First, to do this: You MUST be extremely anal about sanitation
. I do not say this to be a snob or say 'I am better then you'. We are dealing with unhopped, raw yeast. The chances for infection are EXTREMELY HIGH. That said, RELAX, don't worry, even I can culture yeast!
Second: The beers I like, I REALLY LIKE
. I want to reproduce them like the commercial breweries, or as close as I can get. In order to do that I need repeatable methods and exact measures. This method provided me a quick and pretty simple means to a repetative process w/o having to invest in a micro-biology lab.
I tried to follow Papazian's yeast culturing from The Complete Joy of Homebrewing. His process though seemed to be a complicated way of making a starter, I missed something along the way. So, my method is based on the method outlined by Charlie, and is basically exactly like making a really small batch of beer except for a few minor things (that are very important) :
don't require hops or grains; wort CAN be substituted
bottles must be stored in fridge afterwards
you want the yeast sediment in your bottles
I got a couple dozen pint bottles for starters on clearance at a supermarket; I also have a half-gallon growler I saved from a pub and it serves as a nice, small primary. I bought a bung to fit it, and just use that.
If you only ever want to use 1 type of yeast, then it is even simpler because you don't have to bother with lots of different strains.
8 pint 'starter' bottles
1 - 1 gallon carboy, jug, etc. to serve as a Fermenter
1 - bung to fit
1 - airlock
1 lb. DME
1 gallon of H2O
1 Yeast strain to harvest (White Labs vial, Smack pack, etc.)
~1 cup corn sugar for priming
Boil up 500 grams (1lb) of dry malt extract in 4 litres (1 US gallon) of water. Light pale malt I have found works best, that way you're not imparting off-flavors from your starter.
Dump it into a 1 gallon fermenter (that is extremely well sanitized), put on a fermentation lock (an S-type with little liquid so it won't suck back as the wort cools), and allow to cool to pitching temperature. This will take about 3 hours.
While the wort is boiling, fill the sink up with ice water. Chill your wort to pitching temperature in the sink. (While it is in the pot, NOT the glass fermenter. DO NOT chill hot glass in the sink, YOU HAVE BEEN WARNED) Dump it into a 1 gallon fermenter (that is extremely well sanitized), put on a fermentation lock.
At this point it is best to allow your break material to settle out, ~20mins, then carefully pour your wort off the sediment, leaving it behind. If you don't do this extra step, you'll be encouraging your yeast to spoil faster (although it will still last a long time).
I make a Pale Ale every 2-4 months for my friend and Dad so I simply make up an extra amount of beer wort when I brew it, prior to adding aroma hop additions, I draw off the extra gallon. You could do this with ANY wort though, best to use a lighter concoction, but dark is fine, too. Just draw off your gallon in a sanitary fashion, then use it instead of the specially prepared wort. Of course, this means that your yeast in question won't be able to be used for that brew.
Now, with your wort (minus trub sediment) in your 1 gallon fermenter, take your swollen yeast package and pitch it into the fermenter.
Aerate the wort well either by shaking, or with an air pump. Let this ferment until it is done, then bottle it.
However, before you bottle, you have to give the jug a really good shake to get all the sediment mixed into the beer again. This shaking has to be done extremely slowly and carefully so as to not cause a geiser. Little by little shake to release CO2. Eventually you'll be able to give it a good swirl to mix in all the sediment, without having it foam over. Afterall, the whole exercise is for propagating yeast, and most of that sediment is yeast.
This is the only time I actually bottle prime beer - I use about 3/4 tsp of corn sugar for each bottle.
Fill each pint bottle about 2/3 full of wort, this ends up being just short of 2 cups per bottle.
Note as well that you really have to soak your bottles well in your sanitziing solution, and make extra sure that all your equipment is well sanitized. Also note that you can just pour the stuff from the gallon jug through a well- sanitized funnel into the bottles. I don't bother with a siphon as the yeast will gladly eat up any oxygen that gets in this way. Just be careful to clean the mouth of the jug well beforehand with some high-octane (80%) vodka or something, and possibly flame it with a lighter, too.
Now you have 8 "clones" of your original yeast strain. These need to be stored in the fridge, so make sure you have plenty of room. I also label the bottle with the date and the generation. I have been told to start over at 8 or 9, but I haven't got there yet, I am at 3 on Cali Ale strain. This can get exponentially out of hand, if you make 8 then 8 from those 8 you have 64 pints. I just make sure to plan Yeast Ranching when I see I only have 1 pint left of a particular strain. The day before brewing I make the gallon, bottle 7, and the 1 left over go right into making a starter.
1 pint bottle of yeast, from above ^
.5 cup LME
2 cups water
Half gallon or so fermenter.
Boil the water and malt for 10 mins, cool in sink right away.
Poor off the liquid from the pint til JUST before solids want to drop in. You can poor this in a glass and drink the lightest beer EVER. I don't 'enjoy' this beer, but I do taste it to make sure that it's not sour, metallic, infected.
Swirl the sediment into suspension
Pour wort and swirled yeast into fermenter.
Swirl ever 1-3 hours
Ready to pitch when bubbling every 10 sec's. (8-9 hours for me) Your milage may probably will vary. I imagine after a couple you will get a feel for how long this takes, and can plan a little ahead on brew day.
Hope this helps!
The Complete Joy of Homebrewing, Charlie Papazian
Bodensatz Brewing, www.urbanhippy.ca
All the St. Louis, Dayton and Cinci brewers that put up with my needling