Homemade Greek Yogurt in a Crockpot: How I Did It and What Not to Do

In case you are not among the hapless schmucks who follow my self-indulgent documentation on Facebook, my most recent domestic experiment consisted of an appropriately seasonal diplomatic mission with the colonies -- bacteria colonies, that is. I was determined that Greek yogurt, one of my four basic food groups amongst coffee, kale and snark, should absolutely be something I learn how to make on my own, and I'm pleased to report that I succeeded. 

Initially, I considered investing in a yogurt maker, but that somehow felt like A) cheating and B) a waste of precious counter/cabinet space. Instead, I followed The Tasty Cheapskate's recipe for crockpot Greek yogurt "for dummies." Since either I'm a special breed of dummy or the recipe isn't quite as dummy-proof as I'd hoped, I'm going to share my process as well as what absolutely not to do. As a disclaimer, I have attempted this a total of twice, once with success and once with a mild case of food poisoning. Since they didn't occur in that order, I'd say progress was made.

Rule #1 of yogurt making/biggest mistake I made the first time since it wasn't mentioned in the recipe: KEEP EVERYTHING SCRUPULOUSLY CLEAN. Any bad bacteria you introduce or don't eliminate has the perfect environment to propagate itself and wreak havoc on your digestive tract. Anything that comes into contact with the yogurt should be sterilized, including spoons, thermometers, jars and the crockpot itself. I kept water boiling in my electric kettle throughout the yogurt-making process and poured it over any new utensil to be used -- I suspect you could also sanitize everything all at once, if you're better at planning than I am.

Rudy is why we can't have nice things.

To get started, you will need a 7-quart crockpot, a reliable thermometer, an oven or other draft-free warm environment, a thick sacrificial towel, a gallon of whole or 2% milk (I used whole and can't vouch for 2%), 1/2 cup of plain yogurt* for starter, enough airtight containers to hold a gallon collectively, and a large chunk of time to devote to babysitting your batch. I suggest starting on a weekend afternoon about six hours before you usually go to bed, on a day when you have nowhere to be in the morning. Supervision's only really necessary when the milk is coming to temperature, but I wouldn't leave it alone until its temperature is stable.

*When selecting a yogurt for a starter, the most important thing is that it have the five requisite live cultures and minimal extra stuff like pectin, flavoring, gelatin, etc. -- you can determine all of this by checking the tub it comes in. Look for a good plain yogurt whose flavor and consistency you like -- I used Mountain High. Greek yogurt starter does not make Greek yogurt; in fact, using Greek yogurt as a starter can throw off the bacteria balance and give you a wonky batch.

Now, then. On to the process:

1. About six hours before you want to go to bed, pour your gallon of milk into your sanitized crockpot, put the lid on, and turn it on Low. At this point, you should be able to leave it alone for two hours or so. Take the milk's temperature periodically to see how fast your crockpot heats up -- I generally crank mine up to High after two or three hours when I get impatient. The idea is to slowly heat the milk to 180 degrees to kill any harmful bacteria present in the milk.
2. When the milk reaches 180 degrees F, turn the crockpot off, unplug it, take the lid off, and leave it to cool to about 130 degrees. This takes about an hour, so don't stray too far. The milk will develop a skin throughout this process -- just skim it off with your thermometer and flick into the trash. Do not stir it in, or you'll have gross slimy lumps in your yogurt. Do NOT rinse your skimming implement in tap water and put it back in the yogurt, or you might as well pitch the whole thing now.
3. When the milk reaches 130-ish, get your starter and your oven ready. I like to measure my yogurt into a Pyrex measuring cup -- you'll want something roomy that you can pour from, and make sure it's sanitized! Arrange your oven racks to the lowest level, and make sure your oven is warm but not hot. I turned my oven on to Warm for a bit, but some people just turn the oven light on or set the oven to a bread proofing temperature (spoiled bastards). A too-cold oven will slow down the culturing process, and a too-warm one can kill your bacteria.
4. When the milk reaches 115 to 110 degrees, ladle a bit of milk into the measuring cup with the yogurt, and whisk them until they're smooth. This tempers the yogurt and keeps you from having lumps. Mix this slurry back into the crockpot of milk, working quickly so your temperature doesn't drop below 110.
5. Put the lid back on the crockpot, and wrap the the whole thing in your sacrificial towel. Stick the bundled-up crockpot in your warm but NOT HOT oven (you want it to maintain around 110 degrees overnight), and close the door. Leave the oven light on if you can. If you have a self-cleaning oven with one of those little levers that locks the door, use this to help trap heat. If you share your oven with others, leave a note so that no ones turns it on. Once your crockpot is all tucked in, you can hit the hay. 

Soft yogurt, warm yogurt. . .

In the morning/after 8-ish hours, check your yogurt. It should be set up, like gelatin. If it is still runny but looks yogurty, you can stick in back in the oven to continue curing longer. You can also let it cure longer if you like a tangier yogurt, so be sure to test. DO NOT try to heat it back up -- this was a giant mistake I made the first time. Also, do not stir it at this stage, or you'll end up with a nasty cottage cheese consistency. If you're happy with flavor and consistency, take half a cup off the top right away, and stick this in the freezer to start your next batch. Then, you can go ahead and scoop the yogurt into your choice of airtight containers and stick it in the fridge.

If you like a good thick Greek yogurt, you can strain off the whey (make sure to take your starter for next time before straining so the bacteria balance is correct). Set up a large colander over the sink (if you don't want to keep the whey) or over a large container (if you want to keep the whey). If the latter, make your colander a little kickstand of some sort so the colander doesn't sit in the whey as it accumulates. Line your colander with a clean tea towel, T-shirt or cheese cloth, and pour/scoop in all your yogurt. Leave this for two to six hours; the longer it sits, the thicker your finished product. I left mine for a little over two hours as I had somewhere to be, and the finished product was about Yoplait consistency. In the future, I'd leave it a couple hours longer.

Turn and face the strain . . .

When your yogurt has strained to your desired consistency, you can either pack it up right away or whip it with a mixer or eggbeater to ensure a uniform texture. Once your yogurt is packed in its airtight containers, it purportedly lasts in the fridge up to two weeks. If you don't think you will go through it that quickly, you can freeze it (probably). If you chose to save the whey, use it in smoothies for a splash of protein, or use it as a buttermilk substitute in baking.

The total cost of the ingredients was ~$6 for a gallon of organic milk and half a cup of yogurt, which came out to about $0.50 per one-cup serving of yogurt seeing as I yielded three quarts. If I strained it longer, I'd probably yield 2-2.5 quarts at $2.50-$3 each, or $0.60, $0.75 a serving. Considering organic Greek yogurt retails for ~$3 a pint, that's a hell of a savings. If you reuse your containers and make a new starter every time, you can make this process even more economical.

Pro tip: before you wash all your dishes, slather some of that yogurt on your face. The lactic acid and beneficial bacteria make an excellent mask -- just rinse it off after ten minutes.