Mold in Your Cold Brew Maker: Causes and How to Fix It

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Why immersion cold brew makers are prone to mold

A damp felt filter, sitting at room temperature, holding trace amounts of organic coffee residue, is close to ideal conditions for mold growth. It’s a common complaint with any immersion cold brew system, not just the Toddy, but it’s almost always preventable.

The most common cause: sealing a damp filter

If you rinse the filter after brewing and immediately store it in a sealed bag or closed container while still wet, you’ve created a small greenhouse. Always air dry the filter fully — usually 12–24 hours in the open air — before putting it away.

If you already see mold

  1. Discard the affected filter if the spots are dark, fuzzy, or don’t lift with cleaning — felt filters are inexpensive and not worth the risk of an unclean brew
  2. Wash the brewer body, decanter, and rubber stopper with hot soapy water, then a diluted vinegar rinse (1 part white vinegar to 4 parts water) to kill any remaining spores
  3. Let every part air dry completely before reassembling

Prevention going forward

  • Rinse the filter immediately after each use
  • Deep clean weekly with a baking soda soak (see our full cleaning guide)
  • Store the filter somewhere with airflow, never sealed while damp
  • Replace the filter every few months even with good care

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