# Why does red wine turn blue when diluted? **URL:** \ **Category:** Factual Questions\ **Created:** [August 21, 2011, 2:11am UTC](https://boards.straightdope.com/t/why-does-red-wine-turn-blue-when-diluted/593493 "2011-08-21T02:11:39Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![Johanna](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johanna/32/8318_2.png) [@Johanna](https://boards.straightdope.com/u/Johanna)\ **Post date:** [August 21, 2011, 2:11am UTC](https://boards.straightdope.com/t/why-does-red-wine-turn-blue-when-diluted/593493/1 "2011-08-21T02:11:39Z")
A glass with 2 or 3 drops of red wine in it. Fill it with water. No more red—it’s blue! How on earth? ---
**Author:** ![MikeS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MikeS](https://boards.straightdope.com/u/MikeS)\ **Post date:** [August 21, 2011, 2:35am UTC](https://boards.straightdope.com/t/why-does-red-wine-turn-blue-when-diluted/593493/2 "2011-08-21T02:35:22Z")
I don’t have a bottle of red wine around to investigate this myself (more’s the pity), but my first guess would be [Rayleigh scattering](http://en.wikipedia.org/wiki/Rayleigh_scattering). ---
**Author:** ![kittenblue](https://avatars.discourse-cdn.com/v4/letter/k/ba8739/32.png) [@kittenblue](https://boards.straightdope.com/u/kittenblue)\ **Post date:** [August 21, 2011, 2:52am UTC](https://boards.straightdope.com/t/why-does-red-wine-turn-blue-when-diluted/593493/3 "2011-08-21T02:52:45Z")
I was just about to crack open a bottle of wine…lol…oh, wait…there are five drops left in the bottle in the recycling bin! Let me go test this out… … ---
**Author:** ![kittenblue](https://avatars.discourse-cdn.com/v4/letter/k/ba8739/32.png) [@kittenblue](https://boards.straightdope.com/u/kittenblue)\ **Post date:** [August 21, 2011, 2:59am UTC](https://boards.straightdope.com/t/why-does-red-wine-turn-blue-when-diluted/593493/4 "2011-08-21T02:59:14Z")
No blue. Now, it wasn’t a deep red wine…just some cheap soft red. But nothing went blue. ---
**Author:** ![Sigene](https://avatars.discourse-cdn.com/v4/letter/s/df788c/32.png) [@Sigene](https://boards.straightdope.com/u/Sigene)\ **Post date:** [August 21, 2011, 3:28am UTC](https://boards.straightdope.com/t/why-does-red-wine-turn-blue-when-diluted/593493/5 "2011-08-21T03:28:09Z")
I’m prettysure it isn’t Rayleigh scattering. I’m inclined to think its due to a change in pH. It is a fairly common occurance that vegetable dyes change color due to pH changes. I’ve seen this in wine myself. I have NOT tried to specifically add a base or acid to the wine to intentionally make it change color. I’m going to guess that the wine is slightly acidic and red, but turns blue when pH is increased towards the basic range. I have some wine and some sodium hydroxide…TO THE LAB!!! ---
**Author:** ![MikeS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MikeS](https://boards.straightdope.com/u/MikeS)\ **Post date:** [August 21, 2011, 3:35am UTC](https://boards.straightdope.com/t/why-does-red-wine-turn-blue-when-diluted/593493/6 "2011-08-21T03:35:46Z")
> [@Sigene](#): > > I’m prettysure it isn’t Rayleigh scattering. > > I’m inclined to think its due to a change in pH. It is a fairly common occurance that vegetable dyes change color due to pH changes. I’ve seen this in wine myself. You’re probably right — and [this madsci.org post](http://www.madsci.org/posts/archives/2001-04/987512428.Ch.r.html) seems to back you up. The moral, I guess, is never listen to a physicist when the question deals with chemistry. ---
**Author:** ![Sigene](https://avatars.discourse-cdn.com/v4/letter/s/df788c/32.png) [@Sigene](https://boards.straightdope.com/u/Sigene)\ **Post date:** [August 21, 2011, 3:38am UTC](https://boards.straightdope.com/t/why-does-red-wine-turn-blue-when-diluted/593493/7 "2011-08-21T03:38:58Z")
RESULTS: A little red wine (Cabernet in a box) diluted a bit…because the first time it was too intense to make out a change. Added NaOH. the crystals fell to the bottom of the glass and appeared to give off a dark blackish blue trail as they fell. swirl to dissolve crystals Glass of wine turned a VERY intense VERY dark blue/black. Conclusion: Hypothesis supported. the color change seems to be dependent on a change in pH. Specifically when the wine is turned basic, it’s color changes to dark blue or even black ---
**Author:** ![Sigene](https://avatars.discourse-cdn.com/v4/letter/s/df788c/32.png) [@Sigene](https://boards.straightdope.com/u/Sigene)\ **Post date:** [August 21, 2011, 3:41am UTC](https://boards.straightdope.com/t/why-does-red-wine-turn-blue-when-diluted/593493/8 "2011-08-21T03:41:04Z")
Well now that I’ve cracked open the red wine… I’ll have to get a fresh glass. ---
**Author:** ![bump](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bump](https://boards.straightdope.com/u/bump)\ **Post date:** [August 21, 2011, 3:43am UTC](https://boards.straightdope.com/t/why-does-red-wine-turn-blue-when-diluted/593493/9 "2011-08-21T03:43:40Z")
Anthocyanin pigments are purple/red in acidic solutions, and blue in basic ones. The same thing happens with red cabbage, by the way. Your water must be pretty hard if it’ll turn red wine blue. ---
**Author:** ![user\_hostile](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/user_hostile/32/474_2.png) [@user\_hostile](https://boards.straightdope.com/u/user_hostile)\ **Post date:** [August 21, 2011, 4:39am UTC](https://boards.straightdope.com/t/why-does-red-wine-turn-blue-when-diluted/593493/10 "2011-08-21T04:39:15Z")
Aha! I notice when I rinsed the Merlot in a white sink the color of the wine turned blue. The water softener used is a potassium salt. Better living through chemistry1 ---
**Author:** ![Johanna](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johanna/32/8318_2.png) [@Johanna](https://boards.straightdope.com/u/Johanna)\ **Post date:** [August 21, 2011, 5:24am UTC](https://boards.straightdope.com/t/why-does-red-wine-turn-blue-when-diluted/593493/11 "2011-08-21T05:24:10Z")
> [@kittenblue](#): > > No blue. Now, it wasn’t a deep red wine…just some cheap soft red. But nothing went blue. I’m referring to merlot, specifically. > [@bump](#): > > Your water must be pretty hard if it’ll turn red wine blue. \ It’s from the Potomac. ---
**Author:** ![kittenblue](https://avatars.discourse-cdn.com/v4/letter/k/ba8739/32.png) [@kittenblue](https://boards.straightdope.com/u/kittenblue)\ **Post date:** [August 21, 2011, 1:20pm UTC](https://boards.straightdope.com/t/why-does-red-wine-turn-blue-when-diluted/593493/12 "2011-08-21T13:20:13Z")
Well, great. Now I’m going to have to go buy some merlot. Thanks a lot! ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [August 21, 2011, 2:44pm UTC](https://boards.straightdope.com/t/why-does-red-wine-turn-blue-when-diluted/593493/13 "2011-08-21T14:44:44Z")
This happens with pretty much any red wine. And pretty much any water. I’d always wondered about the the mechanism, but suspected that, like litmus paper, it was pH related. Good to see that confirmed. If you let the red wine evaporate the effect seems stronger. e.g. Drink a glass of wine. leave the glass sitting on the counter overnight with that last couple of drops in the bottom. The next day (once fully awake), put a 1/2" or so of water in the glass & swirl. the result is light blue water. If you fill the glass full of water the color will be too light to distinguish from ordinary water. ---
**Author:** ![Johanna](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johanna/32/8318_2.png) [@Johanna](https://boards.straightdope.com/u/Johanna)\ **Post date:** [August 21, 2011, 6:31pm UTC](https://boards.straightdope.com/t/why-does-red-wine-turn-blue-when-diluted/593493/14 "2011-08-21T18:31:05Z")
> [@LSLGuy](#): > > If you let the red wine evaporate the effect seems stronger. e.g. Drink a glass of wine. leave the glass sitting on the counter overnight with that last couple of drops in the bottom. The next day (once fully awake), put a 1/2" or so of water in the glass & swirl. the result is light blue water. If you fill the glass full of water the color will be too light to distinguish from ordinary water. Yeah. Thank you. That was the detail I omitted. Wineglasses left out all night and washed the following day is where I always observe the phenomenon. Now what could be the reason for the color getting stronger that way? ---
**Author:** ![ultrafilter](https://avatars.discourse-cdn.com/v4/letter/u/3d9bf3/32.png) [@ultrafilter](https://boards.straightdope.com/u/ultrafilter)\ **Post date:** [August 21, 2011, 6:51pm UTC](https://boards.straightdope.com/t/why-does-red-wine-turn-blue-when-diluted/593493/15 "2011-08-21T18:51:06Z")
> [@Johanna](#): > > Yeah. Thank you. That was the detail I omitted. Wineglasses left out all night and washed the following day is where I always observe the phenomenon. Now what could be the reason for the color getting stronger that way? Water evaporating? ---
**Author:** ![Johanna](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johanna/32/8318_2.png) [@Johanna](https://boards.straightdope.com/u/Johanna)\ **Post date:** [August 22, 2011, 5:48am UTC](https://boards.straightdope.com/t/why-does-red-wine-turn-blue-when-diluted/593493/16 "2011-08-22T05:48:35Z")
> [@ultrafilter](#): > > Water evaporating? The phenomenon happens with dilution, not evaporation. I don’t get why first evaporating the few drops of wine would make a stronger color when later diluted.