From: "John Moody"
That would be a 'usual' way to do it, but according to the photographer (Irene Müller), it's not what she did:
"BTW, I don't use any sound/photogate triggers for my high speed photography. Just a pipette or syringe, good eye/shutter finger coordination and patience, patience, patience..... "http://www.pbase.com/daria90/milk_meets_coffee_splashesThat makes it that much more impressive. There are also some more coffee images at that link, along with some other galleries that I think are very good.