Adding Water To Fermenter?

[clay]

I've just put down my fifth AG brew am still have a bit a trouble calculating evaporation and efficiencey rates for my system. As a result I seem to be ending up with less wort in the fermenter at a higher SG than I've calculated for.

Is there any problem with adding water to the fermenter at this stage to get the OG closer to what I want?

Cheers
clay

 

[chovain]

Is there any problem with adding water to the fermenter at this stage to get the OG closer to what I want?

That's what I normally do. Technically, you should use pre-boiled (and cooled) water, but I've always used tap water, and have never had a problem. That'll obviously depend on the quality of your water.

The gravity calculation for how much water to add is pretty straight forward to work out (it's linear), or just use something like ProMash.

Diluted volume = (predilution volume * predilution gravity points) / desired gravity points.

Edit: Keep in mind your beer will come out less bitter than you expected if you don't get your initial calculation right. A higher gravity boil reduces the IBUs. Diluting after the boil will obviously reduce the bitterness further. Anyone know if IBUs are linear with dilution?

 

[clay]

Thanks Mark, didn't think there would be much of a problem.

As far as the IBUs go, a guess it depends on your efficiency, not just evaporation rates. So far I'm flucuating between low 70's to low 80's.

 

[chovain]

As far as the IBUs go, a guess it depends on your efficiency, not just evaporation rates. So far I'm flucuating between low 70's to low 80's.

You're doing well then! Keep in mind that the efficiency calculations are pretty inaccurate (Try adding or removing a single point of gravity in the calculations, and see what it does to your numbers).

The AA uptake depends mainly on the actual boil gravity (which depends more on how much sparge water you use than your efficiency or evaporation). Also keep in mind that most of the IBU calculations ignore evaporation anyway. It's all pretty much guess work, so you're better off just working out what you like, and adjusting your recipes to suit. Unless you get a sample to a lab, you're not going to know what your actual IBU is.

 

[Trough Lolly]

Clay, if you want to hit the exact / target OG, and you're happy to add water to the fermenter and not to the boil, then you can simply put the wort into the fermenter, drop in a clean/sterile hydrometer and add water until the hydrometer is reading the desired OG...Just keep an eye on the temps so you have accurate / adjusted readings from the hydrometer...

Cheers,
TL

 

[chovain]

[...] add water until the hydrometer is reading the desired OG...Just keep an eye on the temps so you have accurate / adjusted readings from the hydrometer...

One thing to be careful of though is make sure you stir if you do it that way. If the water doesn't mix in properly, then it will tend to stay near the surface, making the SG look lower than it really is. It can take a while to get it right if you have to wait for the hydrometer to stop bobbing around

The equation to work out how much water to add is:

Where:

W is the volume of water to add;
V is the undiluted volume
G₀ is the temperature adjusted, undiluted gravity points (e.g. 56)
G₁ is the target gravity points (e.g. 48)
​

This assumes that the water you're adding is 20C (or close to it - It'll be pretty accurate from 15-25C in most cases).

 

[Wrenny]

Big tip - If you're on tank water, you must pre-boil any top up water - filters aren't good enough (failure numbers 1 and 2)

 

[clay]

Cheers for the responses fellas

clay