Actually quite easy – I have done this with 4th graders studying the gold rush in California.  What you are doing is capturing wild yeast.  You can experiment by placing jars of milk in different places – your house, a friend across town, etc.  You should be able to taste a difference.

Starter Ingredients:

• 1 c milk
• 1 c flour

Instructions:

1. Place milk in a glass jar or bowl.
2. Cover with cheesecloth.
3. Let it sit for 24 hours.
4. Add flour and stir.
5. Let it sit out in the open (best outside) for 5 to 7 days.

It will get disgusting looking and smell like a winery.  That is good – it is fermenting and that is what makes it “sour”.  The liquid is actually “hooch”.

Primary batter:

• 1 c sourdough starter (from the jar you have stirred a bit)
• 1 1/2  c flour
• 1 c warm water

Instructions:

1. Mix in a large bowl.
2. Cover with plastic wrap.
3. Place in a warm, draft free area for about 12 hours for proofing.  It should get bubbly.
4. Stir.
5. Remove one cup and put back in the starter container for next time.

Use to make biscuits, bread, pancakes, waffles, whatever.

Source:  Ginger Kleerup