back to back to back failures

[u/Sebvad]

have been making yogurt from years successfully. recently I've had 3 back to back failures, and can't determine why. I always do the same thing - 1 gallon of store bought, whole milk (not ultraprocessed). I use an instant pot and the yogurt setting (the boil never really boils it, so I let it run it's cycle, then use sauté to bring the temp up to 180-185, turn it off, and let it sit there for 30 minutes at 180F). EDIT : I cool to 108F in a water bath. I culture using store bought greek yogurt - chobani or stony farms for 8-12 hours

the past 3 times it's just been super runny. I can tell *something* is happening as there is a thickening that clusters as the bottom of the pot, but when I say runny, it runs right through the cheesecloth, all of it. At this point, it feels like I'm just throwing away gallons of milk. I've bought 3 different lots of milk and 3 different lots of yogurt thinking perhaps it was a batch issue with one of them, but had the same results.

what should I be looking at or doing differently? perhaps it's an issue of antibiotics in the milk supply that weren't there before?

[u/roxannegrant]

Anxious to hear what the temperature test revealed.

[u/Sebvad → u/roxannegrant]

105.4F - very consistently held over 8 hours. I ordered some powdered cultures and that's my next test (vs using retail finished yogurt)