help me understand attentuation

[zirb]

Recently finished a beer that finished very low - final gravity was 1.008. (estimate was 1.012) It started low too. Original gravity was 1.045 when it was supposed to be 1.054.

I'm wondering , if I had hit the target original gravity of 1.054 by boiling longer or adding DME would the final gravity have been higher as well? Or would it have still come down to the low 1.008 number?

The specifics:
All Grain BIAB MocktoberFest:
- 3.75 lbs Pilsner 2 row
- 2 lbs Vienna
- 1.75 Munich
- 1.5 Caramel (40L)
- 14 oz Aromatic

Mash temp 150.

1.5 oz Tettnang
1 pkg of White Labs German Ale/Kolsch

 

[Calder]

10 lbs of grain. Assuming you hit the final volume, the difference in gravity is a result of your mash efficiency. 1.045 in 5 gallons (final volume) would be about 60% efficiency. 1.054 in 5 gallons would be about 75%.

75% is more 'normal', but it all depends on your process. Many people get 80%+.

Why did it go so low? 1.045 to 1.008 is greater than 80% attenuation (37x100/45). That's pretty good. Attenuation has many variables, so it is difficult to really know what you will get. Only when you have a consistent process and you know the yeast can you really confidently predict the attenuation. I suspect your high attenuation was driven primarily by your mash temperature. You say you mashed at 150 F; the lower the temperature the more fermentable the sugars = lower FG.

Adding DME would have increased the OG and the FG. Probably of the order of +.001 to the FG for every .004 added to the OG. for example, 1 lb of DME in 5 gallons will increase the OG by .009. It is approximatly 75% fermentable, so the FG would have increased by .002. Even if the beer has finished fermenting, you can still do this if you want. Boil the DME in a small amount of water for a few minutes, cool and add to wort/beer; minimize aeration, as the yeast do not need it at this stage.

 

[zirb]

Thanks. Very helpful.