Yes I made yogurt years ago.  You didn't love it then, so I eventually stopped. Then I discovered you like Nancy's Yogurt  
http://www.nancysyogurt.com/index.php/products 

I don't think most yogurt has preservatives.  The supermarket yogurt often is pasteurized so that the microbes stop fermentation.  Refrigeration helps slow fermentation down, but doesn't halt it completely. The sour flavor comes from the lactic acid produced by the Lactobacillus bulgaricus from the lactose in the milk.