yeast ranching for the Junior Scientist in all of us
Yeast culturing is cool because it's where you get to pretend to be a microbiologist, use neat gear, and save about a ton of money on liquid yeast.
Yeast cultures can be done in slants (ie, test tubes leaned so the media congeals at an angle or "slant"), in petri dishes, or frozen in specially prepared anti-icing media. I use the slant method.
Yeast culturing is not particularly difficult but it does require a bit of time, some extra pieces of hardware and sterilization (not sanitation) that you don't often use in homebrewing. Planning ahead can greatly reduce the time factor.
Basically you make some media for the yeast to live on, inoculate the media with the yeast, then later on you inoculate your starter with the cultured yeast and pitch when ready.
gear
bulk lot of 100 borosilicate test tubes off eBay - $10. You probably don't need that many but they were cheap.
There are many fine pages on the net that describe the inoculation process, so I will instead talk about the overall workflow.
The week before: slant prep
Create the slant media. I usually make 10 slants from each culture. One cup of media is overkill for this, but it allows for mass spillage and other disasters.
Stand up your tunes. I use a cheap tube stand.
Heat 250ml of water. Add 15g of DME and stir until dissolved. Remove from heat. Stir in 5g of agar powder and stir until dissolved. This is the agar media.
Pour/inject/turkeybaster/whatever a bit of the media into each tube. I have never measured the amount, but it would likely be something like 10-15% the capacity of the tube. If you have too little media the slant will be so thin and low in the tube it will be hard to work with. If you have too much the media will take up too much room and it will be hard lean it far enough to get the slant shape without the media running way up the side of the tube.
Stuff a cotton ball in the mouth of each tube. You can also use foil/stopper/whatever, but I am currently working with cotton to minimize water vapor.
load the slants in the container into your pressure cooker and cook for 15mins at 15psi. Allow to cool overnight. By morning the slants will be cool, set in their slanty position, and hermetically sealed with their cotton balls still in place. Note: while you've got the cooker going you might as throw in a mason jar of water (for quenching the loop, below) and one or more jars of wort to use in making starters. Having sterile starter around is a huge encouragement to making starters for your yeasties.
Allow the tubes to evaporate excess water droplets; this is why we started a week in advance instead of a day in advance. The slants shouldn't stay cotton-balled for a long time or the media will dry out. Letting them dry at a downward angle will encourage water droplets to roll down into the cotton and wick away instead of into the agar.
Day of: The actual inoculation (under construction)
cultural history
Culture-al history, hahaha!
culture[6]: 20080705 - inoculation of slants from White Labs WLP005 British Ale yeast. 5 slants, SITC method.
culture[5]: 20080606 - inoculation of slants from Wyeast 1056 American ale yeast. 10 slants, SITC method.
culture[4]: 20080515 - inoculation of slants from a buddy's White Labs WLP720 Sweet mead yeast. 1 slant, SITC method.
culture[3]: 20080504 - inoculation of slants from Wyeast 3068 Weihenstephan Weizen yeast. 10 slants, SIT method.
culture[2]: 20080501 - inoculation of slants from Wyeast 1098 British Ale yeast. 10 slants, HAP method.
culture[1]: 200r870425 - inoculation of slants from Wyeast 1275 Thames Valley Ale yeast. 12 slants, SIT method. Taped and refrigerated after 4 days growth.
culture[0]: failed attempt to culture yeast from a Sierra Nevada bottle.
some methods I am testing
The main problem I am experiencing is water condensation (presumably from the agar) in the tubes.
From best to worse so far:
SITC=Sterilized In Tube: agar poured into tubes, tops stuffed with cotton ball. Pressure cooked 15psi/15min with "canned" stoppers, cooled in closed cooker overnight. Note: pulling the cotton out results in wispy attachments. Twisting the cotton before removal greatly reduces this problem.
HAP=Hot Agar Pour: agar and tubes sterilized 15psi/15min, agar cooled somewhat, poured into tubes and cooled.
SIT=Sterilized In Tube: agar poured into tubes, loosely capped. Pressure cooked 15psi/15min, cooled in closed cooker overnight..
SIOT=Sterilized In Open Tube: agar poured into open tubes, caps separate in pressure cooker. Pressure cooked 15psi/15min, cooled closed cooker overnight. Caps placed on when cool.
the mousepad
Yeast culturing is cool because it's where you get to pretend to be a microbiologist, use neat gear, and save about a ton of money on liquid yeast.
