If you do it at 80%, the yeast will finish the sugars and be active to reduce the VDKs. The increased activity will help scrub off sulfur. Then you can crash down to cold temps to lager and drop out the haze and yeast. The classic profile has a slow cooling to keep the yeast working, as they will slowly reduce the VDKs at low temperature.good info from everyone. seems like we are all on the same page. it just seemed odd to me to hear people do a d-rest after 2 weeks at 50F...seems all activity would be done and there would be nothing gained from doing a d-rest then (considering a normal lager range around 1.050-055). maybe for bigger beers over 1.060 there would still be fermentation activity near the 2 week mark - i just haven't done a lager that big.
As long as you don't remove the yeast from the beer, it doesn't matter if all activity has ended. Warming the beer for the d rest will make it active again.
ok good to know. but then whats the difference in doing a d-rest at 80-85% attenuation , vs. 99-100% attenuation ? any benefit of one over the other
So you clean it up, blow off sulfur and save time. If you are a homebrewer that brews lagers when the weather allows, saving time in the fermenter is a good thing. Might have to get another freezer someday so I can do lagers in the summer.