Gravity, efficiency and losses

Every gravity we show comes out of the same piece of bookkeeping. Each fermentable has a yield, in points per pound per gallon. Multiply it by the weight, apply the efficiency that fermentable earns, and you have point-liters of extract. Add them up, divide by the volume of wort they are dissolved in, and that is your gravity. Pre-boil, post-boil and original gravity are the same sum over three different volumes, which is why the volumes have to be right first.

Efficiency is per fermentable

We apply efficiency to each row rather than once over the whole grist, because it is not one number. Mashed grain earns your mash efficiency. Sugar and extract earn none, because they dissolve, and they dissolve completely, so a mash efficiency on a bag of dextrose would understate your gravity for no reason. Steeped grain sits in between.

Final gravity is weighted

Final gravity is attenuation, and attenuation is weighted. We work out what share of your extract each fermentable contributed and how fermentable that extract is, so a grist with a lot of sugar in it finishes drier than the yeast’s published attenuation alone would say, and one with a lot of crystal finishes sweeter. The mash temperature moves it too: a warm mash leaves more dextrins behind, and the prediction shifts with it.

Mash and brewhouse

Brewhouse efficiency is the same extract measured further downstream, in the fermenter rather than the kettle. The gap between the two is not a mystery. It is kettle deadspace, hop absorption, chiller loss and trub, all of which are on your equipment profile and all of which you can measure. After two measured batches, the batch page offers to update the profile from what you actually got.

The beer these numbers come from

Reference pale ale — 20 L into the fermenter, a 60 minute boil.

Grist	Amount	Color
Crisp Maris Otter Pale Ale Malt	4.5 kg	2.8 °L
Thomas Fawcett Caramalt	0.35 kg	9.9 °L

Hops	Amount	Alpha	Addition
Magnum	15 g	13.5 %	60 min boil
Cascade	30 g	6.8 %	10 min boil
Citra	40 g	13 %	20 min stand at 80 °C

It comes out at
Original gravity	1.0507
Final gravity	1.0094
Alcohol	5.52 %
Bitterness	35.66 IBU
Color	5.14 SRM (10.12 EBC)
Into the fermenter	20 L

The numbers

Pre-boil gravity

1.0434 SG, from extract-bookkeeping.

SG = 1 + (Σ kg × PPG × 8.345404 × efficiency) / preBoilVolume / 1000
⇒ Pre-boil gravity = 1.0434 SG

Input	Value	Unit
Pre boil volume	25.83	L
Mash efficiency	78	%

Sources:

• How to Brew — John J. Palmer, Brewers Publications, 2017

Original gravity

1.0507 SG, from extract-bookkeeping.

SG = 1 + (Σ kg × PPG × 8.345404 × efficiency) / postBoilVolume / 1000
⇒ Original gravity = 1.0507 SG

Input	Value	Unit
Post boil volume	22.11	L
Mash efficiency	78	%
Total point liters	1121.7	point·liters
Theoretical max point liters	1438.1	point·liters

Sources:

• How to Brew — John J. Palmer, Brewers Publications, 2017

Final gravity

1.0094 SG, from weighted-apparent-attenuation.

AE = OE × (1 − Σ(extract × attenuation) / Σ extract); FG = SG(AE)
⇒ Final gravity = 1.0094 SG

Input	Value	Unit
OG equivalent	1.0507	SG
Original extract plato	12.56	°P
Yeast attenuation	80.8	%
Net attenuation	80.8	%

Sources:

• Methods of Analysis — American Society of Brewing Chemists
• How to Brew — John J. Palmer, Brewers Publications, 2017

Brewhouse efficiency

70.56 %, from extract-into-fermenter.

brewhouse% = 100 × (OG points × fermenter volume) / Σ theoretical point·liters
⇒ Brewhouse efficiency = 70.56 %

Input	Value	Unit
Mash efficiency	78	%
Volume into fermenter	20	L
Theoretical max point liters	1438.1	point·liters

What it assumes:

• The gap to mash efficiency is kettle deadspace, hop absorption, chiller loss and trub.

Sources:

• How to Brew — John J. Palmer, Brewers Publications, 2017