I am here to tell you that freedom from the hegemony of the non-recyclable plastic yogurt container is not only possible, but you will also save money in the process of throwing off those hegemonic chains when you make your own yogurt at home. All told, it takes perhaps 20 minutes to make 2 quarts of yogurt and requires a just few things you probably have in your kitchen right now. Namely: a pot for heating the milk, a thermometer, and a spoon, plus a low-cost incubation setup.
I have made yogurt several times now in a homemade setup that cost me zero money and zero time spent on Craig's list looking for a used yogurt maker. It consists of a small cooler, a plastic container (or containers) that fit in the cooler, a bath towel, and one of those rice-hull pillows that you heat up in the microwave. Once the milk has been heated, cooled and mixed with the starter, I heat the rice-hull pillow for 2 minutes, put it in the bottom of the cooler, put in the container with the milk, and then stuff in a clean, dry bath towel to help hold the heat. Then close it up for 8-14 hours.
Each time I open the cooler I feel like I just pulled a rabbit out of my hat when I take out that container and find the milk I put in hours before has indeed jelled into thick creamy yogurt.
Here is one secret - remember this because it will become important later: To make yogurt, you have to have a little yogurt already - this provides the bacterial culture that will make your new bottle of milk into new yogurt. However, it's not very handy or cost effective if you have to buy yogurt in order to make yogurt every time. But Diana told me a trick: you can freeze yogurt in ice cube trays to use as your starter. Take a cube or two out and thaw just before making a new batch.
Yogurt, like sauerkraut, is a lacto-fermented food that depends on the introduction of live cultures and a process of bacterial activity that denatures milk proteins and increases its acidity to form the tangy curd that is yogurt. The cultured bacteria eat the sugars (lactose) in milk and poop out lactic acid. I think that's why people who are lactose intolerant can eat yogurt (the lactose has already been digested by bacteria) and also why it's called "lacto-fermentation." Like those in sauerkraut, the live cultures in yogurt are supposed to be good for your gut.
WikiP says: "There is evidence of cultured milk products being produced as food for at least 4,500 years. The earliest yoghurts were probably spontaneously fermented by wild bacteria living on the goat skin bags carried by nomadic people. Today, many different countries claim yoghurt as their own invention, yet there is no clear evidence as to where it was first discovered.
Yoghurt is made by introducing specific bacteria strains into milk, which is subsequently fermented under controlled temperatures and environmental conditions (inside a bioreactor), especially in industrial production. The bacteria ingest natural milk sugars and release lactic acid as a waste product. The increased acidity causes milk proteins to tangle into a solid mass (curd) in a process called denaturation. The increased acidity (pH=4–5) also prevents the proliferation of potentially pathogenic bacteria."
Yogurt Directions from Wikipedia (I have been using this process)
1. Sterilize the milk. Even though your milk has been pasteurized, it will still contain bacteria. Pour a quart (I use a half gallon - we eat a lot of yogurt) of milk into a pot or the top of a double boiler. Use a metal spoon for stirring. Heat the milk until it is almost boiling. You'll see small bubbles form around the edges and steam beginning to rise. Keep checking the temperature: It should be around 180-185F (82-85C). A candy thermometer comes in handy. Heat slowly and stir often to prevent scorching.
2. Cool the milk to grow the yogurt. Allow the milk to cool at room temperature or in the refrigerator. Stir frequently to make temperature checks more accurate. Don't proceed until the milk is below 120F(49C), and don't allow it to go below 90F (32C). 105-110 (41-43) is optimal.
3. Warm the starter. Let the starter yogurt sit at room temperature while you are waiting for the milk to cool. This will prevent it from being too cold when you add it in.
4. Add nonfat dry milk, if desired. Adding about 1/4cup to 1/2 cup nonfat dry milk at this time will increase the nutritional content of the yogurt. The yogurt will also thicken more easily. This is especially helpful if you are using nonfat milk. (I don't add non-fat dry milk).
5. Add the starter. Add 2 tablespoons of existing yogurt, or add the freeze-dried bacteria.
6. Put the mixture in containers. Pour your milk into a clean container or containers. Cover each one tightly with a lid or plastic wrap.
7. Allow the yogurt bacteria to incubate. Keep the yogurt warm to encourage bacteria growth. Between 105F and 122F (41C and 49C) is ideal. An oven with pilot light is one option; see Tips for others. Use your candy thermometer to check on the temperature. Wait until the yogurt is thick, about the consistency of pudding. Keep the yogurt still during this process. It can take anywhere from 8-14 hours to incubate. (Consider starting your yogurt in the morning....)
8. Refrigerate the yogurt. Place the yogurt in your fridge for several hours before serving. It will keep for 1-2 weeks. If you are going to use some of it as starter, use it within 5-7 days, so that the bacteria still have growing power. Whey, a thin yellow liquid, will form on the top. You can pour it off or stir it in before eating your yogurt.
9. Use yogurt from this batch as starter for the next batch.
Do I even need to mention that homemade yogurt is especially good with homemade granola? And with the raspberry and apricot preserves I made, it's dreamy. It also makes very fine yogurt cheese, which I frequently substitute for sour cream. All this for the price of a 1/2 gallon of Calder milk. I know Laura Ingalls would be proud of me.