A word before we get started… I want to encourage you that making yogurt is probably much easier than you think! You might think that they wouldn’t sell it at the store if it was easy to make, but that’s not true. Sure, buying yogurt is easier and faster, but do me a favor and try this procedure just once to see how easy it actually can be. I thought of calling this Instructable 'No-fail Yogurt' but hey, sometimes this stuff fails.

If you follow this procedure, it is highly unlikely that you will create anything that is unhealthy for you. Milk has a handy way of turning really disgusting and unappetizing if it has actually gone bad. But keep in mind that yogurt, cheese, kefir and a number of other dairy products are simply milk gone bad in very particular ways under controlled circumstances. The idea is to control what grows in your milk so that it is only the good stuff that develops the flavors and textures that you want. However… if you do something stupid and drink that hairy, green, smelly stuff after you left your ‘yogurt’ out for a few days, don’t blame me. If it’s gross and doesn’t look right, chuck it.

Now let's get started!

Step 1: Gather Tools & Ingredients

Thermometers- You must have a thermometer for this to work correctly, that is, until you get a really good sense of the temperatures involved. But don’t try it for the first time without a thermometer! I like to use two since you will be measuring the temperature of the milk and of some water, but you definitely don’t need two. I also prefer to use a regular thermometer (usually my deep fry thermometer) that I can leave in the milk as it cools, and an instant read for all the other uses.

Mason Jars – I suggest using smaller jars, probably no larger than a pint. You can use very small jars that are 8 oz or smaller and consider them serving sizes, but I’ve found that to be kind of a pain. I prefer wide mouth pint sized jars. Lids – You can use regular two part canning lids if you want, but I got the wide mouth plastic lids because they don’t rust after having been exposed to water, and they are super handy when using mason jars for storing things or for other kinds of projects.

Cooler – You can use whatever kind of drink cooler that you have around your house. You could even use a Styrofoam cooler, but it would get beat up kind of quickly if used regularly. My suggestion here is to fiddle with the number of mason jars and the coolers that you have available, and try to find a kind of snug fit for the number of jars that you want in each batch. I prefer to have a bit of room around each jar rather than jamming them together, and you do want some room around the jars for water. My favorite for this project is a cooler made for a six pack of long neck bottles that has a nice carry handle and just enough room for about 4 pint jars with space for water. Play with it and find something that works.

Funnel (optional)- I like having a stainless steel canning funnel when I am filling the jars since I make a horrible mess when trying to pour the hot milk from a pot into the jars. If you don’t have one of these, don’t go get it, but maybe you should scoop your milk out of the pot with a measuring cup and pour into the jars that way.

Milk - Use your preferred milk, but you’ll find that lower fat versions might work best. You can definitely make yogurt out of all kinds of milks, including goat’s milk and other things, but don’t start there. Even if you’ve got a goat and a cow right there in your kitchen, I suggest using store bought milk a couple of times to get the procedure down before you complicate things. I also suggest that you make your yogurt from a fresh container of milk, not one that has been open for a few days. You never know what that milk has been exposed to while sitting around. It likely wouldn’t affect the outcome since you are going to pasteurize the milk again, but I really want this to work for you the first time, so let’s eliminate as many risks as possible okay?

Yogurt - You need a yogurt with ‘live and active cultures’ that you’ve bought from the store or from a previous homemade batch. I suggest buying the smallest container of ‘plain’ yogurt that you can find at the store. You might even want to consider getting organic yogurt even if you aren’t using organic milk. It will work either way, but you might get a better culture out of the organic versions.

Add-ins – I suggest that you don’t try to make yogurt with flavors and sweeteners, especially for your first few times around. People really differ on this as a whole, but I think you’ll have the best results if you always make plain yogurt and do your additions on a per-serving basis after your yogurt is complete. To make fruit flavors, add a couple of tablespoons of jam and stir it in. If you don’t like tart yogurt, stir in a sweetener such as honey or stevia to each serving. This gives you the most flexibility and the best chance that your yogurt will always turn out right and you won’t waste batches that don’t ‘yogh.’

Step 2: Set Up

Start this process in the evening, after dinner and before bed. The 8 hours you are sleeping is about the right amount of time to for the yogurt to ‘yogh,’ or solidify.

Check to see that your jars fit in the vessel you are using for the fermentation step (your 'cooler').
Run your mason jars, funnel and lids through the dishwasher immediately before you start this project. Don’t hand wash them, we’re doing this for the heat cycle in the dishwasher. There are lots of ways to sanitize your jars, but remember, I’m trying to show you the easiest and most successful way first!
Measure out the right amount of milk to fill the number of mason jars you are using in this batch.

Step 3: Pasteurize/heat the Milk

Put the milk in the pot and heat until just before the milk starts to boil (Over 145 degrees). If you scald the milk and a skin forms, scoop the skin off with a spoon.
Turn off the heat and let the milk cool to 115 F.
Meanwhile, pour about two inches of water into your cooler and then dump that water into a pot on the stove. Heat the water to 115 degrees or so. You should still be able to stick a finger in the water without it hurting

Step 4: Make the Yogurt

Open the new container of store bought yogurt and scoop one big heaping spoonful out and stir it into the milk really well. Don’t just dump the lump in the pot and expect this to work!
Distribute the inoculated (sounds gross, but it isn’t) milk into your jars and put the lids on right away.
Put the jars in the cooler.
Pour enough of your warm water into the cooler so that it comes most of the way up the sides of the jars, but don’t cover the jars. The jars are probably sealed by the lids, but there’s no reason to take risks of leakage.
Close the lid on the cooler.
Carefully move the cooler to a warm-ish location where it won’t be jostled or moved until morning. Be sure you don’t set it in a draft or put it somewhere the kids will kick it. Sometimes yogurt fails to solidify because it gets banged around too much. Be gentle!
Cover or wrap the cooler in blankets.
Go to bed.
Get up in the morning and put your nice new yogurt in the fridge until it cools. Enjoy!