So I am going to try to krausen my Sam Adams Boston lager clone in order to achieve 2 things: (1) carbonation in the bottle; (2) some removal of possible diacetyl. I've heard that one must raise the volume by 3 gravity points before bottling in order to create adequate carbonation without using priming sugar.
So I will brew a typical 5.5 gal batch and remove about 1/6th of the postboil volume (say 0.75 gal) to freeze. I'll do the same with the yeast starter (except it goes in the refrigerator). I plan to take volume and SG readings once the lager has been through secondary fermentation and is ready to bottle. I'll then take my saved wort and yeast, get them to room temp, pitch the yeast, and let it ferment to an SG that, once added to my beer, will raise its gravity by 3 points. I will then bottle. Does this make sense? So suppose:
5.5 gal batch originally.
0.75 gal saved for the krausen, 4.75 gal left in primary.
4.5 gal left after secondary fermentation at 1.012 SG.
Ferment saved wort to 1.033 SG and pitch.
4.5 gal @ 1.012 SG + 0.75 gal @ 1.033 SG = 5.25 gal @ 1.015 SG.
This should ferment down to 1.012 or so.
Is 3 points adequate?