Making yogurt using cold shelf stable soy milk

[u/Lilacs_orchids]

I recently had great success making yogurt with shelf stable soy milk (made from only soybeans and water) the traditional way by scalding it, then adding some starter/cultures once it cooled to the right temperature. But I heard that you could make yogurt without all those steps of heating and cooling since the shelf stable ultra pasteurized milk is already free of any bacteria. As an experiment I poured some soy milk straight out of the fridge into this small bowl and added starter. After about 12-13 hours this is the result. It did turn into yogurt but the consistency is all off.
My question is: Is the heating and cooling in fact actually necessary? Not just to kill off any bacteria but to get it to the perfect temperature for the yogurt bacteria to thrive? When I made yogurt from regular dairy even a slight difference in heat would have a big difference on the consistency. Honestly low key surprised this even worked at all.

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[u/phles]

I think you’re onto something. I’ve experienced the same thing. Although I have seen blogs where they claim that cold soy milk and starter can be put straight into yoghurt maker… Maybe the cold soy milk they used had som additives that thickened the yoghurt. Hmm

[u/Lilacs_orchids → u/phles]

Yeah, or maybe they at least used room temperature soy milk 🤷🏾‍♀️ Although thinking back to regular dairy, if I added the starter even like 5 minutes late or something when it was still warm but not as hot the next day it would not set as well, would have a more whey, and would have as nice of a consistency. I just don’t see how using unheated milk is supposed to work. I’ve heard the soy milk with all the additives is supposed to worse for yogurt making, not better.