Homemade Yogurt

I've been making homemade yogurt for a while now. 3-3/4 cups water and 1-2/3 cups of instant non fat dry milk. Heat to 180 then cool to 115 then add culture cubes when it is 115. I just use this Styrofoam box with a lid to sit it in. Add two jars filled with hot tap water to the box and in about 6-8 hours it's ready. (Change out hot water jars after 4 hours) I bought some cultured yogurt at the store and put it in an ice-cube tray to freeze then pop them in a bag in the freezer. When I want to make yogurt I add 4 defrosted/room temperature cubes to my milk. It makes a thick, great tasting yogurt that is even better with a little honey in it and makes good smoothies.