I've only used it when something has been simmering or on a slow boil. I wisk in about 1/2 tsp per cup and find it it doesn't thicken right a way it seems to take a minute. The couple times I've used it I mixed it into the drippings from a roast before I added any water but the end result was still a fair bit thinner than when I've made gravy in the past using flour.