In a glass/ceramic bowl or a glass jar, mix 2 tablespoons of Prebio Plus with the contents of 1 tablespoon of L. gasseri yogurt and 1 tablespoon of L. reuteri yogurt.
Stir in 5-6 tablespoons of milk. Mix well with a spoon or whisk to avoid clumping. Do not blend. The result should resemble a slurry. Stir in the remainder of the milk. Mix well with a spoon or whisk for even distribution. Do not blend.
Place in jar and cover lightly with plastic wrap or loose-fitting lids. Don't remove the lid during fermentation to avoid getting a yellow or pink discoloration on the top of the yogurt. This is a harmless yeast that might affect the taste, so scrape it off the top of the yogurt before consuming it.
Place in a yogurt maker or appliance that ferments at a constant 97°F - 100°F for 36 hours, away from the airflow of air vents/heaters/air conditioning, etc. Do not stir while fermenting.
Remove yogurt from the appliance, keep the lid loosely on the jar, and refrigerate. Tightening your lids while the yogurt is still warm may build up pressure and cause your glass jars to break. Once the yogurt has chilled in the fridge, then you can tighten the lids. Refrigerate for up to 4 weeks.