In this step, prepare the lid:
- Cut out a circle of cotton fabric.
- Use a larger plate as a template.
- Cut using a razor blade.
Secondly, remove the upper part of the lid:
- Use a drill press / mortising bit.
- Sand rough edges with a rough sponge.
This is necessary to allow the kombucha / water kefir to "breathe". If this step is omitted, condensation may form in the jar which would be a perfect environment for mold to grow. If you have a serger or are married to someone kind enough to serge fabric for you, serge the edges of the fabric.