Would using milk powder better than fresh milk when poaching? I read this question - What is the effect of poaching fish in milk? and was surprise that one can poach fish using milk.

However, I was wondering if the milk will be spoil if it is continuous being cooked? And also would it be better if milk powder is used instead of just fresh milk?
Poaching is a gentle process - the milk isn't boiling so there is no risk of it burning or the like. It will of course not spoil in the sense of it going off, that's a totally different process.

Fresh milk is better because, well, it's fresh. Powdered milk would probably work, but if you have fresh, use that.