Soon I will be brewing a Rogue Brutal Bitter clone. I have a three or four week old jar of yeast that I saved from the yeast cake from a previous brew (pacman). I also have an un-smacked smack pack of pacman yeast. Which should I use?
I’d use the slurry, no question about it.
The slurry should work well, if your sanitation is good. Or, if you want to be sure, you can order some chlorine dioxide capsules from Northern Brewer to clean the yeast of bacteria (but not wild yeast).
I always do a 5 gallon “starter” to grow yeast for big beers.
It deepens on the beer the slurry was from. If it was lower gravity beer that was not highly hoped, the yeast is still healthy and you’re confident in your sanitation. The slurry is the way to go.
Either way you should use a starter. 5 week old slurry very well could give you problems.
I’d use the slurry and just make a small “wake up” starter
THIS
I’ve been having better results by at least waking up any yeast slurry older than about 2 weeks.
??? Showin my noob colors here…I just racked over the beer that I currently had in my primary off it’s yeast cake into a secondary. Leaving primary alone with the entire yeast cake/krausen from the previous batch intact, resealed the primary and put it aside… Then boiled the wort for my Christmas ale, cold broke, and then poured the cooled wort directly into the primary with the old yeast cake ready to receive it’s new wort. My old batch of beer behaved as a starter for my new batch. Only thing is the OG of my current beer is 1.054 and the OG of my newbie beer is 1.084… I’ve been told to get ready for some massive blow off 
which I didn’t even think of… I just used a 5 gal bucket with airlock… guess I should have gone with a 6.5 gal glass carboy with blow off tube huh? Is my bucket going to explode? I’m turning my temp down now… rigourous bubbles comming from airlock. What do I do if the airlock gets all clogged up?
Sorry to post in this forum… I’m new here and didn’t know how to generate a new thread… In spite of Papazian’s repeated recommendation, I’m kinda worried here… :-\
Relax
Just put the fermenter somewhere that will make the mess easier to clean up when the havoc ends.
Leave the lid just on the bucket, dont bother snapping it tight, that way you wont have to worry about a clogged airlock.
My fermenter is in a thermostat controlled freezer… so if there is significant blow off, it will remain confined inside the freezer. Temp is now 63°F, which is well below the temp range for the yeast I’m using (WLP001 California Ale, optimum 68-73°F)… I guess when you’re pitching into an entire yeast cake, even though you’re well below the ideal temp, there is just so much yeast in the container, that fermentation will nontheless continue… Bubbling has died down, but has not stopped, and the airlock isn’t clogging up. Will too low a temp present any problems though?
+1.