Storing/Freezing milk

Al

I have QUESTIONS.

I read up on proper storage of breast milk and the rules are very confusing to me. So I need help understanding.

Rule: don’t mix milk pumped on different days. (Why not???)

Rule: don’t add fresh milk to milk already in the fridge. Fresh milk must be refrigerated before combining with other refrigerated milk. (Why?)

Also I need help understanding this lipase business. 🤷🏻‍♀️