We eat a lot of salads and as part of that we make our own salad dressing.  As well as the normal vinegar and oil etc we like to add a crushed clove of garlic.  This flavours the dressing mildly garlicy but prevents getting chopped up bits of raw garlic into our salads, which none of us enjoy.  We'll often keep that clove in the bottom of the jar with a small remnant of dressing covering it and just keep topping up the oil and vinegar etc each day, and then replace the clove after 3 or 4 days.  We've been making homemade dressing like this for forever.

This last week though something odd has been happening.  The garlic clove is going a bluey turquoise colour overnight.  I have never had that happen before.   Its happened each time we made the dressing, and each time I have thrown it away the next day and started fresh.   All the other ingredients are the same and ones we have used before without this happening.

Anyone know what's going on, and are they OK to eat?    Pretty sure they are Chinese garlic bought from New World.