Calculated ABV with False results due to topping up at secondary?

[TinyRivers]

Hi Folks, has anyone ever figured this out? (I saw nothing on it).

So, I DO presently do two-stage fermentation (I know it's not for everyone), and I've been using the equation ABV% = (OG -FG) x 131 to get a roundabout ABV reading. My question is that it is encouraged to add top up water to your secondary to reduce head space in the carboy, and this also reduces the SG reading. I would have to assume that would throw off the results of the equation, making it look as though the % was higher.

Is there a way to calculate this into the equation to get a better idea what my ABV really is at the kegging stage? I hope I'm clear with my question.
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Thanks for any help, Doug.

[Oginme]

First, I have not seen anyone 'encourage' the idea of topping off your beer going into secondary.  It totally throws off the calculation for ABV as well as the color, flavor, aroma, and bitterness, unless you have counted on that in your initial brewing.  I do know someone who deliberately brews their beer at 2x strength they want it to be in the end and then dilute it when putting it into the keg, but it is not something I would recommend unless you have experience doing it.

Since you don't have a final gravity of the beer before diluting it, you won't be able to just do a straight dilution calculation.

Getting back to your question, the way to "calculate" your approximate ABV is to open up your recipe in BeerSmith, plug in the amount of water you added into the "top up water" in the fermenting/bottling section of the 'volumes' tab.  Now go back and change the amount into the fermenter on the design page to be the original amount PLUS the volume you just added to the "top up water".  This should give you a fairly good idea of the resultant ABV.   

[TinyRivers]

Thanks for the quick reply. I've yet to top the carboy. Don't think I will, but I know it can be a concern for oxygenation.
Regarding the Beersmith changes, I guess I thought the top up field was only referencing your intial top up going into the primary. I'm extremely green to Beersmith but I like it a lot...I'll take another look and see if I understand where you are referencing in the program.

Again, thanks for the info. Doug.

*Still not sure I'll top up though, I'm using a 19l carboy but still lost enough to barely reach the beginning of the bottleneck. You figure I'm worrying to much about the oxygen?

[Oginme]

The exposure to oxygen is one (of many) reason that I only transfer to secondary if adding something odd to the fermenter, often fruit or wood.  If you transfer while still having appreciable fermentation left to go, then the yeast in the beer will scavenge much of the oxygen in the head space.  Yeast just love to create sterols from the oxygen to add to the strength of their cell walls.

Your idea of how the 'top off water' to the fermenter is correct in its original intent.  I just used its existence to rework the numbers to give you some idea of what you would end up with for final ABV and other stats using the software.  Since the numbers in the modeling are not fixed, it is critical that you reflect any addition to the 'top off water' to the batch volume to have it reflect the impact of your actual move.  If you don't make this move, the program will adjust the mash efficiency to meet your fixed brew house efficiency and give you a false estimation.

[TinyRivers]

Perfect, thanks again Oginme, you clearly know your stuff. I'm certainly looking forward to better understanding the process and the program. Cheers, Doug.