Homebrew PCBs

Hello out there!

  I've been experimenting with an old skillet in an effort to develop a 
safe homebrew reflow profile.

  To test my reflow profile, I've been cooking scrap pieces of PCB with 
a small quantity of old RS electronics solder paste on the board to 
check that the solder melts etc.  The paste is best before wk 50, 2003.

  During these reflows, I heat the board to 225C max.  I have noticed 
that the paste forms a crust on the board, which can be wiped off (as 
per Stefans  suggestion)  but am concerned about the crust with respect 
to its affect on component joints.
 
  Does this crust form on in date paste on component joints??

  Thanks for your help

  Trev