I made a salad dressing with olive oil, apple cider vinegar, garlic cloves chopped into halves, fresh ginger, mixed herbs and mustard powder. When the dressing was finished I put a lidded jar of it in the fridge, and two days later topped it up again with fresh ingredients.

The following day the garlic from the original batch had turned bright blue. Why?

Ellice Bourke, Katherine, Northern Territory, Australia