1) Pour a gallon of milk into a Crockpot (I used 3 quarts as I was saving a bit to make cheese).
2) Turn the Crockpot on High and raise the temperature to 188 F (this took about 4 hours).
3) Cool the milk to 112 F (this took about 1 hour. I opened the lid to cool the milk faster).
4) Put your culture in the milk. Cover with a lid and towel.
5) Let sit approximately 12 hours. I let mine sit overnight. The temperature dropped a bit so I turned the Crockpot on low for a bit in the morning to raise the temperature.
6) At this point you have yogurt. I have turned the Crockpot a bit so you can see the edge of the cake and the whey:
7) Greek yogurt is so much thicker because it is strained. Cheesecloth in a colander (on a pan to catch the whey, of course!):
8) Let it drain. Here are two pictures, one early in the process and one about an hour later:
9) When it is firm, scoop it out into a container. You can add flavorings (syrups or fruit) at this point. I just like mine plain:
10) A by-product is whey, the milk and solids (proteins) in the milk. People pay ridiculous amounts of money for dried whey. I got four cups:
So how did I do? House Greek Yogurt (905 g) in my neck of the woods starts at $3.78, with prices going up to $6.00 for the brand name flavored varieties. I got 996+ g (our scale maxes out at 1000 g) from 3 quarts of milk. A gallon of milk cost $2.48. My yogurt culture packs cost $6.95 for 5 packs, so approximately $2.80 for two (from the super friendly folks at New England Cheesemaking Supply Company). That brings us to around $5.20.
But wait, there is more. I used the last quart of milk to make a soft cheese. Add a minimum of $5.00 for that. And I ended up with 8 cups of whey between the yogurt and the cheese. 907 g of powdered flavored whey will run $22.00 at a store. Mine I got for free as a byproduct of something I will eat.
So cost-wise I am ahead (yes, I could go higher with organic milk but I bet I would break even with higher priced yogurts).
More importantly, I have a skill that (in an urban area) is handy to have. I do not have a ready supply of milk except from the store - but right up to that point, I can transform milk into different products and products with longer lives (Hard cheese ages for example, and waxing cheese can help it keep for years). Right up to the point of a collapse, even if things become rationed, I can make something more out of what I have available.
And what is the value of that?