No, this isn’t gorgeous, creamy ice cream; it is actually homemade Greek yogurt. (Yes, I am a food geek.) After making the yogurt, I drain off the whey, reducing the total yield by half to yield all that creamy goodness. And then, we use that whey to make the next batch of yogurt.
But before we get into all that, I should dive into how I got here. Back in 2015, Mark and I were on temporary relocation in Sydney, Australia. While we were there, we discovered that yogurt was unexpectedly popular. Every breakfast buffet seemed to offer yogurt and muesli. At some point, I decided it was time to solve the mystery of making thick, tangy yogurt at home. Soon my tiny condo kitchen turned into a science lab. After a ton of experimentation, I figured out what works.
Get the Culture
Get some fresh, plain, whole-fat yogurt from the store. Look for one with active bacterial strains of Lactobacillus bulgaricus and Streptococcus thermophilus. Why both? Because they are what makes yogurt “yogurt,” and they help each other thrive.
Sterilize and Denature
Gently heat a half-gallon of whole milk to 185°F in a covered microwave dish or a stovetop bain-marie (hot water bath). The slow heating denatures the lactoglobulin milk protein. Forget about leaning on commercial pasteurization. It is too quick and intense to be effective. How do I know this? Because I brought five batches of whole milk to a range of temperatures (110°F, 145°F, 160°F, 170°F, 185°F) to test the theory. Only the batch that got to 185°F got nice and thick. See the difference?
Inoculate and Incubate
Pour that hot milk into 1-pint containers, cap, and set at room temperature to slowly cool to 110°F (a safe temperature for introducing the desired cultures). For each pint, measure out 3 tablespoons of that plain yogurt you bought earlier; gently stir to distribute the culture. Cap tightly and place the pint containers on a tray and incubate undisturbed at 110°F (an oven with just a light on works well) 8-10 hours. As the beneficial bacteria (probiotics) settle into their warm, comfortable space, they gobble up lactose and release lactic acid, lowering the pH. As acidity increases, the environment becomes unfriendly to potential pathogenic bacteria. Meanwhile, the acidity denatures casein (another milk protein), which promotes thickening.
Refrigerate then Strain for Greek Yogurt
Chill the pints 24 hours to help the yogurt structure set. After chilling, it’s time to convert it to Greek yogurt. I learned this trick after we got back to Charlotte. Just spoon the yogurt into a lined colander set over a big bowl. For the liner, a paper towel or a lint-free synthetic cloth works very well. Place a saucer with a bowl over the top to strain off the excess whey. After straining, pour a cup of the whey into a jar, cap, and refrigerate. Now you can use the whey (instead of yogurt) to make the next batch. I tested to make sure it works, running a three-way experiment with yogurt, whey, and salted whey used as inoculators. Success! Make the next batch of yogurt at around day 7 when the probiotics are most vigorous.
There you have it. Making yogurt is easy once you know what you are doing. Essentially we use TEMPERATURE and TIME to eliminate initial pathogens and to denature lactoglobulin. We introduce desirable CULTURE, which lowers pH, protecting against potential pathogens and denaturing casein. Ultimately, temperature, time, and culture work together to deliver the texture and tang we expect in yogurt. Making Greek yogurt is just one more step to get to that creamy goodness that we love so much.