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?
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.
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…
…
No blue. Now, it wasn’t a deep red wine…just some cheap soft red. But nothing went blue.
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!!!
You’re probably right — and this madsci.org post seems to back you up. The moral, I guess, is never listen to a physicist when the question deals with chemistry.
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
Well now that I’ve cracked open the red wine…
I’ll have to get a fresh glass.
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.
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
I’m referring to merlot, specifically.
<shrug> It’s from the Potomac.
Well, great. Now I’m going to have to go buy some merlot. Thanks a lot!
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.
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?
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.