Lattee's - my milk keeps curdling

[MMMdude]

I have made lattee's at home for years on a Breville machine.  It still works except for the milk frother/heaty thing.  So I started warming up my milk in a microwave and using a hand frother and everything has been fine for months.  Lately though every time I try to heat the milk up it will curdle whenever I froth or even stir it.  This only happens with milk I buy at Walmart.  The milk never smells off and is well before expiry but it will do this curdling thing every single time - it's more than curdling, it will basically turn into cottage cheese before my eyes.  I have tried lower microwave settings and still happens. Any ideas?  Really don't want to start having to buy $6 lattee's at Starbucks.

[olivia]

Don't buy milk at Wal-Mart anymore?

[Greg]

I'm not 100% sure about your method but it may be you're overheating the milk.  Should be warm, not hot, to touch at the most.  Any hotter and you're potentially scalding the milk, and the overheating might be leading to premature protein clumping, if that's the term or even what's happening.  I'm not a foodie or a scientist so I may be full of it.

[shusherstache]

Here are a couple of theories:

Rinse aid causing curdling when milk's heated: http://forums.whirlpool.net.au/archive/2110739

Your milk's almost bad: http://www.home-barista.com/tips/curdled-milk-when-steaming-t14093.html

[steveo]

This happens to me if the milk is close to going off.