Levels of Boiling Wort – Visual Reference for Homebrewers

Define Rolling Boil

The guys from Brew Strong, Jamil Zainasheff and John Palmer, have frequently referred to a “vigorous/rolling boil” followed by some descriptors to help clarify what it looks like. I wanted to find a visual of what they were talking about to define rolling boil, but all I could find were images of water boiling, which didn’t really help.

Here is a humble submission to the world of homebrewing. I’ve created a short video with some easy terms and definitions of the different levels of a boil. They range from level 1 to level 5. The idea is that if more people use these same terms, we’ll all be on the same page discussing the look of a boil without actually seeing it.

You can also see some animated images below the video to define rolling boil.



Level 1: Simmer

  • Occasional tiny bubbles breaking the surface
  • Occasional surface deformations

Level 2: Slow Boil

Slow boil
  • Dense tiny white bubbles coming up with deformations
  • Frequent surface deformations

Level 3: Rolling Boil

Rolling boil
  • Constant tiny white bubbles causing surface deformations
  • Momentary bubble ring around surface deformations

Level 4: Vigorous Boil

Vigorous boil
  • Tiny white bubbles appear all over, not just under deformations
  • Constant simultaneous surface deformations

Level 5: Violent Boil

Violent boil
  • Bubbles break the entire surface
  • Surface deformations occur under previous deformations
  • Deformations are violent eruptions

Boil Over

Boil over
  • Violent eruptions produce persistent foam
  • Foam covers the entire surface
  • Foam and eruptions overflow the kettle


Boil over prevention
  • Reduce heat
  • Stir away surface foam
  • Mist cold water on the surface foam with a spray bottle

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