I used an inexpensive combination of a standard crock pot and a Dorkfood Sous Vide controller.
Using these instructions you can make yogurt from skim, part skim or even whole milk.
It's easy and cheap and you totally control the ingredients.
Step 1: Equipment & Ingredients You Will Need
• Crock Pot with an analog switch. You cannot use crock pots with electronic controls because the sous vide controller controls the temperature by turning the electricity on and off. If you would reset the controls to your crock pot by cycling the power, this won't work. I used this from Amazon ($20.99) Crock-Pot SCR300SS 3-Quart Round Manual Slow Cooker, Stainless Steel http://www.amazon.com/gp/product/B003UCG8II?psc=1&...
• Sous-Vide control. I used the Dorkfood Sous-Vide Temperature Controller (DSV) (Also from Amazon - $99.00). http://www.amazon.com/gp/product/B0088OTON4?psc=1&... This has a temperature probe, a digital read-out and has an outlet that you plug the Crock Pot into.
• Jars for yogurt. This can be just about any container that can stand to be heated to 120 degrees. I use glass mason jars. The height of the jar must be at least one inch below the height of the Crockpot so that the entire jar can be submerged in the water bath.
• Spoon for stirring the yogurt.
• Thermometer to measure the temperature of the milk.
• Pyrex cup to heat milk in the microwave.
• Three cups of milk. I prefer whole milk but anything from skim to Half-And-Half will work
• One Quarter Cup of Plain yogurt with LIVE yogurt cultures. I've successfully used vanilla yogurt too. You can reuse some of your home-made yogurt. I've done this for three generations of yogurt. I'm unsure if the culture would ever become "too old" to reuse.
Step 2: Clean and Sterilize Everything
• You don't want your yogurt to compete with any other bacteria so wash rinse and then use boiling water to scald everything that will come into contact with the yogurt.
Step 3: Heat Your Milk to 180 Degrees, Fahrenheit.
• Put the quart of milk into the sterilized Pyrex cup. heat in the microwave testing the temperature once a minute.
• Keep stirring the milk every minute or so to insure an even temperature.
• Once the milk is at 180 keep it at that temperature for 10 minutes and then cover and let the temperature drop to 120 degrees. Some people put the pot in an ice bath to accelerate the process.
Step 4: Combine Milk With Yogurt Starter
• Put half the yogurt into each container.
• When the milk is 120 degrees, stir the milk into the yogurt thoroughly
• Screw the tops on until just tight
Step 5: Set the Sous Vide to 110-115 Degrees and Incubate the Yogurt 8 to 12 Hours.
• Make sure that every jar is completely submerged by at least one inch of water.
• Leave the yogurt in the sous vide for 8 to 12 hours. The longer it sits the firmer and tangier it becomes.
• Don't worry if there is a green-tinted liquid on top of the yogurt. This is normal.
• The yogurt should be firm and smell fresh.
• Refrigerate the yogurt immediately. It will thicken somewhat as it chills.
• Yogurt will store for at least 10 days.