My question is regarding which volume to use when calculating OG, and more importantly why.

How to calculate the gravity points for a recipe is fine, but then according to BeerSmith at least, you should divide this by the into fermenter volume, and that is what puzzles me.

When boiling, water evaporates and that will cause the gravity to go up. When boiling is done, when the solution is chilled down, it will shrink by around 4%, and this is also a part that reduces volume, while still containing the same amount of sugars, so this will also make the gravity higher. So far, all good.

But now we transfer from kettle to fermenter, and the loss here should not affect the gravity of the solution, since the loss would be both water and sugars.

So my question is then basically: why should I use into fermenter volume, and not post boil after shrinkage volume?

EDIT My question is regarding estimating the OG, not doing a OG reading when actually brewing. When measuring the OG, it does of course not matter if I do it just before or just after I transfer to the fermenter.

1 Answer 1


OG = Original Gravity

SG = Specific Gravity

FG = Final / Terminal Gravity

OG is usually just in reference to a pre fermentation starting gravity, but can be labled OG for any formula that uses a before and after gravity.

OG for ABV calculations can be taken at any point once concentration or dilution has been done post boil. It's actually most accurate after post pitch and mixed, if including a large volume of the starter wort with the yeast pitch.

Beersmith has into the fermentor and post boil volumes only to calculate brewhouse efficiency concerning total volumes. For line loss, leaving behind trub in whirlpool etc.

A pre boil gravity (SG) is used to calculate mash effeciency and is the "OG" in boil concentration formulas.

  • To make the example a bit more extreme. Let's say that after I am done boling I have 30 liters of beer, but my process of getting beer into the fermenter is a bit "unefficient" so only 10 liters ends up in my fermenter. Wouldn't the OG calculation be way of if I ended up by using 10 liters when calculating since that is the into fermenter volume, when 2 thirds of the fermentables are left behind as trub. An extreme example of course, but just to make my point clearer. Commented May 30, 2016 at 21:16
  • Just so we are sure we are talking about the same thing here, I'm talking about estimating the OG, not doing a OG reading when actually brewing. Commented May 30, 2016 at 22:04
  • For estimating OG yes it will effect it, Beersmith will assume it's boil off and concentrating the wort rather than an equipment loss unless the loss is added to the equipment profile. But your boil rate should be there too. Commented May 31, 2016 at 2:52
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    Beersmith is terribly annoying in its latest iteration as its centered around brewhouse efficiency rather than just mash efficiency. Leads to lots of confusion and you need to pay extra attention to several little volume losses. I wish it gave you a choice to either simply deal with mash efficiency or brewhouse efficiency. I think for most homebrewers mash efficiency is sufficient. My losses to pump and tubing etc etc isn't always consistant and I find myself back calculating to be sure what I measured in the fermentor actually agrees with beersmith. Good answer though.
    – brewchez
    Commented May 31, 2016 at 10:38
  • That's what I'm missing then I guess. That the brewhouse efficiency takes all losses untill fermenter into account, so regardless of what parameters I choose, and long as brewhouse efficiency stays the same, that means that the calculation will always yield the same result. Thanks for adding the comment that gave me the last piece of the puzzle. Commented May 31, 2016 at 21:28

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