I've Become a Homemade Yogurt Machine

Yogurt has been the latest frontier in my dairy kitchen. Let my first yogurt attempt be a lesson for us on what being a corner-cutting, lazy pile will get you. What should have been the most simple of my first four attempted cheese recipes went straight into the garbage on the first batch. There's not much to making yogurt. Just four basic steps: heat the milk, cool the milk, inoculate, and incubate.

A successful batch on my second attempt

You heat your milk to allow the protein to break down to the point where the yogurt cultures can do their work. This is called denaturing the protein, which occurs once the milk reaches 180-185 degrees Fahrenheit. As the milk heats on a high burner setting, continue to stir so it doesn't scorch. As soon as you hit the temperature, you immediately start to cool the milk to 110-115 degrees Fahrenheit. Usually I accomplish this step by taking the 180-degree pot and setting it in an ice bath I've prepared in my sink. 

Now, inoculate! Once the milk has cooled, add the starter cultures. You could buy a packet of direct set cultures and add it to the pot as you would with any other cheese recipe. Cheaper yet, because finished yogurt is full of live and active bacteria cultures (that is, after all, often its selling point, see Activia commercials), it can act as its own starter. So simply adding existing yogurt to the milk would work as well. The cultures in the old yogurt will start eating the lactose in the milk to create a new batch. Yogurt cannibalism, if you will.

(Note: many store-bought yogurt brands have killed off the live cultures by heating after incubation to improve shelf-life or control flavor. Yogurt without live/active cultures do not contain any active bacteria that will incubate a new batch, and therefore will not work. Make sure you read the labels.).

The appropriate ratio is usually two to four tablespoons of existing yogurt per half gallon of milk in your pot. The correct amount may vary depending on the acidity and active culture levels in your existing yogurt. You may need to experiment if your first attempt doesn't set. Also, as you continue to make new batches with the previous generation of yogurt, the bacteria may become less active. Generally after eight or so successive batches, the yogurt-on-yogurt starter culture method stops working. At that point, you'll need to start over with a direct set culture packet or buy some fresh live culture yogurt from the store to start the culture strain over. 

Stir the cultures into the milk, and let it incubate around 100-115 degrees Fahrenheit for anywhere between 5 to 12 hours. You probably won't start to see the milk setting until at least four hours after adding starter. For this step, I set the pot in a double boiler on the stove at the lowest burner setting for a few hours while the temperature levels out. Then just before going to bed, I turn the burner off. The yogurt will hover near the incubation temperature for a while and cool overnight.

The overnight incubation gives me a slightly thicker yogurt. Also, if most of you out there are normal people with a job who start most of your cooking in the evening, you'll likely need to let it incubate overnight versus sitting up with your incubating yogurt baby. 

On my first try, I successfully achieved the denaturing and cooling step. Then, things got ugly. I knew a double boiler system would likely be the best way to control the temperature. Some people use a fancy thermos-type contraption called a Yogotherm to stabilize the temperature. If you're not using more than two quarts of milk at a time, this would work for you. If you're making big batches, or like me are just too cheap to spend forty bucks, then a double boiler system will work just fine. It only requires a couple more trips to the stove to monitor your thermometer. As you might imagine, just leaving the pot on the stove without a double boiler and  without checking the temperature is not a good way to go. Emptying soup from my larger pot into tupperware, cleaning it out, and using it as a double boiler seemed like too much effort. So I skipped that step. Unfortunately even the lowest setting on my burner turned my pot of milk into a really gross creme brulee. It was stupid and lazy on my part. But I learned and kept trying. 

Double boiler. I learned my lesson.

My second attempt was a success. I used a double boiler, kept it around 105-110 for four hours, turned the burner off and let it set more overnight. On my successive attempts, I used 2% milk. We eat a lot of yogurt, and I need to save some daily fat allotment for all the ice cream, cheese, and steak. I wasn't sure if the low fat milk would set, but it worked just fine. The yield was lower and the finished product was runnier. I like thicker yogurt so I simply drained the yogurt for a couple hours in a cheese cloth (a finely knit strainer over a bowl would work too). Draining the yogurt also smooths out the texture and flavor. Adding dry milk powder or cream, I'm told, will also thicken your final product. After draining, the 2% milk made an equally creamy and rich, but healthier, yogurt. I suppose skim milk would work too with some draining...but why? Unless I develop a heart condition, I'd like to keep my milky-water experiences to a minimum...like when I'm drinking tap water in Flint, Michigan. 

If a film develops after incubation,
simply skim it off before transferring
to a storage container.

Different recipes will give you different temperature ranges for each step. Generally they are all within 5 to 10 degrees of the ranges I use. Other than the temperature needed to denature the protein, which really does need to be at least 180, the other steps will simply affect the texture and flavor of the yogurt. If you incubate at higher temperatures, the yogurt will get thicker and tangier. Lower temperatures will give you a runnier yogurt with less tang. A longer incubation time will also create a tangier yogurt. Instead of leaving the yogurt out overnight, you could put it in the fridge as soon as it sets to cut incubation time (generally around the four to five-hour mark).  

After my initial failure, I've made four new batches of yogurt. Sure it takes some time for a finished product, but making your own yogurt at home is cheaper than buying the same amount in the store. Plus you get some Oregon Trail-style street cred. It's about as old-timey sounding as churning your own butter.