Adding cool water to wort after the boil

I started with brewing small kits from Craft-a-Brew. They have you start with 1 gallon for the boil and then add cool water later on if you need more to make the full 1 gallon in the fermenter.

I was thinking… they didn’t specify that this water be boiled, and therefore pasteurized. When using that method, did I just get lucky, or is it really ok to just add filtered, unboiled water to the wort?

The water you add only needs to be sanitary. Generally tap water is sanitary. You don’t want to add water from a municipal supply though without treating it. All municipal water is treated with chlorine or chloramines. This can give a band aid flavor to your beer. Campden tablets will remove the chlorine and chloramines. One-quarter tablet will treat five gallons.

Chilling the top off water will cool the boiled wort.

Sanitize the container you collect the top off water in so this doesn’t become a source of contamination.


It seems like it’s a decent way of speeding up the cooling of the wort to yeast-friendly temps.

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You can also freeze the top-off water.

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If you are topping up with water after the boil and you are worried about its sterility, do yourself a favor, save yourself some time, and top up with commercially acquired ice. In CA at least, commercial ice is regulated as a food product. The plants that produce it are tested weekly and their bacterial load is supposed to be 0, like none. The trick to this is two-fold, figuring out how much ice is equivalent to the amount of water you need to top up with, as well as figuring out the thermal effect that this much ice is going to have once you dump it into your system. Two ways to figure out how much ice=how much water. Either weigh the ice and do the math, or put it in a container and let it melt down, then you will know from then on how many of those same containers to add to the hot wort to then get your full batch once it has melted. I like weighing it. The second part of the trick is knowing what your required amount of ice is going to do thermally to your batch once the hot wort and ice are combined and it’s a little trickier and involves some basic algebra. It also involves consistency, and I will explain with an example. This is what I have been doing lately now that the groundwater is warming up in CA and I find it more and more difficult to cool my batches with my immersion chiller. When I want 16 gallons of finished wort, I plan on brewing 11 gallons, cuz that’s what easily is boiled in my converted keg cook pot. I adjust my S.G. and hop schedules to reflect the fact that I will be diluting with an additional 5 gallons of ice and water (this is a whole other topic and we won’t get into it here) to top up to my desired 16 finished gallons. From experience I know that 28lbs of ice mixed with the necessary water(water roughly 70*) has a thermal effect of -64. I then do my math depending on what temp I want my wort to finish at in my fermenter. Here it is, hope I haven’t lost you yet. 11g(X*) + 5g(-64*)=16g(70*) X is the temperature I will need to get my wort to in my kettle before transferring it to my fermenter where the 5 gallons of ice and water is waiting to cool what will end up being 16 gallons total at 70*. If it’s not 70* and I am doing a lager, or whatever temp it is, just change the number to whatever you want it to stabilize at

Sorry. Pressed the wrong button. Anyway. To finish this thesis. In the above equation I know from doing the math that in order for my wort to stabilize at 70* I need to cool the 11 gallons in my kettle down to 130.9, which is easy to do in a short amount of time even with the warm CA groundwater. What you have to do is figure out how much ice you will be using each time you cool in this fashion. After the first time, you can do the math in reverse and figure out exactly what the thermal nature is of the amount of ice you plan to use, combined with the intracasies of your particular system. I am sure it will not be -64, but whatever it is it will be consistent each and every time and by doing the math you will know exactly what temp you need to get your wort to in order to hit your target temp of your total volume. Did all of that just make sense??? I love this trick by the way and it’s been shaving lots of time and energy from my brew day.

Yes that makes sense, but I’m only doing 1 gallon batches…so it’s not that complicated yet :wink: