I got this original recipe from  http://www.lynnskitchenadventures.com/2009/08/easy-homemade-berry-yogurt.html#respond.  I have altered it some to suit our tastes.

Homemade Flavored Yogurt ( leave the jelly out if you want plain yogurt)

• 4  3/4 cups milk at room temperature ( do not use fat free milk, it does not work well)
• 8 ounces of high quality plain yogurt (yes this is more than most recipes, but it works)
• 10 tablespoons of powdered milk
• For flavored yogurt use:
• 1/4 cup of jelly or jam or 1/2 cup pureed sweetened fruit (I have frozen fruit already sweetened that we picked this summer)

Milk must be at room temperature!  I measure it out and place it in a bowl that is covered for a few hours or heat milk to 180 degrees then cool to between 100 and 110 degrees.   Once the milk is at room temperature mix together the remaining ingredients(these need to be room temperature as well) , including the jelly or pureed fruit  . I find this mixes together best in a blender.  I let mine sit for a while after blending as I did not want frothy yogurt.    But if you are just making plain yogurt you can mix together with a whisk.  I then fill my yogurt cups and heat for 12 hours. Yogurt makers are different.  Adjust time according to your maker.   Remove jars from yogurt maker, refrigerate, and enjoy.