaves glue all over and they age and falls off with heat and water), such a tube is inserted over the wire and after soldering it's pulled over and heated. The plastic shrinks and looks just like the original isolation, protecting from hat, water, and non-aging.

Link to comment
Share on other sites

thanks for the input guys,

I repeated the 'experiment' but his time mesured to bag before and after cooking.

The mesurements came out the same i.e. the bag it's self did not shrink.

 

Other observations:

Condensation occurs inside the bag, telling us that the air is hotter inside than out

 

Most of the shrinking happens after cooking has stopped. Bear in mind the microwave energy has no major effect on the air in the bag, the heat from the food heats the air around it

 

The size of the bag never changes

 

The same shrink wrapping effect is observed when other heat sources are used (e.g. a hot lamp) the bag shrinks during heating.

 

The bag is not completely air tight, air can escape and appears to be being 'sucked' out.

 

The air pressure inside the microwave is constant (Microwaves are not air-tight).

 

 

Discuss

Link to comment
Share on other sites

My guess is that as the bag is heated it become more soft/flexible and collapses from both it's own weight and the weight of the condensation on the inside of it. Also condensation inside it would probably make it stick to the sausage better. Like a surface tension effect.

You ever try to stick a wet hand into a latex glove? It's impossible. The same thing happens when you wear to big gloves and your hands get sweaty, they stick like the air has been sucked out.

 

But your definition of shrink is confusing. Could you not take before and after pictures? That would help alot.

Link to comment
Share on other sites

I'm amazed no one has cracked a joke yet with the words sausage and shrink repeated sooooo many times.
Maybe it's just too obvious. ;)

 

I can only imagine it's the air humidity being absorbed by the wienies.

Link to comment
Share on other sites

you heated the sausage using microwaves, so it's safe to assume it has water content also becasue of the noted condensation on the inside.

as you heat it, the water begins to evaporate occupying volume, lets pretend the bag springs a leak (highly likely) so the air and water vapour begin to escape. when the cooking has finished, you'll have more water vapour than air inside the bag. (you can see where this is going) when the power is then turned off, there is nothing stopping the water condensing. liquid water takes up about 1/2000 times it's volume as steam.

Link to comment
Share on other sites

you heated the sausage using microwaves, so it's safe to assume it has water content also becasue of the noted condensation on the inside.

as you heat it, the water begins to evaporate occupying volume, lets pretend the bag springs a leak (highly likely) so the air and water vapour begin to escape. when the cooking has finished, you'll have more water vapour than air inside the bag. (you can see where this is going) when the power is then turned off, there is nothing stopping the water condensing. liquid water takes up about 1/2000 times it's volume as steam.

 

We have a winner!!!

 

I'm kinda embarrased I didn't come up with that. It's seems rather obvious now.

Link to comment
Share on other sites

Okay the last thing you have to do to check this is to observe the sausage while cooking.

 

If the shrinkage occurs prior to heathing stoping then you know this explaination is wrong.

If it occurs immediatley or shortly after stopping then it is correct.

Link to comment
Share on other sites

I'd lend you my vernier caliper if you were closer by. I expect the food to expand slightly from just heat expansion, and then there's vapor production, and also maybe puffing up from cooking (state change). Yes I feel silly, but I like a good Polish dog. Yes, Bluenoise, the possibilities here are pretty funny. I do keep lengths of shrink-tube from Radio Shack for electric wire splices. They shrink to about half-size under strong heat gun. . . . . . . . Hefting my trusty CRC tables, I see the vapor pressure of water doubles roughly every 12 degrees C.

Link to comment
Share on other sites

Some of you chemists can corroborate this but I think most molecular process doubles at about the same rate, so it is a cool thing to know. I deal professionally advising clients about the relative humidity in their homes vis-a-vis their pianos, and the facts of life with vapor pressure are not always intuitive. Now I can point them to this thread. The rates are expressed in kinetic theory. Ludwig Boltzmann shot himself in 1906, being deeply bummed out that no one would take seriously his atomic theory of kinetics. . . . . . . . . . . . . . . . I am trying to link his exponential to the quantum fields.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.