Yeast Slants pt 2

Well, I did a test inoculation of a couple slants and a petri dish with some yeast from the bottom of a bottle of a commercial Rogue beer and realized pretty quickly that my first batch of agar/wort mix was not going to work. I had put way too much agar in the mix and it was so thick that I couldn’t even get my inoculation needle to scrape the surface. So, I cleaned out all the petri dishes and slant vials and remade a new batch of wort/agar following the process in the previous post, and this time I used 7 grams of agar for 500 ml of wort. The results were much better, I ended up with a much more usable substrate to grow some yeasties on.  Here’s what the new batch looks like:


Since I recently picked up a new vial of White Labs WLP002 English ale yeast for a special bitter I’m brewing this weekend, I decided to try inoculating a few of the vials with the yeast.

I fired up my home made alcohol lamp to sterilize the inoculation loop, and rested the loop in a jar of Starsan and water.  I ran the loop thru the flame a couple times, dipped it in the yeast and then quickly jabbed it into the wort/agar mix in one of the vials a few times and then capped the vial. I repeated this for all 5 vials, the whole process only took a couple minutes.  About 3-4 days later this is what the vials look like:

The white stuff growing on the surface is yeast that has colonized the agar. The vial on the far right, however, has been infected by something and is growing mold. The mold is the bluish, fuzzy spot about a 1/3 of the way up from the bottom. Here’s a closer look:

This vial will not be kept since the mold will soon take over the surface of the agar.

After a few more days the non-infected vials should have yeast covering most of the agar surface, and at that point I’ll label the vials and store them in the refrigerator.  I wrapped black tape around the cap too, to make the vial air tight. They should be good for 6 – 12 months, and if they start to get old I can always re-slant them in a fresh vial.

On the 16th I brewed a batch of American Wheat beer  and before pitching some washed WLP001 California Ale yeast I streaked a petri dish with yeast using the same basic method shown above. After a couple days it had yeast colonizing on the dish, so I scraped some yeast from the dish and inoculated 3 vials with WLP001. My yeast library now has 2 strains!

In the future I’ll document the process of stepping up the yeast colony to a size that can be used in a batch of beer.  I plan to use a pipette to add about 10 ml of sterile wort into the vial, letting the yeast multiply for a day, and then shake and add the wort/yeast mix into the 8oz mason jelly jar of sterile wort with a stir bar and let the yeast grow more while it mixes on a stir plate for a day. The final step will be to pitch the yeast mix into a 1000-1500 ml wort mix in a flask on a stir plate overnight before adding to a batch of beer on brew day.

Ain’t science fun?!?!


Posted on July 19, 2011, in Yeast Propagation. Bookmark the permalink. Leave a comment.

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