Making Homemade Yogurt

A friend recently asked me for this recipe so I decided to post it here so anyone else can have access to it.I got the instructions from a book Titled Super Baby Food by Ruth Yaron. Our pediatrician recommended this book when Rafi started eating solids. It has been a huge help. It has recipes and ideas on how to make your own baby food and even ideas for children crafts.
Ok, so here are the steps on how to make homemade yogurt.

1. Sterilize the Milk to kill all the bacteria: Nest a thick, sturdy, heat proof glass jar with the milk into a pot of water on the stove top and bring it to a boil.  Keep a yogurt or candy thermometer submerged in the milk at least 2 inches to watch the temperature.  It should not rise above 185 degrees F.  It should be between 180 and 185 degrees F.  I use the nested glass jar method to save having to clean the large pot plus you can use the large pot of boiled water to sterilize utensils you will use to mix the starter to the sterilized milk later.
2. Cool the Milk to Incubation Temperature - about 112 degrees F:  You can cool it at room temperature or cool it in the refrigerator.  Keep the thermometer submerged and watch the temperature.  It needs to be no higher than 120 degrees F but the closer it stays between 105 and 110 degrees F the better.  In my refrigerator it takes about an hour and five mins to cool down to 112 degrees F.  Keep a spoon in the milk for frequent stirring to evenly distribute the heat.  Optionally, you may add Nonfat Dry Milk Powder at this time to thicken the consistency of the yogurt and add nutritional content.  Add about 1/4 cup powder per quart of cooled milk and mix very well.
3. Add the Starter:  You can use yogurt bought at the store.  Make sure it says it contains live and active cultures.  Make sure the yogurt is not too old.  For each quart of cooled milk, gently fold in about 2 tablespoons of yogurt.  Another starter is freeze dried bacteria culture sold in packets at any natural food store.  This starter is more expensive but also more reliable.
4. Incubate Yogurt and let the Cultures Grow: Cover the yogurt during incubation so it is not open to the air which always contains bacteria.  Use the cover of the jar or use a plastic wrap over the jar.  Keep the yogurt warm during incubation.  The bacteria grows when it is neither too cold or too hot.  Keep the temperature between 105 and 112 degrees F.  I use a hot pot of water on the stove top to keep the yogurt warm.  I keep an eye on the thermometer to make sure the temperature stays right.  Other places the author suggests are Conventional oven, the kitchen sink with warm water half way up the jar, an electric fry pan, a crockpot, a warming tray, a heating pad, a home heating source (like a radiator, wood stove or heating duct), a major appliance (like a TV, stereo, or other electronic equipment), microwave safe neck warmers, an electric commercial yogurt maker, . . . anywhere warm!!  
5. Keep the yogurt still during incubation: Place the jar with the yogurt mixture where it won't be disturbed for a few hours.  It will take several hours for the yogurt to become thick and pudding like.  Anywhere from 4 to 12 hours.  Mine usually takes about 5 or 6 hours.  
6. Refrigerate the finished product:  Cover and refrigerated the finished yogurt for several hours before serving.  The yogurt will keep in the refrigerator for about 1 to 2 weeks.  If you will use some of this batch to make the next one make sure it is no older than 5 to 7 days.  

You will need to experiment a couple of times or more until you get it right.  I had to find the right amount of time to let it cool and the right method to keep it warm.  I tried the new warmer and it didn't work very well for me.  I found that using the hot pot of water works better for me but I had to baby sit it to make sure the water was not too hot.
I hope this helps.  If you need additional information please email me and let me know.  The book has a more detailed explanation.  I gave here what I know works for me.

Have fun!!
Tania