So you want to make your own yogurt? I said the same thing a couple years ago and have tried many different methods, milks, cultures, etc. The great thing about yogurt is that once you have a culture going, you can keep culturing multiple batches. It’s kind of like friendship bread in that way. The first method I tried was using a slow cooker to heat the milk to just under scalding, then letting it come back down to culturing temperature and culturing in the pot in an oven. It worked quite well, but never got extremely thick. If you don’t have an Instant Pot or yogurt maker, I would highly recommend this method.
Culturing needs to be done at 110°F, which is why an Instant Pot or yogurt maker will work best. I always sterilize all of my tools and yogurt containers before starting this. You can either use a dishwasher to sterilize or boiling water, whatever works best for you.
There are several different brands of yogurt culture available. I tend to use Belle + Bella, but Cultures for Health and any other non dairy yogurt can be used. If using non dairy yogurt, use somewhere 1/4 cup to 1/2 cup to start your culture.
I use either Westsoy Organic Unsweetened or Silk Unsweetened Soy Milk to make my yogurt, but try to use it upon first opening it. If you use it after it has already been open, there’s a chance that other bacteria can contaminate the batch and grow during the culturing.
You can also use homemade soy milk, if you want to go to that much effort. Other plant milks won’t thicken well because of the lack of protein, but the cornstarch can help them come close to the thickness of dairy yogurt.
If you don’t mind a little sweetness, you can add a little sugar which will help the yogurt culture quickly. You can also use a premade vanilla soymilk with added sugar if you want a sugary yogurt (it will still have less sugar than the store-bought kind.) The bacteria in yogurt use sugar as food, so the more sugar in the milk the quicker it will culture.
This yogurt can also me made without the cornstarch, but it won’t be as thick as pictured. I’ve found I prefer the texture of the thicker yogurt and straining with a cheesecloth has never helped me much.
If your cornstarch clumps on you, and immersion blender can be used in the pot to break up the clumps. Cornstarch does tend to cause a skin to form, so be sure to give it regular stirs in the pot to avoid this. I use a regular instant read thermometer to check the temperature, but if you miss the 108-112°F window, you can easily heat it up a bit to get it to the right temperature.