I was reading a new canning book today (Blue Chair Preserving) and the author recommends sterilizing jars and lids for canning jam by heating them in a 250 degree oven for 30 minutes. That seems safe enough, but then she also recommends using a hot oven to seal the jars. Has anyone done this? Is it safe and effective? What about for tomato products or pickled foods (anything you'd normally do in a standard water bath canner)? It's intriguing as my canning rack causes some issues and I'm seeking a better one that keeps jars actually in their rightful place. Also could be good for odd-sized batches.