You will need a gallon of milk in a plastic jug, a pot bigger than that jug, 2 coffee filters, 2 oz. of plain yogurt in a cup-sized jar, a pair of gallon-sized shallow food containers, an insulated container to hold the jug, a drill or sharp knife, a cooking thermometer, and a kitchen with a stove, fridge, and sink.
The cheat sheet.
1. Sanitize everything.
2. Heat to 180 - 190F.
3. Cool to 100 - 110F.
5. Ferment for 6 - 24 hours.
6. Strain in refrigerator.
Step 1: Scald the Milk to 180º - 190º
It takes my electric stove about 25 minutes to heat the milk to 175F. Then turn off the heat and let it coast up to 180+. I use a timer so I can turn my attention to other things, but depend on the thermometer.
It's hard to find the perfect vessel for this, but it really doesn't matter to the yogurt. Mine is a 12 quart aluminum pot, over 10 inches high inside, with a glass lid that has a vent hole. It saves time and heat. You can do this in an open 3 quart pot for a trial run, but it's more trouble.
Step 2: Cool the Milk to 100º - 110º.
Cooling time depends on the temperature of your tap water and kitchen air. Plan on a half hour in water to reach 110F, but depend on your thermometer. At 112F, dry off the jug and prepare to inoculate. But the exact temperature doesn't matter that much to the yogurt.
Step 3: Inoculate
Step 4: Ferment
You can use a cooler with foam peanuts or bubble wrap or whatever. Just don't use towels or they will smell a lot like yogurt. Which isn't as delightful as you might think. There is no need for a heater or worries about electrical failure. If your home is cold, build a nice thick foam box and preheat it with hot water.
I usually let the batch ferment overnight. Sometimes 6 hours if I'm in a hurry. Sometimes I forgot it for a whole day. The yogurt doesn't care.
Step 5: Strain the Yogurt
I like thick yogurt, so I developed this strainer. It is made from a pair of gallon-sized food containers. Since they nest, only 1 cover is needed. I drilled about 50 1/8th inch holes in the bottom of the top container. You could do just as well by gouging out a dozen rough holes with a knife. The yogurt doesn't care.
I cover the holes with 2 coffee filters. The top container is set into the bottom container. Then I pour in the yogurt. But not quite all of it.
I put the lid on and leave the strainer on the counter for an hour or so to drain. Why shock my fridge when I can just pour off warm whey?
The strainer is showing no signs of wear from 16 months of constant use.
Step 6: Store and Serve
But there is one thing: I want to save some of each batch to inoculate the next. So the last few ounces out of the jug go into a jar. I leave this starter untouched for the week in the fridge.
Step 7: But Wait … There's More!
Step 8: The Circle of Life
This is a robust process. Over the past 2 years I have fermented about 80 gallons of yogurt. I've used different gear and different milk and made every mistake. For the past 60 batches, I have used only my own starter. Still *never* a failure. I am careful about sanitation; brush cleaning everything with a little bleach in my dish detergent. But my kitchen isn't a laboratory. This bacteria is so territorial, it's fighting off other microorganisms. It creates it's own environment for its safety and our delight. After 60 generations, it's growing like fresh culture.
I tried some batches with added dry milk. That's just more trouble and expense. Fluid milk is cheaper than the equivalent powdered milk. If I need more yogurt for a special culinary project, I'll buy a 2nd jug.
After losing a lot of weight and radically improving my health, I have switched from skim to whole milk. The resulting yogurt product is luscious. Like cream cheese (but with flavor), you can spread it on toast. Of course I use it for fruit smoothies every morning. With a dab of olive oil and spices, it makes wonderfully thick and creamy salad dressings. When loaded with Southwest spices or wasabi, it sauces sandwich meat. Creamy belly-filling vegetable soups too.
With foamed cream or pasteurized egg white, it makes a sweet whipped pie filling. Oh yes. I hope to spend years discovering new yogurt desserts. And living well.
Cheers from Sarasota.