Yogurt is one of the first fermented foods I learned to make, and it is in constant rotation in our home. Our toddler loves it with strawberry jam, and it's also delicious with granola and fruit for breakfast, or added to a smoothie. Along with being an excellent source of protein and calcium, yogurt also contains probiotics, which are wonderful for digestive health.
Much like sourdough bread, in order to make your own yogurt, you must first make a starter batch, which will then be used for making the subsequent batches. As long as you continue making a new batch of yogurt every week or two, all you need is milk and a bit of the previous batch of yogurt.
There are two methods for making a starter batch. The first is to purchase a starter culture. The second is to use store-bought yogurt as your starter. I do the same process for both methods, although if you are using a starter culture, you'll want to check the instructions in case it requires a different process to activate. I have tried both methods, and have had mixed results with both, so just know it may require some trial and error before you get a good starter going. Once you have a good starter though, it should be no problem to make delicious yogurt every time!
Troubleshooting for your starter batch --
With using a starter culture, I found the issue was either an expired culture, or I did not let the starter ferment long enough. Fermenting for at least 12 hours usually yields a thicker, smoother yogurt.
With store bought yogurt, I had to try a few different brands before I found one that successfully fermented the milk. I believe this is due to some store-bought yogurts not having live probiotics in them. The brand that I found to yield a good starter was the Brown Cow Whole Milk Yogurt. No matter which brand you use, always make sure to use Plain, Whole Milk yogurt (no flavorings!).
Here is how to make your starter in the slow cooker:
Pour 1/2 gallon whole milk in the slow cooker. Cover and set on Low for 2 1/2 hours.
After 2 1/2 hours on Low, turn off the slow cooker and let sit for 3 hours.
Stir in your starter culture or or 1 cup of store bought yogurt, cover and wrap the slow cooker in a thick towel. Let ferment for at least 12 hours.
Check after 12 hours - if it's not thick enough, you can continue to let it ferment for up to 24 hours.
Once the yogurt is to your liking, transfer it to jars and refrigerate.
To continue making yogurt, simply use 1 cup of your starter or previous batch of yogurt, for every 1/2 gallon of milk used, and follow the same process outlined above. I like to start it around noon, and then transfer to jars the next day, also around noon.
Once you have a good starter and get the hang of it with the method, making your own yogurt is so easy and a great way to add fermented foods to your diet. It is also much less expensive. With current prices, our homemade yogurt costs about $1 per quart, verses $5 per quart at the store!