How to Clean and Sterilize a Demijohn for Homebrew

Sterilizing and cleaning your demijohn between each brew is the most important thing you can do to ensure high quality and consistent brews. It’s a simple process but can seem a bit complicated for someone starting out. 

Note: this Guide is only for Glass Demijohns, if you are using plastic (PET) please follow this guide

Carboy One Gallon Glass Jug & Hand Homebrewing Beer A carboy one gallon glass jug containing a freshly made beer mixture ready for fermentation. Home made on a gas range carboy glass fermenting demijohn stock pictures, royalty-free photos & images

Basic Overview:

As the title of this article suggests, it isn’t simply enough to just rinse out your demijohn and go again. We instead need to follow a two-step process this involves Cleaning (fully removing any residue) and then Sterilizing/Sanitising (removes microbes). This needs to be done in this order. The aim of this process is to kill any bacteria, residual and wild yeast and ensure a predictable ferment. Luckily these days there is lots of handy products to help make this a lot easier.

What you’ll need:

For Cleaning:

  • Warm water
  • PBW or Sodium Percarbonate or OxiClean Free (unscented)
  • A demijohn brush

For Sterilising (Sanitising)

  • Star San/Chemsan (or bleach if you’re really stuck)
  • A drying rack or clean surface

To Sterilise 

 How to do it:

1. Clean the Inside Thoroughly

Use:

  • PBW (Powdered Brewery Wash)
  • OxiClean Free (scentless)
  • Sodium Percarbonate

Steps:

  1. Rinse out with warm water (not boiling)
  2. Add 1–2 teaspoons of your chosen cleaner into the demijohn.
  3. Fill with warm water.
  4. Let soak for 30–60 minutes (or overnight for stubborn residue).
  5. Swirl and scrub the neck using a demijohn brush.
  6. Rinse very thoroughly—no cleaner should remain.

 

2. Sterilise (Sanitise) the Demijohn

Use:

  • Star San/Chemsan (no-rinse, acidic sanitizer)
  • Milton/bleach solution

Steps:

  1. Mix Star San/Chemisan to ratio on instructions
  2. Pour into the demijohn and swirl to coat all surfaces.
  3. Leave for 30 seconds of contact time.
  4. Pour out the foam (don’t rinse)
    (The foam is completely safe for fermentation.)

 

Bleach Method (If you have nothing else)

  1. Mix 2 tablespoon (30 ml) of plain bleach per 5 litres water.
  2. Fill the demijohn and let soak 20 minutes.
  3. Rinse 3–4 times with boiled/cooled or filtered water to avoid off-flavours.

 

3. Let the Demijohn Drain

Place upside down on a drying rack or clean surface.

Final Words:

As you can see, this isn’t a complicated or expensive process, its just one that needs to be done right. Once you've mastered sterilising your demijohn, you need to sterilise your bungs, bubblers and other bits too, Click here to view that Post.  Hopefully with this guide you’ll have all the tools you need to get you’re brews safe and sanitary!