Burrata is a type of cheese that is made from mozzarella and cream. The outside of the cheese is solid mozzarella, while the inside is a soft, creamy mixture. The creamy center should resemble a soft pillow when the cheese is cut open.  Some people believe that burrata should taste sour; however, this is not the case.  The sour taste comes from the lactic acid bacteria that are present in the milk used to make the cheese. These bacteria produce lactic acid, which gives burrata its characteristic tangy flavor.  However, lactic acid is not sour and should not be considered a flaw in the cheese. In fact, many people enjoy the unique taste of burrata.  If you are looking for a cheese with a sour taste, you may want to try another variety, such as Gorgonzola or Roquefort.