Friday, March 13, 2009

Agar slants

Today I've decided to make some agar slants. The yeast that culturing is the Whitbread dry ale yeast, otherwise known as White Labs Dry English Ale yeast (WLP007) or Wyeast British Ale (1098). I made a few beers with this yeast and I was quite pleased. Made a great Brown Ale, Bitter, and hopefully a great Olde Ale. The Olde Ale is sitting in a secondary right now and the initial tasting on transfer was questionable. The good news is that it attenuated to almost 80% at 12% ABV!!!


See the equipment list here. Only additional equipment used is:

1) Test tubes with autoclavable screw on caps - these guys are great. Request the autoclavable caps.


1) Prepare the medium - I added 100ml of 10 brix wort to a flask with a pinch of yeast nutrient, a pinch of 5.2, and half a tablespoon of agar. I heated this in a double boiler type situation with for about 15 minutes to dissolve the agar.

2) Fill the test tubes - Using a small funnel and the test tube grabber, I poured each test tube about 2/3 full. Very loosely screw a cap on each.

3) Set up the pressure cooker - The instructions for mine call for 2.5 quarts of water, just enough to cover the cooking rack. Yours will likely be different. I placed a glass pyrex dish in the pressure cooker and the top half of a petri dish inside the pyrex dish, so that I could...

4) Lay the test tubes in the petri dish lid - The bottom of the tube goes inside the petri dish lid and the capped end rests on the edge of the petri dish lid. This way the test tubes are resting so that the culture medium will solidify in a slanted configuration when they cool.

4b) You'll also want to put some distilled water in a pyrex container of some sort and cover it with foil. Place it in the pressure cooker along with the test tubes (I put it next to the pyrex dish that the tubes are in, not in the dish). You'll use this to cool the flamed innoculating loop.

5) Process at 15lbs for 15 minutes - Follow the instructions for your particular pressure cooker.

6) Wait... It will take a few hours for the whole thing to come down to room temperature. Just before everything is cooled down and you're ready to innoculate...

7) Set up to innoculate the slants - Have your yeast, flame, and inoculating loop ready. I also wear a dust mask so I don't breath my filthy germs into my culture medium. This should be done in the cleanest, most draft-free area of your house.

8) Open the lid to the pressure cooker - Seal the caps on the slants. Note: At this point, if you notice that the medium in the slants has not congealed, you'll need to start over. You either boiled the medium for too long and denatured the agar, or you didn't dissolve the agar enough and didn't get enough into the test tube.

9) Get ready to innoculate - Put the test tubes in a test tube rack, and bring the rack and cooled container of distilled water over to your innoculating area.

10) Set up your flame. Quickly unscrew the cap from one of the test tubes.

11) Quickly flame the inoculating loop to sterilize it and cool it in the distilled water.

12) Quickly dip the sterilized inoculating loop in the yeast sample.

13) Quickly dip the innoculating loop into the test tube and streak the agar slant.

14) Quickly screw the lid back on the test tube.

15) Repeat steps 11-14 for each test tube.

16) Allow the yeast to culture up in the test tube at room temperature - You'll need to burp the test tubes periodically. Once or twice a day quickly unscrew the cap to release any pressure that has built up and screw it back on.

17) Once you've reached a point where the test tube no longer releases CO2 as you burp it, you can store the slants in the fridge. I put them in a ziplock bag and put the name of the yeast and the date on the bag.

Now I've got this yeast at the ready when I want to brew with it. Naturally, I need to culture this up to a full pitchable amount of yeast, which takes about a week and a half (10ml starters to 100ml to final 2 to 4 liter starter). Most literature says that a refrigerated agar slant will last about 6 months. So if you're not going to use the agar slant within six months, you'll need to culture it up to a small starter and innoculate a new slant. I'll probably use this yeast again within the next 6 months for a batch (or two or four) and when I start culturing it up, at the 10ml starter stage, I'll just innoculate another slant.

1 comment:

Slant Racks said...

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