Missing recipe for soil bag

So I finally assembled a toilet (yay!), and collectes some poop (ew!) and I have biomatter and plastic, but I have not gotten the recipe to make soil bags (which I have collected a handful of).

​

To clarify, I i have the recipe in my workbench, and it shows biomatter, and an undiscovered item in the second window.

​

Is there someone I meed to talk to or an email or something I need to read?