tomgwyther Posted January 24, 2007 Posted January 24, 2007 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.
Edtharan Posted January 24, 2007 Posted January 24, 2007 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.
Ndi Posted January 24, 2007 Posted January 24, 2007 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.
tomgwyther Posted January 24, 2007 Author Posted January 24, 2007 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
swansont Posted January 24, 2007 Posted January 24, 2007 If the bag didn't shrink, then the sausage expanded.
Bluenoise Posted January 24, 2007 Posted January 24, 2007 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.
Asy☼um 8 Posted January 24, 2007 Posted January 24, 2007 Oh my god, I'm so insanely glad this place isn't so uptight like every other site! I love this site guys! =]
Bluenoise Posted January 25, 2007 Posted January 25, 2007 Oh my god, I'm so insanely glad this place isn't so uptight like every other site! I love this site guys! =] I'm amazed no one has cracked a joke yet with the words sausage and shrink repeated sooooo many times.
tomgwyther Posted January 31, 2007 Author Posted January 31, 2007 Behold!! photographic evidence of the elusive sausages ... The dimentions of the bag and food therein remain the same, although the bag does expand like a ballon whilst in the microwave, only when cooking is finished does the air in the bag disappear. photo at http://www.redweaselmusic.co.uk/sausages
reor Posted January 31, 2007 Posted January 31, 2007 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.
Meir Achuz Posted February 1, 2007 Posted February 1, 2007 Please don't quote me, but maybe the frozen sausage was frozen. When it thawed, it could become softer and the pressure of the bag could squeeze it. This is hardly rocket science.
little guy Posted February 4, 2007 Posted February 4, 2007 then what would have happened to all of the air in the bag? it just "magically" condenses. I am sorry if this is a stupid question, because I am probably just missing something
Rocket Man Posted February 4, 2007 Posted February 4, 2007 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.
Bluenoise Posted February 4, 2007 Posted February 4, 2007 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.
tomgwyther Posted February 5, 2007 Author Posted February 5, 2007 Thanks Rocket man. You've answered my original question perfectly, I does seem very obvious now, water vapour condecsing in Volume, D'oh ! Now I can wat my dinner AND sleep at night
YT2095 Posted February 5, 2007 Posted February 5, 2007 I am sorry if this is a stupid question, because I am probably just missing something this coming from someone called "Little Guy" in a thread about Sausages and shrinking:-p:D ya just gotta love it!
Bluenoise Posted February 5, 2007 Posted February 5, 2007 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.
YT2095 Posted February 5, 2007 Posted February 5, 2007 actualy, I`d cut one open Before cooking, take the plastic off and test a sample in boiling water from the kettle, see what it does then.
Norman Albers Posted February 5, 2007 Posted February 5, 2007 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.
Norman Albers Posted February 6, 2007 Posted February 6, 2007 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.
Tom Mattson Posted February 6, 2007 Posted February 6, 2007 Could the humble sausage be breaking the laws of physics?
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