Lager Temperature

After fermentation, when I raise temp for diacetyl rest and then bring it back down for lagering what is the recommended rate of increase / decrease per day ?

I plan on setting my thermostat at 9C (48F) with hysteresis set to 3C.
In other words temp will vary between 9C and 12C - is that OK - can I go lower ? Say, 8C - 11C ?
(Bohemian and Munich yeast)

Get it down to 0c to 3c if you can. Makes for a smoother lager.

The 8C to 11C will be for fermenting. I will be sure to lager lower.
What would you say is a safe temp adjustment rate ?

Boet, ferment the lager at 10C or so until the lager is completely done, ie after your diacetyl rest if you do one, then when you're absolutely sure it's done, just crash cool it to 0 or so and lager. You don't need to slow it down at all.

Check out Kaiser's site for a wealth of info.

Thanks mate.
If the temp is raised or lowered too quickly I thought the yeast gets stressed. Is there no rule of thumb - like 1C per day?
In other words - lager at 10C then raise temp 1C per day to 17C for four days then reduce at 1C per day to lagering temps ?

Well crash cooling the beer will just put the yeast into a dormant state, not stress it. This isn't a problem if your fermentation is completely finished, and all diacetyl and acetaldehyde etc have been reduced.

Quickly raising it while the ferment is underway is a completely different kettle of fish, although in the case of a diacetyl rest, afaik you need it to come up fairly quickly - perhaps over the course of a day at most. You should do the diacetyl rest when the the gravity has dropped about 75% of what you'd expect, so that the yeast is still very active. If you wait too long and the beer ferments out, then the yeast may not do a good job of reducing the diacetyl.

There is another school of thought that says that if you pitch cold, (7C or so) and slowly ramp up to 10C over the course of a day or two, that very little diacetyl will be produced and a diacetyl rest is actually unnecessary unless your strain is a notable diacetyl producer. You definitely need to do one if you pitched warm and let it cool to 10C overnight, for example, as some people do.

Cool, thanks.
Nice avatar ! You must be missing the weather ?

Thanks! You have no idea, it's so depressing here!! Thankfully I'm only here for a few years (I keep telling myself that), and I'll be home in feb for a holiday, sun sea and surf here I come!

There is one effect that crash cooling a lager may have and Kaiser and I have discussed this before. In Brewing Science & Practice, Briggs states that slowly cooling (e.g., 3 - 5°F/day) a lager is essential because crash cooling may cause the yeast to excrete proteolytic enzymes, which would reduce foam/stability. Many homebrewers still crash cool lagers with no noticeable effects, but that is the scientific thinking behind it, so one does it at their own risk.

I believe the late Greg Noonan (New Brewing Lager Beer) also stated not to crash cool lagers. However, I don't believe he got into why. I have not seen any brewing literature that states it is OK to crash cool a lager with an explanation as to why it is OK. I've only seen the opposite.