I agree with QldKev in that it would be overkill for what you wanted to do. It could definitely be done but you'd want to remove the PID code and put a cycle delay in there to save the compressor on your fridge. You'd also have to use another pin as an output to trigger a heating pad if you ever need to heat your brew., which I'd imagine around Wodonga you would!! This could be the pump output circuit, but make sure you set it up for a 240V load. Basically I think you'd end up rewriting the code to replicate a STC-1000, but don't let me put you off!! I've built plenty of things in the past that have cost me more and taken a hell of alot longer to complete than just buying one off the shelf. Half the fun of brewing is building things!!
Cheers,
BB