A quart sized container of organic, whole milk yogurt costs about $4.29 at most stores around here in Minnesota.
A quart of home made, organic, whole milk yogurt costs me $1.60 and takes a total of 5 minutes of my time to make.
You need a crock pot, 3 quart sized jars with lids, just under 3 quarts of whole milk, a few tablespoons of plain whole milk yogurt, an instant read thermometer, and a stock pot.
So you dump just under 3 quarts of whole milk into your stock pot. Set on the stove and heat to almost a simmer (little bubbles will form at the sides). Turn off the heat, and let it cool back down to skin temp (use your finger).
Put a few tablespoons plain, whole milk yogurt into a medium bowl. Stir a few cups of the warm milk into the yogurt, then pour it all back into the stock pot, stirring well.
Pour the mixture into the quart jars, leaving a bit of room at the top. Lay the tops on the jars, but do not tighten. I have the white plastic ones in the picture above, but a regular canning lid works great. Skip the ring for now, just set the lid on the jar.
Fill your crockpot (oval shape is swell for this) and fill with a couple inches of water. Set the jars in the water and turn on your crockpot to WARM, which is the ideal setting. If you don't have warm, use LOW, but make sure the water (and the yogurt) never go above about 115 or 120.
The rest is up to you. I like mine to "cook" for at least 8 hours. It can go 10, 12, or more! The longer it goes, the thicker and tangier it gets. You can use your instant read thermometer to check the temp of the yogurt and the water. I trust my warm setting, so I'll often start my yogurt before bed, and by morning it's ready to hit the fridge.
To serve, you can add sweet (honey, sugar, maple syrup), vanilla, fruit, whatever you like. NEVER add anything to the yogurt while it cooks. Thank you!
If you like thick "Greek" style yogurt, here's a nifty trick. Chill your finished product. Then, in a clean flour sack towel or several layers of cheese cloth set over a large bowl and in a strainer, dump your yogurt. Let the liquid (the whey) drain off and after 30-60 minutes you'll have a lovely, thicker product. Let it go even longer and you'll have "yogurt cheese" which can be doctored up with herbs and tasty things and used as a spread, or like ricotta cheese, or any number of other things. SAVE THE LIQUID that drains off. It's called WHEY and it's full of yummy good happy live bacteria. Use it for soaking oats, or soaking other grains, or add to soup or smoothies.
That's yogurt. Five minutes of work for a home made product that costs $1.60 vs. $4.29.