[djmcmath]

The folks at Whole Latte Love (wholelattelove.com) will ship you a neat-o citrus-based cleaner in any one of a number of varieties designed specifically for removing nasties from aluminum espresso machine boilers. Make sure they know it's aluminum (as many are brass instead) and you'll be hooked up right away. Also might check over at coffeegeek.com to see if anybody can recommend a supplier closer to NZ, as I believe WLL is located here in the States.

FWIW, pumping milk through an espresso machine makes these worse. Orange juice, while citrus, doesn't help either. Vinegar works, but slowly, and it takes forever to flush that flavor through. (sigh) Good luck,

Dan