Yogurt is easy to make at home. While special yogurt-making equipment allows for careful temperature control without a thermometer and reduces the chances of failure, you can use just about any glass or ceramic container and an ordinary cooler for temperature control. I use quart Mason jars and a cheap foam cooler.
You'll need a starter and fresh milk. I buy plain yogurt in the supermarket for starter and use Bonlac milk. Use locally produced yogurt and make sure it's not pasteurized. Here's the basic recipe.
quart whole milk - you can use 2% or skim milk
1 small plain Bonlac Yogurt
(Optional) I usually add 1/3 cup of powdered milk for a richer flavor
Bring milk just to a boil and then set aside to cool. This kills undesirable bacteria that might be present and also changes the properties of the milk protein so that it gives the yogurt a firmer body and texture. I use a candy thermometer to make sure the milk temperature does not exceed 212 degrees F. Let the milk cool to 115 degree F. Gently add the starter to the milk and stir, being careful not to mix in air.
I use a $2.00 foam cooler for an incubator. I added an incandescent light bulb (the bulb is mounted on a cheap table lamp fixture) and light dimmer. This allows me to maintain the temperature at 115 degrees F until the yogurt is properly cultured, but you can also heat water on the stove and pour the warm water into the cooler to maintain the temperature between 110 and 120 degrees F. Although it is possible to make yogurt at room temperature you will get more consistent results if you culture it at the recommended temperature. It should take about 3~4 hours to make, depending on the degree of tartness you want. I start checking after about 2 1/2 hours. You can spoon off a small amount to test texture and taste. Once the yogurt has the taste and texture you want, you can add fruit or flavoring to taste. Your yogurt should keep a week or more stored in the refrigerator.