We recently had an interesting enquiry from a customer, when their red wine turned blue!
They were rinsing their wine glass that contained residual red wine with some tank water, and upon contact the water and the residual wine in the glass turned blue.
This phenomenon is easily explained with chemistry. Wines are generally acidic, with a pH around 3-4. In red wine, the red colour comes from pigment in grape skins called anthocyanin. Anthocyanins are water soluble vacuolar pigments that may appear red, purple or blue, depending on its pH. Therefore, they also function as an acid base indicator as the colour changes with the pH. This is the same chemistry behind the litmus paper for pH test.
When we tested the tank water used for rinsing, the water was highly alkaline (pH >10). The water was stored in a new concrete tank, and is likely to been impacted by leached lime from the concrete, causing the water to be highly alkaline. When mixed with the acidic red wine residue, the water turned blue due to presence of anthocyanins, indicating an alkaline condition.
There is a simple test you can do at home to observe this condition, by mixing bicarbonate soda into red wine, and observe if the colour of the wine will blue. This is also handy in removing red wine stain.
Red wine or Blue wine? was originally seen on: http://sesl.com.au/
SESL Australia 