First link!

http://www.healingcrow.com/ferfun/ferfun.html

Let me see what I can help you with. First I make my own yogurt SCD style. I like the sour yogurt since I was brought up on European style and the short fermentation cycle used by most commercials is too sweet for me.

I like the Casei Bifidus Acidophilus yogurt starter from http://www.lyo-san.ca/english/yogourmet.html#casei .

What makes this one my favorite is the simplicity in temperatures.
- Heat the milk
- Cool to room temperature
- Add the starter
- Bring it backup (slowly) to 44°C in 12-15 hours

If you are making it strictly for pro-biotic you must stop at 12 hours and leave some lactose or somehow restrict the PH change. Once the sourness gets too high you end up loosing some strength via die off.

Now there may be a way to play with this by using Skim Milk, it would be the exact opposite of commercial yogurt where extra milk powder is added for richness and thickness but the PH actually stalls out the fermentation by killing off the bacteria before all the lactose has been digested.
Now that I thought about it I may try this next...

As for fermentation equipment, here is what I did:

- Get a small cooler
- Drill a hole through the lid, to feed the electrical cable
- Screw a square electrical box on the inside, above the hole
- Mount a 30-40w appliance light-bulb on the electrical box
- Optionally buy a thermostat from eBay and mount that set to 44°C
- Run a test with water to make sure it takes the temp up slowly (change wattage as required)
- Mine is setup to ferment 4L so if I only make two I need to add two water to keep the temperature rising slowly

Of course you can buy a bigger cooler and add a higher wattage bulb, or use your oven.

In India, they heat milk and then add the juice of 1 lemon and let the milk sit out overnight to culture yogurt. Aajonus Vonderplanitz (big raw foodie) makes it by just letting raw milk sit out for about 3-4 days in a mason jar until it cultures. I do this often & don't even add extra starter culture & find it highly digestible...I recommend Claravale raw milk if you live in CA. I work for a naturopath & he has issues w/people fermenting live cultures w/electrical products because it can mutate the bacteria. I say go back to nature & do it the way of the ancients! Obviously, the choice is yours...there is always more than 1 way to do anything. You can also check Sally Fallon's book Nourishing Traditions to read more about making your own cultured dairy. Enjoy!