I've read never to simmer yogurt as it will seperate. I'd already confirmed this independently with a couple of Indian recipe disasters. However, I constantly see recipes that have you bring yogurt to a simmer. There's one for chicken curry in the new Food and Wine that instructs you to do this. What's the deal here? Are the recipes wrong, does it apply to only certain types of yogurt, can you only simmer it for a short time, or what?