When does google penalizes sites with THIN content.

So the title of this post says it all.

I want to test out something with content on my already developed site and see if it works, i know that i can test on a new one but i wont have the same results because the old one has DA/PA, TF/CF and its already ranking for some terms...

I want to test some content, i not quite sure if its going to work or not.

So my question is when does google penalizes sites with thin content ? Is that happening when they push an update or from time to time and no one knows ?

This matters to me because if i don't succeed with my experiment i'll just remove/de-index the posts and i'll be fine with the site after that i guess...

I want to discuss this, give me your thoughts.