It was a brave woman, who decided to taste the strangely thickened stuff that appeared in her milk container one day. I wonder how our early ancestors figured out the difference between “spoiled” milk that was safe and even good for you, like yogurt, and the kind that can kill you? Sounds like a dangerous game to me.
Yogurt seems to have originated in Central Asia at least 4,500 years ago. No one knows how it was created the first time, but it was most likely an accident. With no refrigeration, milk was something that had to be consumed as soon as it was drawn from its animal source. This was true even during the cooler seasons of the year because with no pasteurization, milk is a prime medium for the growth of undesirable bacteria that can kill. However, some of the bacteria floating around can have a good effect when they colonize our food. Think about the wild yeast beers made in Belgium, or those fabulous French cheeses. Along with yogurt, these foods were likely discovered by accident when wild bacteria came to call. The creation of yogurt and cheeses allowed us to preserve milk for a little longer, a real boon to ancient nutrition, not to mention, tasty.
Humans are supremely adaptable, and after a while we figured out how to ensure the good kind of “spoiled” milk every time we tried to make it. Lucky for us, we don’t have to do this through trial and error they way our ancestors did, we’ve got science! Yogurt is milk that has been cultured with two (and sometimes more) bacteria, Lactobacillus bulgaricus and Streptococcus thermophilus. When they colonize milk they convert the milk sugars into lactic acid lowering the pH of the milk. Most “bad” bacteria cannot grow in an acid (low pH) environment, so these little guys are protecting us by preventing nasty things from growing. Another benefit provided by our little friends, is that breaking down the milk sugars makes yogurt very easily digestible, even by people who are lactose intolerant. In fact, this is one of many reasons to make yogurt at home. Often commercial brands of yogurt contain added milk solids as a thickener which may not be tolerated if you have trouble digesting lactose. If you make yogurt at home, you can avoid this.
Yogurt making consists of four steps: scald your milk and then allow it to cool to 115F; add your yogurt starter; incubate your yogurt; and then refrigerate. Originally, the milk was probably scalded to kill the bad bacteria; these days we have pasteurization for that. However, you’ll notice that most yogurt recipes still have you heat the milk first. Why? The scalding process starts to unfold the milk proteins and when they refold during fermentation they form tighter bonds, resulting in a thicker, firmer finished product and less whey separation. You can make yogurt without heating your milk and in fact, proponents of raw milk do just that when they make raw milk yogurt.
In an attempt to simulate the original yogurt made in Central Asia eons ago, I used a very simple recipe containing just whole milk and a starter, nothing else. You can use any kind of milk you like and if you want a quick way to ensure very thick yogurt you can add powdered milk, which is essentially milk solids. As a starter, I used a few tablespoons of a commercial brand of whole milk yogurt that does not have any thickeners or stabilizers in it. Not all commercial yogurt is created equal, so read the label. You want to make sure your starter has active cultures in it. If it doesn’t say “contains active (or live) cultures” on the label then they’re not in there. You can also buy dried yogurt starter from a cheese making supply company.
Once you start making your own yogurt, you can do what our ancestors did and use a bit of your last batch to make the next one, just like with sourdough bread. If you choose to use the self-perpetuating method, the easiest way to ensure an uncontaminated starter is to make two containers of yogurt each time. One large one for the yogurt you will be eating and one small one (about 4 oz.) to create the starter for your next batch. That way the starter jar stays closed and uncontaminated until you use it to make your next batch.
Once you’ve blended the starter with the warm milk, pour the milk mixture into a sealable storage container and put it in a warm place to incubate. Ideally, the temperature needs to be around 110-115F (43-46C). But beware, you do not want the temperature to climb above 120F (48C), this will kill off our friendly little bugs. I have found success by putting my quart mason jar of yogurt in a cold gas oven with the interior light bulb left on. Other methods I have heard about include using a heating pad inside a container big enough to hold your yogurt jar, or a small enclosed space with a clip light and a 100 watt bulb. Experiment until you find a good incubation place in your home for yogurt.
How long to incubate is up to you, the longer you go, the thicker and tangier it gets. For medium thickness and flavor, try 6 hours of incubation. I like my yogurt thick so I leave it for 12-15 hours. When it has finished incubating to your satisfaction, put it in the refrigerator over night to stop the fermentation process and set the texture. If you like a super-thick Greek-style yogurt, you can strain the finished product through several layers of cheese cloth.
1 quart whole milk of the best quality, organic preferred
3-4 tablespoons whole milk plain yogurt with live active cultures, room temperature
1 quart sized container with a sealable lid
1 digital probe thermometer
Sterilize your jar and lid in a 225F (107C) oven for 5 minutes and then remove them and allow them to cool.
Over a medium-low burner, heat the milk to 180F (82C) and then take it off the heat and allow the temperature to drop to 115F (46C).
Mix the whole milk plain yogurt into the cooled milk. Be sure to whisk thoroughly; you want those friendly bacteria to be evenly mixed into the milk.
Pour the milk mixture into your sterilized 1 quart jar, leaving an inch or so of room at the top. Close tightly and place it in your cold oven with the lightbulb turned on inside or some other suitably warm place in your home (see above for suggestions). For mild flavor and medium thickness incubate for 6 hours, if you like your yogurt thicker and tangier you can leave it for 12-15 hours
When incubation is complete, move the yogurt to the refrigerator and chill for 24 hours. Serve plain or with fresh fruit and/or honey.