Not usually. All natural stone is porous to some extent but granite has a very low porosity. Sealers are used to further reduce the porosity and the chance of staining. Different types of granite can have different porosity levels. Sealers are used during the installation process the prevent liquids from immediately penetrating the stone and staining it. It is possible for dark liquids such as red wine or oily products to leave a stain if left to penetrate the granite (usually over several hours). Should this happen, poultice kits can be purchased. A poultice is a paste like substance that is applied to the granite then covered with plastic and allowed to sit to draw the stain out of the granite and into the paste.