On Saturday, I made purple mashed potatoes, see pc. They have a distinct purple color when fresh. However, when I went to put leftovers in my lunch this morning, they were very blue. This is the second time I've refrigerated leftovers and had a color change. The first time, I didn't really make a note of it, but now it's got me wondering... Why do purple mashed potatoes turn blue when you refrigerate them?
It's probably something to do with anthocyanins. We know they are heat-sensitive (cooked red cabbage or onions turn blue unless acid is added). Try adding a little wine or vinegar
next time you make purple mash and see what happens with the leftovers.
At least they stay purple through cooking. Purple string beans, sadly, turn green when cooked.
Anyone know if this is true for purple cauliflower?
In addition to acid, if they were held in an airtight environment they might stay more purple. You could cover them in a layer of fat like pate or confit.