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First Bock - FG question

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MNcoldbreak

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Does it sound like I am good or should I add some more yeast?

I have been brewing for about a year. I finally got a 5 cu ft freezer chest (nicely fits a 6.5 gallon carboy or 2 kegs and a 5 lb CO2 tank) so decided to try a lager.

I am making a traditional bock with an estimated OG of 1.066 and an estimated FG of 1.017 for a 5 gallon batch.

My actual measured OG was 1.061 and just transferred to my lager vessel at a corrected gravity of 1.017 (using a refractometer). Since my OG was 5 points lower should I assume my FG should also be 5 points lower considering no change in yeast attenuation? If so, would it be a bad idea to add another packet of yeast now? I would think if I did this I would have to again transfer it before a two month lager exposing it to more oxygen and possible contamination which sounds like a bad idea...


I used Wyeast 2206 Bavarian Lager and followed beersmith recommendation for a stepped starter with a 1 liter and then 2 liter starter.

I fermented 2 weeks at 50 degrees until I was at a corrected gravity of 1.020 and then did 3 days at 60 degrees for diacetyl rest (No butter taste so probably didn't need it). After the D rest I was at 1.017. I then dropped to lager temperature over 5 days and am still at 1.017. The bock is perhaps slightly sweet, but I may be bias because I tasted it after seeing the gravity reading.
 

rburrelli

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Leave it alone. Not correct to assume you would be 5 points lower in final gravity. It does not work in a linear relationship like that. Yeast is a living thing and will do what it does. I see no need for additional yeast and think you are correct about your sweetness bias.
 

VikeMan

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My actual measured OG was 1.061 and just transferred to my lager vessel at a corrected gravity of 1.017 (using a refractometer). Since my OG was 5 points lower should I assume my FG should also be 5 points lower considering no change in yeast attenuation? If so, would it be a bad idea to add another packet of yeast now? I would think if I did this I would have to again transfer it before a two month lager exposing it to more oxygen and possible contamination which sounds like a bad idea...


I used Wyeast 2206 Bavarian Lager and followed beersmith recommendation for a stepped starter with a 1 liter and then 2 liter starter.
Let's assume that 1.017 was a good estimated FG target for the recipe's OG of 1.066. That's:
(1.066 - 1.017) / (1.066 - 1) = 74.2% Apparent Attenuation

All else being equal, 74.2% Apparent Attenuation for your actual OG of 1.061 would give:
((1.061 - 1) x (1 - .742)) + 1 = 1.016 Estimated FG

(This all assumes that the original FG prediction was reasonable for the grain bill, mash temp and length, and yeast strain. Most software doesn't take the makeup of grain bill into account when prediction attenuation/FG.)
 
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