It’s difficult to reach the desired quantity of wort when homebrewing from the first attempt as some water will always evaporate out. Sometimes, brewers don’t own a brewing vessel big enough to brew the full batch at once and they need to top it later.
In either case, it’s possible to add water after the boil and before the fermentation starts to reach the right quantity just as it’s possible to add water later during the secondary fermentation but this must be done carefully as it could infect, oxidate or introduce chlorine into the brew.
I always had this problem as my brewing vessel only holds 5 gallons and I was always brewing 6-gallon batches. In this article, I will explain what’s possible and what might hurt your homebrew regarding the later addition of water.
Things to have on mind when topping off with the water
1. Always purify and boil the water
No water straight from the pipe should ever be added to the wort or finished homebrew. There’s always a risk of infection at any stage if you don’t purify the water and pipe waters have high levels of minerals or chlorine (really bad for the taste) which definitely shouldn’t end up in your homebrew in any high amount.
This is why you should bring the unpurified water to the boiling point of 212°F (100°C) and keep it there for at least 15 minutes.
In case you are using distilled or bottled water, they are already purified and as such there shouldn’t be a risk for infection.
Plus, prior to fermentation beginning even if there are some light microbes, the healthy yeast culture should easily overwhelm it.
Distilled water is good for topping off your fermenter, as it simplifies things but it should be by no meaning used as the primary water source for the entire wort as it doesn’t have sufficient mineral structure. This is the reason why if you brew with distilled water it’s important to add those minerals to the water prior to starting the mesh.
Bottled water on the other hand contains essential minerals and has a healthy ratio which is nice for brewing purposes!
2. Original gravity will change
When you add top-off water you will change the original gravity, so be careful that you don’t add too much but also don’t skip this step if you previously used a higher concentration of malts and hops as you really want to nail the original gravity and final gravity.
In case you added too much water refer to the linked article where I explain how to fix things.
Being perfectly accurate is not easy and it’s not the most important task for beginner homebrewers yet the closer you are to the gravity readings before and later the more authentic the recipe will be.
It’s also important to read the original gravity with hydrometer once the top-off water’s been added because when you take readings at the end of fermentation this will give you a clear indication of how dry you managed to get the brew to (in other words, how effectively yeast did its job at converting sugar to alcohol).
3. Introduction of oxygen
The addition of top-off water will introduce extra oxygen which is also nice prior to the fermentation but is the worst nightmare after the fermentation.
Even with rigorous boiling, the oxygen is hardly removed and it’s impossible to completely get rid of it as it will always return back into the water when it cools. The ideal method would be to use a keg and purge it with nitrogen or Co2 as the linked study suggests.
If you want to remove oxygen with boiling, at least use the water as soon as it cools down as it won’t have time to absorb too much oxygen.
4. It must be mixed
If you plan to add water to the secondary be careful how you mix in the water, so use the same principle as you would with the priming solution. It should be gently introduced into the fermenter and only slowly stirred without causing a disturbance or touching the bottom of the fermenter.
Prior to fermentation, it’s recommended to give the wort a stir or a shake when you add top-off water because the pure water will have low density while the wort will be high in density, and without a stir or a good shake the wort won’t combine nicely.
This is easily done, so just stir it a bit or do this during the aeration because that’s when you’ll shake the wort anyway.
Adding water to the wort after the boil (Before Fermentation)
You can add water to the wort after the boil before the fermentation begins as it won’t hurt the brew as long as the ratio is good.
Before the fermentation begins, you’ll want to reach the desired quantity, cool it, pitch the yeast and aerate the wort.
If you just finished with the boil you should transfer it to the sanitized fermenter and top it with additional water as soon as possible, stir it to mix all ingredients together, and let it cool.
Water will always carry some oxygen. Any addition of water prior to fermentation is less dangerous than it is after the fermentation. This is because if you introduce oxygen prior to fermentation it will be helpful as the yeast needs some oxygen to thrive, yet introducing oxygen after fermentation is bad as it may spoil the brew.
Adding water after primary fermentation (Diluting)
Adding water to a secondary fermenter (or prior to transferring from the primary) is possible but homebrewers should be careful with this practice as at this stage adding more water to the already fermented brew may lead to oxidation or even infection.
Any brew that is fully fermented is at risk of oxidation as oxygen is only welcomed prior to fermentation, so it should be limited or completely avoided in later stages. The additional water homebrewers add to the secondary will carry oxygen and simply pouring it into the fermenter may ruin the brew.
Of course, boiling will purify the water and thus the chances for infection will be gone, but it’s important to ensure one more step to get rid of the oxygen.
You first need to boil the water at 212°F (100°C) for a minimum of 15 minutes to reduce the oxygen, yet the water needs to cool and in the meantime, the oxygen will start getting back in. So, you should either use the water as soon as it cooled, so it has only re-absorbed a little bit of oxygen (which still isn’t ideal) or you need to use the help of Co2 or nitrogen.
How to reduce oxidation?
So, you’ll never completely remove the oxygen from the water by boiling, so for the best results, you should push the Co2 into the water as it will push the oxygen out and won’t let it back in. You can simply spray some Co2 into the water prior to the use but ideally, you would use a keg, fill it with the preboiled (or distilled water) cooled water, and push Co2 in (or even better, purge it with nitrogen, but who has nitrogen at home for this purposes). The water can stay this way for a long, long time without any chances of oxidation.
Adding such water from the keg would be ideal regarding the fear of oxidation, but if you don’t have a keg and Co2 you will have to risk some oxidation into your secondary.
Final take on
It’s difficult to do everything pitch perfect in homebrewing, so even during the bottling from a fermenter with a pipe or a spigot we introduce some oxygen, yet it doesn’t destroy our brew unless it was done vigorously and oxygen was introduced in other stages as well.
But yeah, these details are the reason why sometimes homebrews taste a bit weird, yet still good, so there is always room to improve to make the next batch superb by learning from small mistakes!
You can also drink the brew before the oxidation takes place as the longer the oxidated brew conditions, the worse the consequences, so hurry up!