I'mm assuming it I wanted to convert a sourdough recipe to using IDY I would simply keep hydration levels the same, assuming the sourdough being 100% hydration, use the recipe as written add add IDY. The trick may be figuring out how much IDY to use.
Am I on the right track??
Many yeasted bread recipes use a packet of instant or dry yeast for about a pound (say 350 - 450g) of flour. That's usually said to be 2 1/4 tsp (US teaspoons, other may be a little different). You can use less and the fermentation time will get longer. You can mimic some sourdough fermentation schedules by using 1/4 - 1/2 tsp instead.
Don't be surprised if the flavor of the yeasted bread seems flat or lacking compared with the sourdough. The difference will seem less for highly enriched doughs.
TomP
I understand the flavor difference of course, I'm only asking if I'm on the right track for the substitution.
The "hydration" of the bread would be the same. Start with less starter and go from there. I would keep a close eye on it till you get what you want. Enjoy!
I use around 2% yeast to flour weight. For 350g flour, which is my standard loaf, I use 6-7g of yeast. That jibes with Tom's figures and you can use less for longer ferment, as he said.
Don't forget when you're converting the sourdough recipe to add all the flour & water in the starter back into the main dough. Chatbots are really handy for that sort of thing. Ask AI to convert the recipe from starter to yeast, listing the quantities involved. For example, 400g flour with 20% levain at 100% hydration, total loaf hydration you want, etc. It will do all the work, as long as it knows the percentages. You could probably just say convert this recipe from starter to yeast and type in the whole recipe without any percentages. It will figure them out from the original recipe.
I got AI to convert a yeast recipe to starter by telling it total hydration, starter hydration and what % of starter to flour I wanted to use. Turned out fine. I also threw in % of yudane as well. Piece of cake for a bot.