I began this current project with a few simple questions – how many bugs are flying around my lab? Is my work area really as “clean” as it looks? And, how likely is it that any batch of beer is going to be infected by a bug (bacteria, wild yeast, etc.)?
FIRST THINGS FIRST
As most projects go, I started by researching the subject. I read and reread Yeast, watched several YouTube videos on how to culture yeast, and read many blogs and articles on the process of yeast ranching. Taking some of the yeast (Lallemand Nottingham Ale) from a current fermenting beer, I began my journey as a yeast rancher.
I have yet to read anyone who says culturing dry yeast is worth it, but I think losing $3.99 is better than $6.99. So, this was my test batch to see whether I could keep the area clean and sanitary while culturing the yeast. I began by putting everything that could fit into my stove-top autoclave. Spend some money and get a good autoclave rather than a pressure cooker. If you are going to herd yeast, this is one piece of equipment that you must have. Be sure to follow the instructions. You’ll want to purge the autoclave of air and allow pressure to build up to around 17 -20 psi (about 235-240 F) to sterilize your glassware and agar.
The next step requires that you pay attention to your surroundings. There are many formulas for agar, all sharing the same ingredients: agar, DME, and yeast nutrients. Boil the DME and nutrients, then add the agar. Pour into either a culture tube or petri dish. The amount of agar in the petri dish need not be very thick. The culture tube should have a little less than half the total volume available (if the tube is 30ml, then you need a little less than 15ml). Place everything into the autoclave and sterilize for at least 35 minutes.
After the glassware is touchable, remove everything from the autoclave. While the dish is warm, but the agar is set, turn the dish upside down and let cool for several days, or until the condensed water is gone. Take some Parafilm and wrap the petri dish if you do not intend to inoculate immediately. The culture tubes are a bit different. Remove them while the agar is still liquid and place them on a 30 degree angle (thus the name slants). Be sure the screw cap is semi-loose while the agar is setting up. As with the plate, allow enough time for the condensation to dry. Parafilm when ready.
WORDS OF CAUTION
If you take away anything from this blog, remember to make sure that everything you touch – that will in any way come into contact with anything from this point on – is sanitized and/or sterilized. Remember, you want your laboratory to be as clean as possible; free from draft, dirt, and anything that will contaminate your yeast. If you think your area is clean, it isn’t. If you are of the mindset that there is absolutely no way mold or bacteria can get into your culture, you are imagining things. Unless you have a cleanroom (as in a commercial laboratory), you’ll have to take every precaution you have heard or read about to even have the slightest hope of culturing yeast that carry zero contaminants.
Getting back to inoculating your dishes and slants.
Make sure you have a Bunsen burner, inoculating loop, nitrite gloves, and alcohol (look below for a complete list of necessary equipment). Before you attempt to inoculate your plate or slant, you should practice holding two tubes with one hand, know where you will put the cap, and practice taking a sample from one tube and placing the inoculating loop into the other. There are many great articles written by experts showing how this should be done.
I used to pride myself on keeping my lab clean, making sure no bugs would enter my beer. Oh, was I ever in for a rude awaking.