Question from Katy: I have a very simple question that I’ve been curious about for most of my life.
Why is milk white instead of some other color?
I know you can change the color of milk by adding stuff to it (chocolate syrup for example), but milk always comes out of the cow white. I know that for a fact because I grew up on a dairy farm.
Rick’s answer: That’s a great question, Katy. I’m certainly not a physicist but I’ll try to give you a simple layman’s answer.
The colors we see when we look at things depend on how well those things absorb the various wavelengths of light.
Things that absorb one or more wavelengths of light while reflecting the others will appear to be various colors depending on which actual wavelengths are absorbed and reflected.
Since the visible light spectrum contains a wide range of wavelengths our eyes see many different colors as we look at the things we encounter throughout the day.
If an object absorbs all wavelengths of light, that prevents any wavelengths from being reflected back into our eyes. Therefore, that object will appear to be black to the human eye.
Conversely, objects that don’t absorb any wavelengths at all appear white because every wavelength is reflected off the object and into our eyes.
Now, back to the question at hand…
Milk is approximately 90% water, and as you already know pure water is clear (so it basically has no color).
Therefore, it has to be the components that comprise the other 10% that give milk its distinctive white color.
The lactose, fats and proteins in milk work as a team to reflect all wavelengths of light while absorbing none.
That, in a nutshell, is why milk is white instead of some other color.
By the way, you mentioned above that you can change the color of milk by adding things to it. And that’s obviously true.
But truth be told, you can also change its color by removing one or more of its components.
You can verify that for yourself by placing glasses containing whole milk and skim milk side-by-side.
You’ll easily be able to see a difference in their colors (the skim milk will have a slight blueish tinge to it).
Now that we have the answer to your question out of the way, here’s a short video that dispels several common misconceptions about milk. Check it out!
Note: As always, you can watch the video at full screen by clicking the “square” icon that will pop up in the lower-right corner of the video after it begins playing.