If you are having difficulty with gummy centers or under-baked bread, I would suggest that you get an oven thermometer to test the actual baking temperature of your oven. For example, I recently traveled for a trade show and the oven I used, a fairly new one, was off by 30 degrees when I tested it with a thermometer. Thus, I had to set it to 380 degrees to get the oven to bake at 350 degrees. This is a very common issue and can result in bread that does not bake all the way through. Any standard oven thermometer should do. They are inexpensive and well worth the minimal investment!