Commercial yogurt often has added gelatin & thickeners (often along with some chemical nasties I'm afraid.) The taste of the homemade yogurt can't be beat, is significantly cheaper and healthier for you. And no more plastic yogurt containers go to the landfill!
Cool milk down to about 105 to 110 degrees. Add yogurt starter and stir well to incorporate smoothness. (if making sweet yogurt, add vanilla now).
Fill glass containers of your choice and place lids on jars. Place jars on cookie sheet. Heat oven to 110-115 and turn off oven temp. Turn on oven light. Place yogurt in oven on rack and leave for about 4-6 hrs.
Yogurt will be "done" in 4-6 hours but you can let it incubate for up to 12 depending on how tart you like it and how much beneficial cultures you wish it to have.
It will firm a little more upon cooling, although it's a more silky yogurt than the ones in the store since they add gelatin & thickeners to the commercial stuff (often along with some chemical nasties I'm afraid.)