During the boil a lot of water is evaporated off. I have a 30L boiler and generally end up with around 22L in the fermentation vessel. After racking off from the fermentation and leaving the trub behind I can end up with as little as 19L worth of beer.

To increase the amount of beer at the end or to intentionally reduce the ABV I occasionally add water (same sterile water used for mashing) to the fermentation vessel just before pitching the yeast.

What are the effects of adding water at this stage? Pros vs cons.

Follow up question. I intend to upgrade my equipment in the future. I have 30L kegs I use in my kegerator so 30L is the target batch size.

What is the difference between the above method of adding water to get up to 30L vs having a large enough boiler which can boil down to 30L? Is one better than the other, if so, why?


3 Answers 3


If you have designed your recipe to account for adding the extra water at the end of the boil, then I see no issues what so ever.

I would personally add a couple of litres of boiling water every 10 min or so rather than adding it all at the end, just to avoid over concentrating the sugars in the wort, which may encourage caramelisation & Maillard reactions and hamper hop utilisation. However, it depends what you want from the brew, these may be desirable in your brew.

  • 1
    This is what I do too. Works nicely.
    – Martin
    Mar 23, 2018 at 7:03

There are two potential, but not serious, issues with boiling the volume lower than full: 1. Maillard reactions (not caramelisation) at higher wort gravity tend to be more prominent. Sometimes it's good (e.g. when you boil down first runnings when making dubbel), other times not so good (witbier and other light stuff). 2. Hops tend to be under-utilised in smaller volume boil. This is a common-sense based wisdom, but kinda difficult to measure.

For these reasons boiling the full volume is more predictable.

I like to streamline my brewing processes as much as possible, hence find preparing extra sterile water for diluting wort an extra trouble (btw you don't need sterile water for mashing, just tap water - corrected for chemistry - is good enough). If I were you, it would be getting a bigger kettle (in fact, I have 50l one).


I add nearly freezing water to chill it quicker to pitch temperature. 1 gallon of near frozen I add to 4 gallons of wort to chill it to lager pitch temperature quicker. Once my immersion chiller cannot reduce the temperature any further, I introduce the near freezing water into my wort. I do not notice any negative effects. The hops are still very nice tasting.

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