Ended up with too high gravity wort. Since I was not prepared for this I didn't have enough sterile water to dilute the wort. I ended up pitching the yeast anyway and adding sterile water at 11 hours later. At this point the yeast was fully activated and regular air had probably left the tank. While being cautious about splashing, more oxygen most certainly ended up in the fermenter. In a about 15-20 minutes the airlock started letting air out again.

  • What should I be on the lookout for now? I assume there is a risk of contamination, oxidation and diacetyl production.
  • Has anyone else a attempted this, and how did it end up?

Normally I would have changed the fermentation schedule and swapped the style, but this was not an option with this one. The combination of IBU and color would have beer through the roof for any sensible style. Additionally there was a limit for how long it can sit and ferment.

EDIT The wort was diluted to the 122,5% of the original volume from OG of 1.100 to 1.082. Using Vermont Ale Yeast that typically attenuates to 1.018 (expecting ABV of 8.39%)

3 Answers 3


You can safely dilute at any stage.

Contamination is probably the biggest risk. But just takes basic sanitation practices to avoid.

Oxydation: Really only an issue if 50% or more of the alcohol is present. Just don't splash, use a tube to add water below the wort surface.

Diacetyl: It isn't an "infection" it's produced by all yeast during growth phase but then later reconsumed by the yeast. Holding temp at 68° late fermentation cleans this up (Diacetyl rest).

What to dilute with: I would recommend the same water profile to be used if you can get it in early to fermentation. If adding very late or to finished beer distilled water tends to work well. Never use chlorinated or chemically sanitized water.

What to expect? Sounds like a good Double IPA.

  • Indeed a Double IPA :) I use a different malt bill for Barley wines.
    – Martin
    Commented Mar 19, 2018 at 16:19

Regarding contamination, if you boil the water you are using to dilute and let it cool in a sanitised pot, then add it you should avoid bacterial or wild yeast contamination.

At that OG (1080) don't worry about oxygen, if anything your yeast will need more of it due to the high starting gravity. When I do 1080+ beers, I often open the FV after 24H, to let out CO2 and let some air in, but keep the lid over the vessel to stop anything falling in, then give the FV a good shake to get more oxygen into solution.

At high gravities your yeast will need more oxygen, and a little extra from adding more sanitized water, or popping the top for a look or sniff will often benefit rather than hinder your fermentation.

  • 2
    +1 for pointing out high-gravity brews often need extra oxygen. Some companies even make devices for adding it to the fermenter. In fact, some very unpleasant off-flavors are the direct result of yeast that hasn't been given enough oxygen to thrive.
    – thanby
    Commented Mar 19, 2018 at 17:10

At what gravity did it started and what was it when the water was added? If the fermentation only just started and still has a long way to go, oxidation would most likely not be a problem. Also the risk of contamination would be minimal I guess. Tab water itself is usually very clean in terms of bacteria (in most western parts of the world at least ;). For example, there are kits where you just have to dilute the extract with water straight out of the tap and add the yeast...

About diacetyl, no idea. I can imagine a higher gravity wort does have a different effect on yeast and thus give off flavours when diluted later. But again, it is still early in the fermentation so this would be minimal.

  • OG of 1.1 diluted to 1.082. Amended original question with more information just now.
    – Martin
    Commented Mar 19, 2018 at 10:19

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