For many  centuries making yogurt was more o less known practice. But not so long ago before knowledge of prebiotics and probiotics these valuable milk by-products like soured milk was considered bad and not for use except in Slavic and similar cultures milk is used for ages in fermentation. Recently scientist extracted human and animal specific bacterial strains which turn to be very valuable to humans who lost them due to sickness or wrong lifestyle. (see Probiotics).
For example it is known for very long time that strains like Bifidus Infantis is the first to colonize digestive system of a newborn baby and this strain along with other strains are responsible for immune functions as well as creations of other Probiotic Strains and Vitamins. 

Newer strains like L.Rreuteri draw much of the attention in scientific communities due to excellent record in safety proven in more than 200 clinical medical studies 
 

Lactobacillus reuteri proved to be growing well in lactose from milk with addition of some FOS (fructo-oligo-saccharides like inulin). To start succesfuly grow you need:
 

1. 1 tablet of L.Reuteri 46017 Biogaia strains.

2. 1 Liter of milk Pasterized at 82 °C or UHT milk already Paserized at 82 °C

3. 1 tsp of Inulin as a food.

4. Preheat milk in Yogurt machine with adjustable temperature at 43 °C and time of 14 hours

5. Add crushed & powdered  L.Reuteri tablet and add 1 tsp of inulin, mix.well and start fermentation at 43 °C for 14 hours.

6. When Fermentation is finished MOVE DISH TO FRIDGE WITHOUT TOUCH & DISTURBING finished fermented product. Leave it in fridge for approx. 6hours.
    

If you wish you can make Primary batch by making high concentration adding approx. 5 tablets in 1 liter of pasturized milk with 1-2 spoons of inulin.

At the moment best results for growing L. Reuteri show bacterial strain:
L. Reuteri Protectis DSM 17938 & anti-inflamatory ATCC PTA 6475.