A friend asked for my tips on making yogurt. It’s easy but has its quirks.
You will need a gallon of whole milk, a cup of “starter” yogurt (ideally also whole), and a 6-quart instant pot. It’s probably most convenient to start this around dinner time:
Put 3/4 gallon of cold whole milk in your instant pot. Save the rest for your coffee.
Set the instant pot to saute for ~20 minutes, which should get the cold milk to around 180°F. Try not to let it boil, maybe start with 17 minutes and go from there. Check with a thermometer starting around 15 mins.
When it hits 180 or so, put your oven mitts on and take the hot pot out of the instant. Put it on your stove, or a trivet, or somewhere it can cool easily for a few hours. If you don’t remove the pot, it will continue to heat up for a while (and likely boil), and also take forever to cool.
When it’s cooled to between 110° and 100° (it takes a long time!) put the pot back in the instant.
Add 2 or 3 tablespoons (no more!) of plain yogurt (from the store, or from the last time you made yogurt) and stir gently.
You can avoid some lumps by mixing some warm milk with the 2 tbsp of yogurt in a separate bowl before adding it all back in.
Set the instant pot on yogurt mode for 10 hours. Stir it a bit again when you go to bed.
In the morning your instant pot will beep and you will have yogurt. Put it into whatever container(s) you want and refrigerate.
There are many variables of course:
Some people say you will kill all the enzymatic goodness by heating the milk to 180, but I think that’s silly. I mean you’re the biochemical engineer here, do your own research. But if you don’t hit ~180°, your yogurt will have a rough, pebbly texture (ask me how I know.)
Other people say to rapidly cool the heated milk to 100°, I think they’re just anxious. Chill with the chilling.
Regarding the amount of “starter” yogurt: You’d think “hey, a little extra oomph can’t hurt, right?” but you’d be wrong. Bad texture, for reasons I don’t fully understand but have experienced multiple times. Now I’m careful to not over-inoculate.
Your “lots of smaller bottles” idea is fun, I just think it will be challenging to find a way to keep the temps and mixes consistent. Since you can decant into whatever containers you want, I don’t really see much advantage. But if you want to have it set up (become firm) in its final shape, yeah, you’ll need a way to handle temps beyond the IP. Some kind of water bath, maybe?
Like everything microbiological, times and temps are everything.