Yogurt

Yogurt contains Lactobacillus acidophilus (嗜酸性乳酸菌), Bifidus (比菲德氏菌，雙叉桿菌), and many other good bacteria. Maybe we will try to do it. But without proper way to maintain ~43 oC, we have to think about how to do it. We tried to use our rice cooker and found its maintenance temperature is too high. Maybe it is because this is a new one because it worked fine when we used our old one in US.

By the way, I saw some articles said that it is better not to use commercial yogurt to make your own yogurt even it said there is "active culture" inside the yogurt. They suggest to use commercial "dry yogurt culture" to grow active culture every time.

---- References ----
優酪乳發酵機 (ps. there are some useful information in here including what are those bacteria in yogurt, the nutrients composition in yogurt, and how to make it)

dave 2007: 自己做yogurt (ps. based on the wikihow "How to Make Yogurt")

Yogurt (ps. another person's experience)

How to Make Yogurt
Sure, it's easy to stroll down the supermarket aisle and throw a cup of yogurt into your cart; but have you ever been tempted to make yogurt yourself? Here's how to craft your own brand of yogurt in the comfort of your kitchen.

Ingredients

* 1 quart milk (any kind)
* 1/4 to 1/2 cup non-fat dry milk (optional)
* 2 tablespoons existing yogurt with live cultures (or you can use freeze-dried bacteria instead)

Steps

1. Sterilize the milk. Even though your milk has been pasteurized, it will still contain bacteria. Pour a quart of milk into a pot or the top of a double boiler. Use a metal spoon for stirring. Heat the milk until it is almost boiling. You'll see small bubbles form around the edges and steam beginning to rise. Keep checking the temperature: It should be around 180-185F (82-85C). A candy thermometer comes in handy. Heat slowly and stir often to prevent scorching.
2. Cool the milk to grow the yogurt. Allow the milk to cool at room temperature or in the refrigerator. Stir frequently to make temperature checks more accurate. Don't proceed until the milk is below 120F(49C), and don't allow it to go below 90F (32C). 105-110 (41-43) is optimal.
3. Warm the starter. Let the starter yogurt sit at room temperature while you are waiting for the milk to cool. This will prevent it from being too cold when you add it in.
4. Add nonfat dry milk, if desired. Adding about 1/4cup to 1/2 cup nonfat dry milk at this time will increase the nutritional content of the yogurt. The yogurt will also thicken more easily. This is especially helpful if you are using nonfat milk.
5. Add the starter. Add 2 tablespoons of existing yogurt, or add the freeze-dried bacteria.
6. Put the mixture in containers. Pour your milk into a clean container or containers. Cover each one tightly with a lid or plastic wrap.
7. Allow the yogurt bacteria to incubate. Keep the yogurt warm to encourage bacteria growth. Between 105F and 122F (41C and 49C) is ideal. An oven with pilot light is one option; see Tips for others. Use your candy thermometer to check on the temperature. Wait until the yogurt is thick, about the consistency of pudding. Keep the yogurt still during this process. It can take anywhere from 8-14 hours to incubate.
8. Refrigerate the yogurt. Place the yogurt in your fridge for several hours before serving. It will keep for 1-2 weeks. If you are going to use some of it as starter, use it within 5-7 days, so that the bacteria still have growing power. Whey, a thin yellow liquid, will form on the top. You can pour it off or stir it in before eating your yogurt.
9. Add optional flavorings. Experiment until you develop a flavor that your taste buds fancy.
10. Use yogurt from this batch as starter for the next batch.


Tips

* Your first batch is always the hardest.
* You can use any kind of milk, including whole milk, 2%, 1%, nonfat, pasteurized, homogenized, organic, raw, diluted evaporated, dry powdered, cow, goat, soybean, and more.
* All yogurt needs "good" bacteria. The easiest way to add this is to use existing yogurt. The first time you make your own yogurt, use store-bought plain yogurt. Be certain it has "active cultures" on the label.
* Alternatively, instead of existing yogurt you can use freeze-dried bacteria cultures (available in specialty stores), which are more reliable as a starter.
* Using a double boiler makes it easier to control the temperature.
* If your oven doesn't have a pilot light but does have an oven light, preheating the oven to the desired temperature, turning it off, and then leaving the oven light on to maintain the temperature.
* Another method is to turn your oven on and then off again periodically. Be careful that it doesn't get too hot.
* To check the oven temperature, you can put your candy thermometer in a bowl of water inside the oven.
* Other methods for keeping the yogurt warm are: hot water in a sink, stove burner, crock-pot, warming tray, large thermos, heating pad, sunny window, in your car on a sunny day, etc. Just use your thermometer and best judgment.
* The longer the mixture incubates, the thicker and more tangy the yogurt will be.
* Putting your yogurt in the freezer to cool it before to moving it to the refrigerator will result in a smoother consistency.
* Canned pie filling, jams, maple syrups, and ice-cream fudges are good flavorings.
* For a delicious appetizer, use your yogurt to make labneh cheese.
* Using a yogurt maker makes the incubation process a lot easier. It automatically maintains the proper temperature and you don't need to use the oven or watch the temperature. Most come with individual glass jars to put the yogurt in.
* Some food dehydrators, such as Ronco induction type, can be used as yogurt makers too. Read the instructions in the manual.

Warnings

* Watch your temperatures. Don't let the milk get too hot or too cold.
* Old starter won't grow yogurt.
* If your yogurt smells, tastes, or looks strange, don't eat it. Try again with a new batch.
* Get a second opinion on the taste of your yogurt, to make sure it's okay.
* Keep the yogurt still during incubation. Jiggling won't ruin it, but it makes it take a lot longer.