Is it OK to add water during or after primary ?

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Jan 21, 2023
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Week ago I started fermenting plums wine. I use 30 liters plastic fermenters and I have 50 liters beer kegs to use for racking and aging.
I think I filled 30 ltr tank (two of them) with at least 15 liters of fruits (15 liters to each tank), I added sugar syrup and added clean, cold, filtered water to appr 27 liters total.
30 liters tanks have additional several cm high space above 30 ltrs mark, so I left good couple liters room above must in case of foaming etc...
For secondary/racking I will have to fill 50 liters kegs to really full, to get rid of air/oxygen. Then, after each transfer, some wine will be lost (from the bottom).
So I need more and more wine to keep kegs full ! I suppose 15 liters of plums was quite a lot to make total 27 liters of must, am I right ? That should make my wine pretty "heavy" ?
Is that OK to add couple liters of filtered, boiled and cooled water, during primary, or after primary to my 30 liters tanks ??? In other words-can I dilute my wine with water, during or after primary ferment. ?


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Jan 14, 2022
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Hocking Hills, OH
I think the short answer is you can add water whenever. But....
The bulk of the water should be added at the beginning prior to adding sugar, acid, etc. That dilution thing.
Most of us have an assortment of vessel sizes to minimize headspace reducing the need to add any liquid later. And of all liquids to use when reducing headspace, water is probably last on the list.
And you didn't use too much fruit. For most fruit, the more the better. Many use 100% fruit/juice.

Also, headspace in secondary isn't a major issue. The CO2 from fermentation should displace most of the oxygen. In fact, I have gone up to 25% headspace in secondary - but I transfer at 1.020+ so still have a robust fermentation. After secondary, that's different.