The whole reusing yeast thing is blowing my mind and I don't quite understand the whole thing yet. I have an Irish Stout Brewer's Best kit in primary now. After it sets there for 4 weeks and I rack off the delicousness, can I scoop out some of the trub and use it on say...... an oatmeal stout? I'm still doing the extract kit thing because I'm newish (I do have the proper equipment for AG actually) and it's focking cold in Ohio right now.
If I can reuse this how much do I use? You said refrigerate until I'm ready to pitch, but I should bring it back up to pitching temp by leaving it on the counter for a couple hours or something right?
Nothing wrong with doing this provided you are happy with using the same strain of yeast for both the Irish stout and the oatmeal stout.
Refrigeration forces the yeast into cold shock...cold shock is a metabolic state in which metabolic processes are severely restricted, and hence, cold shock slows their reproduction time (length of time between budding events).
In the past, I have taken a 1 cup (using a kitchen measuring cup) scoop and put it into a vessel with 500-1000mL of fresh starter media, swirl it to resuspend the yeast...then just put it in the fridge with a loose cap/cover (so it can vent). Try to scoop from about the middle of the trub-depth to the top (I try not to get to the bottom of the carboy). Note that this is a general method I have used in the past...your long term method will have to be determined with trial and error, to get the correct population of cells in your starter for the next pitch.
NOTE: if you continually harvest your yeast in this manner, you can select for lower flocculating genetic strains (just a thought to keep in mind...but this should take many generations).
If you want to decrease the potential for contamination from the air, you can stuff sterile cotton (or part of a t-shirt) in the mouth of the carboy around the siphen hose...not perfect, but will help reduce the potential for contamination...this will make your siphoning slower if it is actually doing anything to filter the air. I did this a couple of times, then decided it wasn't worth the effort.
When you are ready to pitch, I generally let the yeast warm to pitching temp...but some pitch it cold. I personally think yeast should be at the correct fermentation temp before pitching - others would argue that it is not necessary. In my opinion, I want to pitch yeast that are happy, and healthy, but hungry...if they have to wake up out of cold shock, it will take them longer to get busy doing the business of replicating and fermenting (again, just my opinion).
Another method of harvesting your yeast (if it will be longer than a few days/1 week before you use it) is to collect around 100mL of your beer when you siphon it off, and add it to around 500mL of fresh starter media, then just stick it in the fridge. It will slowly grow over the storage time...if you don't think there is enough yeast to pitch by the time you are ready to use it, warm it up for a few hours (maybe as long as a day) before you start your next batch...again, this will take some trial and error to get it right.
There are a bunch of different methods of doing this...don't be afraid to try a few and determine which works best for you. The main idea is to keep the yeast alive by providing them some fresh nutrients for short term storage, and to keep them cold so they stay in cold-shock.
If you really want to reuse your yeast to cheapen up your beer...consider glycerol stocks if you have a freezer.
Hope this helps,
PikledBill
