Although these two subjects have been addressed many times, there are some aspects that seems to have been missed. I realize that there are many opinions on whether or not a diacetyl rest should be done in the first place, but I don't want to get into that debate in this thread. I just want to be clear on what the recommended process for doing a diacetyl rest is, if one were to decide to do one. In his book Yeast, Chris White suggests that a diacetyl rest should be done when the lager is 2-5 specific gravity points before reaching terminal gravity. The temperature of the lager should then raised into the 65-68 F range for a two day period. He then suggests that the temperature of the beer should be lowered to encourage flocculation of any remaining yeast. He then discusses whether the beer should be crashed to lagering temperatures or whether the temperature should be lowered slowly. He answers by saying that below 40 F, very little happens. Thus once you reach 40 F you can crash it to the desired cold conditioning temperature at or near freezing temperature. He also says that if you want the yeast to be active and carry on reduction of fermentation by-products, it happens much faster at higher temperatures. He says, however, that very rapid reduction in temperature (less than 6 hours) at the end of fermentation can cause the yeast to excrete more ester compounds instead of retaining them. Also, if you plan on repitching the yeast, you should avoid very rapid temperature changes. He says that after fermentation slows and the yeast begins to flocculate, the brewer should start to slowly cool his beer at a rate of 1-2 F (0.5-1 C) per day in order to avoid sending the yeast into dormancy. "After a few days", the beer has reached a temperature close to 40F (4 C) but there are still some fermentable sugars remaining. The brewer then transfers the beer into the lagering container (e.g. keg). He says the yeast needs to remain active for a long time in order to reduce any fermentation by-products. He therefore leaves one guessing how long the beer should remain at 40 F before crashing to cold conditioning temperature. Having read all this, I realized that he didn't explain his process very thoroughly, and left a lot of questions unanswered. Here are some of the questions I had: 1. When you raise the temperature near the end of fermentation to 65-68 F (I assume by taking the keg out of the kegerator and placing it directly in a room at that temperature), wouldn't that rapid increase in temperature over such a short period of time (perhaps a day?) result in the shocking of the yeast? 2. Once you have completed the two day diacetyl rest, you then bring it back down to the initial fermentation temperature and slowly reduce the temperature by 1-2 F per day until "after a few days" it reaches 40 F (this implies that the beer was initially already at the fermentation temperature (e.g. approx. 47-55 F). Chris White failed to mention whether this slow reduction in temperature also applies to bringing it down from 65-68 F to the initial fermentation temperature. His logic would seem to apply, although at 50 F fermentation temperature, it would take about 8-16 days, and an additional 5-10 days to get it to 40 F. A total of 13-26 days!!! So does Chris mean to crash it down to fermentation temperature (wouldn't that shock the yeast?), or to lower it gradually a degree or two a day? 3. Chris White says that the yeast are still active at 40F and need to remain active "for a long time". So, how long does he suggest that the beer should remain at 40 F before crashing to cold conditioning temperature? With what he seems to imply, I can see it taking a month or more after fermentation is almost finished before it can even be cold-conditioned. I would be most appreciative of any comments or suggestions. (P.S. I did write to White Labs concerning these questions, but did not get a reply).