CMYK to 100% Black in Illustrator

It's not often that I use 100% black in a design, but sometimes there's a requirement for it.  Recently I've been working on a flyer for a new car park in Whitby on behalf of one of my clients.  Having finished the artwork, I sent a PDF version to the printers. 

It was returned with a note suggesting I may want to convert all the 4-colour (CMYK) black to K:100% black, which I did.  The file was then sent backwards and forwards between us a number of times.  Each time I reset all blacks to K:100% but the file always displayed the blacks as CMYK at the printers.

This was quite irritating, and time consuming. 

Finally, this morning, I found the reason why the black wasn't being saved as K:100%.  Illustrator has an option for how black appears onscreen and in exported files, within the preferences section.

I'm certain most Illustrator users will know about this option, but for anyone who's overlooked it (like me) and become frustrated with preparing files for print, I thought I'd make a note.  Here's how to access the Appearance of Black preference:

And here's the dialog:

Just check that the Printing / Exporting dropdown is set to Output All Blacks Accurately, which will retain your defined colour settings rather than the computer overriding K:100% with CMYK black.