There are lots of sites where you can find blog posts, etc. about this, but I thought I'd document how I managed to do it in Korea. Yogurt only requires milk and bacteria, which can be easily borrowed from a package of existing yogurt. I taste-tested 5-6 different kinds of plain yogurt, organic and not organic.
WINNER: Denmark Plain Yogurt
It doesn't have a sweet taste from additional sugar that all the other yogurts had, and it has a nice, thick texture which I was hoping would transfer to my own batch of yogurt. It's also possible to use a yogurt starter to make your own yogurt, but I have no idea where one would get a hold of that in Korea. And why would you want to go search out something as obscure and difficult to find as yogurt starter when you can go to your local market and just buy some yogurt as starter?
Many blogs cannot emphasize enough that ultra-pasteurized milk is the worst thing you can use to make yogurt or cheese. Unfortunately, Korea absorbs technology well, and most milk you find in supermarkets is ultra-pasteurized. I went through all the cartons of milk at E-Mart in Yongsan and my local supermarket (Well-Being Mart in Gyeongnidan) and found a way to differentiate ultra-pasteurized milk from just pasteurized milk. Ultra-pasteurized milk is heated to 130°C while just pasteurized milk is heated to between 72-75°C. Every milk label shows this information so just scan the area above the nutritional information for numbers and a degrees symbol. Basically all Korean milk (Seoul Milk, Maeil Milk, Einstein, E-mart, etc.) is ultra-pasteurized. The only milk that isn't is Denmark Milk and Pasteur Milk. I've been using both. Pasteur Milk is a bit more expensive, but pasteurized at a lower temperature of 62-65°C. They have whole milk, low fat milk and skim milk. Denmark Milk is pasteurized at 72-75°C but only for the whole milk and low fat milk. The skimmed milk is ultra-pasteurized. For the purposes of making yogurt, I chose to go with Pasteur Milk's whole milk.
*Note: Since I've posted this, I've found that ultra-pasteurized milk DOES WORK. I just made a batch and am feasting shamelessly on it now. This is great news since ultra-pasteurized milk is much cheaper and easier to get.
To make yogurt in a slow cooker, you'll need the following:
- 1/2 cup yogurt with live active cultures (an 85g container of Denmark Plain Yogurt)
- 1/2 gallon milk (about 1.8 Liters) not ultra-pasteurized milk (Denmark or Pasteur Milk; start with whole milk and when you feel comfortable move onto low fat milk)
- slow cooker/crock pot
- wire whisk
- thermometer (I use a candy thermometer which goes up to 100°C that I bought at the bakery market in Bangsan Market near Euljiro/Jongno-3-ga for 3,500 won. You can also buy them online at the baking school.)
- thick beach towel or blanket
Next, turn the slow cooker off and with the lid on, let it sit and cool down to 110°F (43°C). If you skip this step or don't wait long enough for it to reach the right temperature, when you put in your yogurt, it will be too hot for the yogurt. This should take 2-4 hours so go find something to do.
When it reaches 110°F (43°C), the milk may have formed a skin at this point; I would skim that off. Take out a cup of the warm milk and whisk in the 85g container (1/2 cup) of yogurt. Then whisk the milk/yogurt mixture into the milk into the slow cooker, and whisk well so that the cultures can colonize and make your yogurt. Then put the lid on and cover the slow cooker in a blanket or heavy beach towel and let it sit for 8-12 hours.
Then you should have yogurt!
Refrigerate it for 8 hours so that it can "set" and have a better consistency. You can eat it right away but it'll be warm and gross. Wait, and you'll get something as amazing and wonderful as THIS:
You can strain it in cheesecloth to get a thicker consistency like Greek yogurt. I don't bother because it's already pretty thick, and I've already waited 8 hours. Also, I like to add fruit to mine. These are strawberries from Costco all chopped up.
1.8 Liter of milk = 5,000 won
1.8 Liter of Denmark Yogurt = 9,000 won approx.
Since 1.8 liters of milk yields 1.8 liters of yogurt, making your own yogurt at home costs about 45% less than buying your own yogurt, and if you time it right, it doesn't really interfere with what you'd normally be doing anyway (Facebook).
*Since I've discovered that you can use ultra-pasteurized milk for this, you save even more.