My project started off with the selection of the main ingredient, milk. I chose to go with a tasty grass fed raw milk from a vendor at my local farmer's market. While I used raw milk for this, yogurt can be made with any kind of milk, pasteurized skim, low fat, whole, cow, goat,etc.
To begin, I placed a quart of milk in a stainless steel crock, and placed that inside another larger pot filled with a bit of water on the stove. This was done to create a double boiler effect to some extent. Basically you want to be able to heat the milk without scalding with direct heat of your stove flame of burner.
Next, I heated my milk up to about 180 degrees F to pasteurize it and create a clean slate for the yogurt cultures to ferment the milk. This was a step mentioned in most of the recipes, though I am not totally sure it is needed. Reasons being, on one hand you have clean raw milk, that if collected and handled in a sanitary manner, is very safe and contains enzymes and other naturally occurring biological components that aid in it's microbial stability. On the other hand, you have a pasteurized milk product that has been heat-treated to kill pathogens that might occur from contamination prior to packaging. I am not sure I will employ this heat step next time.
After I heated my milk, I immediately cooled it down to about 120 degrees F in a cool water bath (drain hot water from larger boiler pot, and fill with cool water from the tap). At this point it was time to add my starter to introduce the live cultures that would ferment the milk. I stirred in about 1/2 cup of commercial low fat yogurt purchased from my local grocery store.
After six hours the yogurt had firmed up, signaling to me that the fermentation was finished. I covered the crock with some plastic wrap and placed it in the refrigerator overnight.
Though it was a lengthy process, I can easily see myself doing this more often. Outside of the initial heating and mixing, most of the production time involves no effort, and the results are well worth it!