Ask Mr. Wizard

Boil Timing


Kevin Dill Via Facebook asks,

Does the amount of time it takes to get the wort to a rolling boil have a negative impact on the brew itself, or not?


In a very general sense the time required to bring wort to a boil can cause problems when the time is too long. Holding hot wort for extended time periods leads to heat-related chemical changes, generally termed “thermal stress”. But in a more practical sense this is not normally associated with waiting for the kettle to boil for one very simple reason; evaporation rate.

Brew kettles are designed to boil and evaporate water from wort during boiling. Traditional, some would argue outdated, kettles are usually designed to evaporate about 8–10% per hour. More modern designs focus on reduced energy consumption and thermal stress during boiling, and the evaporative rates in these designs is usually around 4%. So how does this relate to kettle heating time? In order to achieve these evaporative rates a certain amount of energy must be supplied to the kettle and this amount of energy is plenty to heat the contents of the kettle to the boiling point during wort collection.

In practice, brewers do want to get the wort boiling as soon as possible to save time and also not feel like too much time is spent looking at a pot of wort waiting for it to boil. It does help to have a burner that can be cranked up for the heating stage and then dialed back once the wort begins to boil. If the burner is too small to get the wort boiling within 30-45 minutes of kettle full I would look for a larger unit that can provide more heat. One practical method used by most brewers during the brew day is to begin applying heat to the kettle during wort collection. If this is timed right the boil begins just about the time the kettle is full.

Response by Ashton Lewis.