Note: This recipe is specifically written for the Instant Pot brand electric pressure cookers that come with a Yogurt setting. If you have another brand of pressure cooker that indicates it has a yogurt function, follow those instructions regarding what buttons to press, sealing the pressure valve, etc.
Timing: I like to start my Instant Pot soy yogurt in the morning so it will be done by bedtime. Then I store it in the refrigerator and it's cold by morning. I don't cook the homemade soy yogurt overnight because then the yogurt would be warm when I needed it since I eat it for breakfast. If you're making it well in advance of when you'll need it, you should be good to make it overnight if you prefer.
Prep the soy milk: Take your unopened package of soy milk and shake it for 10-20 seconds before opening it. Pour most of it into the jar until you've reached the very bottom ridge near the top of the jar. This should be about an inch from the top of the jar. I do not fill my jars to the top because every time I've tried the yogurt has not turned out. You will have a bit of soy milk leftover. You can drink that or store it in the fridge to use later in a cooking recipe, a matcha or coffee drink (soy milk froths well!), or a smoothie such as my green smoothie. If using multiple smaller jars: If you're using a few smaller jars, please follow these instructions. Pour the soy milk (about 28 ounces of it) into a 4-cup glass measuring cup or, even better, and 8-cup glass measuring bowl with a spout (any bowl will work but it's much easier in a vessel that has a spout. Empty the contents of the probiotic capsule into the soy milk and whisk the powder into the soy milk until well combined, about 30-60 seconds. Pour the contents into each of your jars, leaving about an inch of free space at the top of each jar. Proceed to step 6.
Add the probiotic: Over the jar of soy milk, carefully open the probiotic capsule and empty the contents into the jar of soy milk. Place the lid on tight and use both hands to shake it well for 30-60 seconds. Remove the lid before proceeding to the next step.
Prep the Instant Pot: Add the jar(s) to the Instant Pot without lids. Try to place them in the center of the Instant Pot, but don't worry if you have multiple jars and they don't all look level. Place on the lid and tighten it. Set the pressure valve to 'sealing' and press the 'yogurt' button. Press the '+' button until you get to the desired amount of warming time. I have experimented a lot and found 11 hours and 30 minutes to be the sweet spot for us, but you might need to experiment a little too and find your perfect amount of time.
Store: When the timer is up, promptly remove the homemade soy yogurt from the Instant Pot (do not allow it to sit overnight after it's reached it's programmed time, as that may encourage bad bacterial growth). Switch the pressure valve to 'venting' and carefully remove the lid (for me, there's never been pressure buildup, but just be abundantly cautious whenever using a tool like this!). Remove the jars of homemade soy yogurt, add the lids, and place in the refrigerator for up to 5 days. Note that if they are still liquid, they will not thicken in the fridge and they need more "cook" time. See the troubleshooting step below.
Troubleshooting: If the timer goes off and your Instant Pot soy yogurt is still liquid, set the timer for another hour. It should be good after that. If it is still not working, you may have a dead probiotic capsule. Try again with another capsule or a new bottle/package.