# Why is milk white? **URL:** \ **Category:** Factual Questions\ **Created:** [November 27, 2001, 1:33am UTC](https://boards.straightdope.com/t/why-is-milk-white/95415 "2001-11-27T01:33:02Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![bbs2k](https://avatars.discourse-cdn.com/v4/letter/b/e495f1/32.png) [@bbs2k](https://boards.straightdope.com/u/bbs2k)\ **Post date:** [November 27, 2001, 1:33am UTC](https://boards.straightdope.com/t/why-is-milk-white/95415/1 "2001-11-27T01:33:02Z")
I came across a question so simple that I’m stumped. Why is milk white? Is it the casien? PS… Chocolate milk doesn’t count wise-guys ---
**Author:** ![bbs2k](https://avatars.discourse-cdn.com/v4/letter/b/e495f1/32.png) [@bbs2k](https://boards.straightdope.com/u/bbs2k)\ **Post date:** [November 27, 2001, 2:04am UTC](https://boards.straightdope.com/t/why-is-milk-white/95415/2 "2001-11-27T02:04:48Z")
c’mon guys, someone has to have an answer ---
**Author:** ![DrFidelius](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/drfidelius/32/3447_2.png) [@DrFidelius](https://boards.straightdope.com/u/DrFidelius)\ **Post date:** [November 27, 2001, 2:12am UTC](https://boards.straightdope.com/t/why-is-milk-white/95415/3 "2001-11-27T02:12:39Z")
Keep your shirt on. We are not here to drop everything and answer non-questions. Casien in solution reflects white light. You knew this already. ---
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [November 27, 2001, 2:51am UTC](https://boards.straightdope.com/t/why-is-milk-white/95415/4 "2001-11-27T02:51:05Z")
Actually, I thought it was due, at least in part, to the milk fat. Phrased differently, **blood** with high levels of fat in it (similar to that found in milk) looks white, like milk. [Here’s an example](http://www.mednet.gr/pim/l6.htm). ---
**Author:** ![DrFidelius](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/drfidelius/32/3447_2.png) [@DrFidelius](https://boards.straightdope.com/u/DrFidelius)\ **Post date:** [November 27, 2001, 2:57am UTC](https://boards.straightdope.com/t/why-is-milk-white/95415/5 "2001-11-27T02:57:50Z")
I’m sticking with the proteins, as fat-free milk is still white. Milk fats seem to be more yellowish. ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [November 27, 2001, 3:01am UTC](https://boards.straightdope.com/t/why-is-milk-white/95415/6 "2001-11-27T03:01:10Z")
DrFidelius and KarlGauss you’re both right. [Why is Milk white?](http://www.uselessknowledge.com/explain/milk.shtml) FWIW bigbabysweets2000 finding this info. took approximately 2 seconds via google asking “Why is milk white?”. Before you ask the teeming millions next time try [http://www.google.com](http://www.google.com) first, it’s a great search tool. Welcome onboard. ---
**Author:** ![bbs2k](https://avatars.discourse-cdn.com/v4/letter/b/e495f1/32.png) [@bbs2k](https://boards.straightdope.com/u/bbs2k)\ **Post date:** [November 27, 2001, 3:53am UTC](https://boards.straightdope.com/t/why-is-milk-white/95415/7 "2001-11-27T03:53:26Z")
dude… i tried… I already was pretty sure that the answer was casien, but I’ve found a lot of stupid stuff on the net before, so I figured I’d bring it to the big boy arena to settle this one out. ---
**Author:** ![Bob\_Scene](https://avatars.discourse-cdn.com/v4/letter/b/e19adc/32.png) [@Bob\_Scene](https://boards.straightdope.com/u/Bob_Scene)\ **Post date:** [November 27, 2001, 6:13am UTC](https://boards.straightdope.com/t/why-is-milk-white/95415/8 "2001-11-27T06:13:01Z")
From: [http://www.uselessknowledge.com/explain/milk.shtml](http://www.uselessknowledge.com/explain/milk.shtml) > [@](#): > > the cream that is found in milk contains white colored fat… The molecules that make up Casein and cream reflect light. That’s why milk is white. I guess that’s not **quite** as stupid as the “why glass is clear” bullshit from [howstuffworks.com](http://howstuffworks.com), but it’s still wrong. Fat molecules and casein molecules don’t reflect any significant amount of visible light. If you had a crystal of **pure** casein or a homogeneous sample of **pure** milk fat, it would be transparent. Milk is white and opaque because it’s an **emulsion,** not a solution. Casein and fat in milk are present in the form of [micelles](http://www.foodsci.uoguelph.ca/deicon/casein.html) that **scatter** light because they have a different refractive index from the water they’re suspended in. Every time a light ray passes from the water into a micelle or vice-versa, it gets bent a little because of the refractive index difference. The effect of having millions of micelles floating around is that every ray of light ends up going in a different direction because of being bent so many times. So when light hits milk it leaves the milk traveling in all different directions, making the milk look white. The same effect is what makes clouds and paint white, even though they’re made of clear substances. ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [November 27, 2001, 6:29am UTC](https://boards.straightdope.com/t/why-is-milk-white/95415/9 "2001-11-27T06:29:45Z")
> [@](#): > > \*Originally posted by Bob Scene \* > \*\*From: > > [http://www.uselessknowledge.com/explain/milk.shtml](http://www.uselessknowledge.com/explain/milk.shtml) > > > [@](#): > > > > the cream that is found in milk contains white colored fat… The molecules that make up Casein and cream reflect light. That’s why milk is white. > > I guess that’s not **quite** as stupid as the “why glass is clear” bullshit from [howstuffworks.com](http://howstuffworks.com), but it’s still wrong. > > Fat molecules and casein molecules don’t reflect any significant amount of visible light. If you had a crystal of **pure** casein or a homogeneous sample of **pure** milk fat, it would be transparent. > > Milk is white and opaque because it’s an **emulsion,** not a solution. Casein and fat in milk are present in the form of [micelles](http://www.foodsci.uoguelph.ca/deicon/casein.html) that **scatter** light because they have a different refractive index from the water they’re suspended in. Every time a light ray passes from the water into a micelle or vice-versa, it gets bent a little because of the refractive index difference. The effect of having millions of micelles floating around is that every ray of light ends up going in a different direction because of being bent so many times. So when light hits milk it leaves the milk traveling in all different directions, making the milk look white. The same effect is what makes clouds and paint white, even though they’re made of clear substances. \*\* But IIRC 2% is “whiter” than skim and whole milk is a little “whiter” than 2%. If fat levels are the main difference between these types of milk how can you say the percent of fat in the milk has no effect? ---
**Author:** ![Bob\_Scene](https://avatars.discourse-cdn.com/v4/letter/b/e19adc/32.png) [@Bob\_Scene](https://boards.straightdope.com/u/Bob_Scene)\ **Post date:** [November 27, 2001, 7:10am UTC](https://boards.straightdope.com/t/why-is-milk-white/95415/10 "2001-11-27T07:10:29Z")
Did I say the percent has no effect? I don’t think I did. Of course the percent has an effect. ---
**Author:** ![Popup](https://avatars.discourse-cdn.com/v4/letter/p/94ad74/32.png) [@Popup](https://boards.straightdope.com/u/Popup)\ **Post date:** [November 27, 2001, 10:06am UTC](https://boards.straightdope.com/t/why-is-milk-white/95415/11 "2001-11-27T10:06:44Z")
> [@](#): > > \*Originally posted by astro \* > \*\*But IIRC 2% is “whiter” than skim and whole milk is a little “whiter” than 2%. If fat levels are the main difference between these types of milk how can you say the percent of fat in the milk has no effect? \*\* Yup, but that doesn’t mean that **Bob** ’s wrong. One interesting experiment to try at home is to mix milk and water. If you only add a litle milk to the water it looks bluish. That’s because the light gets **scattered** , and diferent wavelengths react differently. The shorter wavelengths (blue) scatter more easily, and the milk looks bluish. On the other hand the longer wavelengths (red) don’t scatter as easily and if you look at the transmitted light it will have a yellow/red hue.