Before century, all leavened bread was sourdoughbread, since they thought it was the yeast giving the bread the sour taste. Today we are able to produce yeast without lactobacillus which actually gives the sour taste.
If you have to choose what part of your house should be impeccably clean, it should be your bathroom. Kitchens should be clean, too, but they get easily messy, because of all the cooking and eating. The good news is that you can keep your bath.