I made the HopNog kit from Brewer's Best, but added liquid yeast instead of the dry that came with the kit. About18 hours after pitching yeast, NOTHING was happening--no bubbling airlock, no krausen no nothing. Threw in the dry yeast and aerated. Twelve hours later, I'm the airlock is bubbling pretty well--about once every couple of seconds. What are the chances that my wort got infected prior to the yeast establishing themselves?