Kefir

Kefir is drinkable yogurt. It has long history and lot of benefit for your system.
Check here for more info.
This picture is kefir grain, I bought from internet. If you are interested, I'll give some to you, just let me know.
To make kefir:
Put one table spoon kefir grain (more or less) to a glass jar. Add a cup of milk in room temperature for 12 hour or so. Then drain the kefir (thick milk) to a bowl, it is ready to drink. The kefir grain is for next batch.

Each day the kefir grain grows. You can give it to friends whoever is interested. And you can do something with it (search the web).
You can use more or less milk depends on how much you will consume each day. I usually let it stay in room temperature for 24 hours. I drink the kefir in the morning, and then I rinse the kefir grain and make another cup for next day. Don’t use metal for the process (I don’t know why).

When you drink the kefir, it is sour; you can add some fresh fruit, resins, cranberry, nut or honey for taste. Be creative, add whatever you feel like.

If you want to take a break from making kefir, just add some milk to kefir grain then put the jar to refrigerator. It can keep long time. I did it for several months