# Gasoline Sheen on Roast Beef? **URL:** \ **Category:** Factual Questions\ **Created:** [December 19, 2002, 1:20pm UTC](https://boards.straightdope.com/t/gasoline-sheen-on-roast-beef/143784 "2002-12-19T13:20:13Z")\ **Posts on this page:** 19\ **Page:** 1
**Author:** ![Phlosphr](https://avatars.discourse-cdn.com/v4/letter/p/c68b51/32.png) [@Phlosphr](https://boards.straightdope.com/u/Phlosphr)\ **Post date:** [December 19, 2002, 1:20pm UTC](https://boards.straightdope.com/t/gasoline-sheen-on-roast-beef/143784/1 "2002-12-19T13:20:13Z")
Ok can anyone out there in the teeming zillions tell me what that sheen is on store bought Roast Beef, Turkey, Ham ? Obviously it’s not dipped in gasoline, but there is definitely a rainbow colored sheen on the meat. Barring this is a flashback from my more lucid days there must be a logical reason what the meat is colored… ---
**Author:** ![RealityChuck](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/realitychuck/32/195_2.png) [@RealityChuck](https://boards.straightdope.com/u/RealityChuck)\ **Post date:** [December 19, 2002, 1:25pm UTC](https://boards.straightdope.com/t/gasoline-sheen-on-roast-beef/143784/2 "2002-12-19T13:25:51Z")
“Don’t eat green meat, it ain’t good for you. Killed your father, killed your sister, too.” ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [December 19, 2002, 1:34pm UTC](https://boards.straightdope.com/t/gasoline-sheen-on-roast-beef/143784/3 "2002-12-19T13:34:53Z")
That rainbow pattern can be caused by a thin layer of any transparent substance. It’s an interference pattern - the light reflected from the front surface interferes with light from the far side. At certain wavelength they will interfere constructively, and at others they will interfere destructively (i.e. cancel each other out). A thin layer of gasoline on top of water (or wet concrete) is a common example. You can also see it on soap bubbles. A perfectly uniform layer will simply make a reflection with a uniform color. Look into a camera lens or a coated eyeglass lens and you’ll see purple or deep green reflections created by the lens coating. (If all reflections are white, you’ve got a cheap uncoated lens.) I’m not so sure about meat, but it must be a thin layer of animal fat which ended up on the cut surface. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [December 19, 2002, 2:25pm UTC](https://boards.straightdope.com/t/gasoline-sheen-on-roast-beef/143784/4 "2002-12-19T14:25:05Z")
I’ve seen this before on uncooked bacon; rather than being caused by a thin layer on the surface, it seems to be some light effect caused by looking at the muscle fibres end-on. Probably is some sort of interference effect though. ---
**Author:** ![Popup](https://avatars.discourse-cdn.com/v4/letter/p/94ad74/32.png) [@Popup](https://boards.straightdope.com/u/Popup)\ **Post date:** [December 19, 2002, 2:33pm UTC](https://boards.straightdope.com/t/gasoline-sheen-on-roast-beef/143784/5 "2002-12-19T14:33:24Z")
Yup, I believe that **Mangetout** is on the right track. **Alton Brown** claims that it’s birefringence, and I’m bound to agree: > [@](#): > > Speaking of color, you ever notice the rainbow effect that sometimes appears on the surface of freshly cut tuna? It’s not from age and it’s not fat. It’s birefringence. > [reading from a book] "\*Anisotropism of the refractive index which varies as a function of polarization and fre … " (from [here](http://www.goodeatsfanpage.com/Season6/TunaTranscript.htm)) ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [December 19, 2002, 2:44pm UTC](https://boards.straightdope.com/t/gasoline-sheen-on-roast-beef/143784/6 "2002-12-19T14:44:36Z")
Is it just me or would **Birefringence** make a good user name? ---
**Author:** ![lieu](https://avatars.discourse-cdn.com/v4/letter/l/c2a13f/32.png) [@lieu](https://boards.straightdope.com/u/lieu)\ **Post date:** [December 19, 2002, 2:47pm UTC](https://boards.straightdope.com/t/gasoline-sheen-on-roast-beef/143784/7 "2002-12-19T14:47:55Z")
It’s common with roadkill. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [December 19, 2002, 3:02pm UTC](https://boards.straightdope.com/t/gasoline-sheen-on-roast-beef/143784/8 "2002-12-19T15:02:04Z")
So I was wrong - it’s not interference between two sides of a film, but interference caused by a pattern of muscle fibers. Neat. That’s how butterfly wings are colored, by the way. The pattern on CDs and laser disks also create color this way. It’s not _birefringence_ though, it’s just interference. Birefringence refers to multiple refraction, and happens in crystals whose index of refraction depends on polarization of light. Calcite crystal is a classic example - if you look through it you see two refracted images. ---
**Author:** ![Popup](https://avatars.discourse-cdn.com/v4/letter/p/94ad74/32.png) [@Popup](https://boards.straightdope.com/u/Popup)\ **Post date:** [December 19, 2002, 4:12pm UTC](https://boards.straightdope.com/t/gasoline-sheen-on-roast-beef/143784/9 "2002-12-19T16:12:50Z")
Actually, **scr4** , Untill last week I thought so to, but I have recently read about this in several places, and it would indeed seem like _collagen_ is birefringent. For example look at [this](http://www.aps.uoguelph.ca/~swatland/ch2_3.htm) > [@](#): > > Unstained collagen fibers may be seen by polarized light since they are birefringent (light that comes through Polaroid sunglasses is polarized, with all its waves in one plane; birefringent means having two refractive indices). By rotating the plane of polarized light, collagen fibers appear bright against an otherwise dark background (when two Polaroid lenses are perpendicular they block most of the light, but collagen fibers can rotate the light so that they appear bright). The birefringence of collagen fibers in meat is lost at the point during heating when gelatinization occurs. Collagen fibers have a wavy or crimped appearance which disappears when they are placed under tension. It appears that it’s mainly the connective tissue that’s birefringent, so maybe you can say that a ‘rainbowy’ pattern on your meat cut means that it’s not the most tender. Have a look at that page, as it lists quite a few interesting properties of meat. Just quoting wildly: > [@](#): > > the amount of connective tissue on a cut meat surface may be measured very rapidly. Peak excitation is around 370 nm so that the prominent 365 nm peak emission of a mercury arc lamp may be used. Some indication of collagen fiber diameter may be obtained by spectrofluorometry (measuring the wavelengths of fluorescence) because the fluorescence is quenched (fades) fairly rapidly. Thus, large collagen fibers retain a central core with a pre-quenching emission spectrum for longer than small fibers. > … That guy has seriously investigated the chemical, physical and optical properties of meat, and how they relate to everyday sensations souch as ‘toughness’ and ‘tenderness’. He’s the **Cecil Adams** of the meat trade! ---
**Author:** ![Popup](https://avatars.discourse-cdn.com/v4/letter/p/94ad74/32.png) [@Popup](https://boards.straightdope.com/u/Popup)\ **Post date:** [December 19, 2002, 4:18pm UTC](https://boards.straightdope.com/t/gasoline-sheen-on-roast-beef/143784/10 "2002-12-19T16:18:02Z")
Sorry. Just as I submitted that I realized that my argument doesn’t quite hold water. Birefringence would indeed give a ‘rainbowy’ pattern, but only if viewed through a polarising filter. I would rather agree with **scr4** that the rainbow pattern is caused by interference from closelly packed muscle fibers. The fact that there is _also_ birefringence is something else… And something you wouldn’t see unless you were wearing your sunglasses. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [December 19, 2002, 4:33pm UTC](https://boards.straightdope.com/t/gasoline-sheen-on-roast-beef/143784/11 "2002-12-19T16:33:52Z")
Just another log on the interference pattern fire: [Surface roughening during slicing of precooked cured beef round muscles reduces iridesence](http://www.foodscipress.com/JMFV13.1.htm#Surface%20Roughening%20Of%20Precooked) ---
**Author:** ![fiddlesticks](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fiddlesticks/32/18129_2.png) [@fiddlesticks](https://boards.straightdope.com/u/fiddlesticks)\ **Post date:** [December 19, 2002, 5:28pm UTC](https://boards.straightdope.com/t/gasoline-sheen-on-roast-beef/143784/12 "2002-12-19T17:28:54Z")
\ Mmmmmmmm…gasoline sheen… \ 😃 ---
**Author:** ![susan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/susan/32/17537_2.png) [@susan](https://boards.straightdope.com/u/susan)\ **Post date:** [December 19, 2002, 5:36pm UTC](https://boards.straightdope.com/t/gasoline-sheen-on-roast-beef/143784/13 "2002-12-19T17:36:38Z")
Birefringence seems like a good cat name, if not a good user name. ---
**Author:** ![SandWriter](https://avatars.discourse-cdn.com/v4/letter/s/8491ac/32.png) [@SandWriter](https://boards.straightdope.com/u/SandWriter)\ **Post date:** [December 19, 2002, 7:17pm UTC](https://boards.straightdope.com/t/gasoline-sheen-on-roast-beef/143784/14 "2002-12-19T19:17:19Z")
Hey Phlosphr, I noticed that sheen as well. Till today I used to think it was either a little bit of soap, or the start of the meat going rotten. I usually ate it anyway as it wasn’t past the expiration date. When I didn’t get sick I just continued to ignore it. Now, thanks to you and the straight dope, I know it’s just a property of poor quality meat. On the topic, what can you tell about meat by shining light on it, I’m sure it has to do with computer controlled meat grading or something like that. Can you imagine tons of meat rolling down a conveyer belt, a strobe light flashes so fast it looks like a steady shine. Each flash takes a picture of a chunk of meat and a grape juice filled ink jet printer head writes some info on the just flashed meat. I guess the whole deal would have to be in a refrigerated building. ummmm, meat and technology, it’s a beautiful thing. ---
**Author:** ![Duckster](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/duckster/32/1244_2.png) [@Duckster](https://boards.straightdope.com/u/Duckster)\ **Post date:** [December 19, 2002, 9:21pm UTC](https://boards.straightdope.com/t/gasoline-sheen-on-roast-beef/143784/15 "2002-12-19T21:21:24Z")
> [@](#): > > \*Originally posted by lieu \* > \*\*It’s common with roadkill. \*\* The voice of experience, eh? 😃 ---
**Author:** ![squid](https://avatars.discourse-cdn.com/v4/letter/s/bbce88/32.png) [@squid](https://boards.straightdope.com/u/squid)\ **Post date:** [December 19, 2002, 10:30pm UTC](https://boards.straightdope.com/t/gasoline-sheen-on-roast-beef/143784/16 "2002-12-19T22:30:20Z")
When I was a deli manager I once asked the same question to my sales rep. His responce was simply “is normal, don’t worry about it”. That seemed to make me worry even more. Probably some “meat addictive chemical” applied by the Cattle Nazies. Pass the bacon! ---
**Author:** ![Casey1505](https://avatars.discourse-cdn.com/v4/letter/c/dc4da7/32.png) [@Casey1505](https://boards.straightdope.com/u/Casey1505)\ **Post date:** [December 19, 2002, 11:21pm UTC](https://boards.straightdope.com/t/gasoline-sheen-on-roast-beef/143784/17 "2002-12-19T23:21:16Z")
Gasoline Sheen? How many kids did that guy have, anyway? ---
**Author:** ![Popup](https://avatars.discourse-cdn.com/v4/letter/p/94ad74/32.png) [@Popup](https://boards.straightdope.com/u/Popup)\ **Post date:** [December 20, 2002, 8:54am UTC](https://boards.straightdope.com/t/gasoline-sheen-on-roast-beef/143784/18 "2002-12-20T08:54:53Z")
> [@](#): > > \*Originally posted by SandWriter \* > \*\*On the topic, what can you tell about meat by shining light on it, \*\* Quite a lot, by the look of the page I linked to earlier. Another page on the site describes how one can measure collagen content of meat, and thus estimate the toughness, using a fibre-optic probe. Pretty interesting!! [http://www.aps.uoguelph.ca/~swatland/rep235nr.htm](http://www.aps.uoguelph.ca/~swatland/rep235nr.htm) ---
**Author:** ![SandWriter](https://avatars.discourse-cdn.com/v4/letter/s/8491ac/32.png) [@SandWriter](https://boards.straightdope.com/u/SandWriter)\ **Post date:** [December 20, 2002, 2:18pm UTC](https://boards.straightdope.com/t/gasoline-sheen-on-roast-beef/143784/19 "2002-12-20T14:18:45Z")
> [@](#): > > \*Originally posted by Popup \* > \*\*using a fibre-optic probe. Pretty interesting!! [http://www.aps.uoguelph.ca/~swatland/rep235nr.htm](http://www.aps.uoguelph.ca/~swatland/rep235nr.htm) \*\* LOL. I love the picture at the start. possible captions… You should see what it does to a turkey! Talk or I’ll use my erector set gun on this hunk of meat. Hey Fred, let’s see what happens if we use it on a piece of meat. …