Started the new chemistry set :)

Might possibly be. There's also probably the fact that you didn't sterilize your corker. Did you also sterilize your fingers before using them to put the corks into the corking machine? (perhaps taking things a bit too far) Or did you just rely on the existing sulphite levels to take care of everything? (I sulphite corks, just as I sulphite cork demijohn bungs by sticking them in a 2 Litre jug and placing a glass plate above them to keep them in the sterilizing solution).

 

Sanitizing is very important but sometimes we all forget something or other and get away with it if we are lucky.
I sanitize my demi's using the water + potassium metabisulphite ( also known as "that powder stuff") . I also use that for the bottles, and pretty much everything else, most of the time too.

 

I just use boiling water.

 

I use Milton sterilising tablets. I half fill my brewing bucket and everything I'm going to use goes in there. I have on occasions forgotten and all has been ok!