Just realized that we forgot to put the piece on the airlock that keeps outside air out but lets excess gasses out.
We put the water in and put the perforated plastic lid on - but neglected the little piece that floats in the water over the vent to keep outside air out.
The beer has been fermenting for 4 days (since Sunday evening)
How big of a deal is this? Is the batch worth keeping or is there a good chance that it went bad?