How To Create A Yeast Infection

Brewing your own beer, as I'm beginning to discover, can be fun and rewarding. It can also be expensive. The grains to make a two gallon batch, as I do, can cost around ten bucks, but the yeast, which is most often packaged for larger batches, gets expensive. The dry yeasts are only about $1.50, but the liquid packs made by Wyeast, available in numerous varieties, cost around $6.50. To save some money and have some fun, I wanted to culture the yeast for future use. Benefits of yeast culturing include reduced costs, fun, and a steady supply of long-lasting yeast for your beer brewing whims. Downsides include extra work (if you can call it that) and reduced strain diversity. With culturing, unless you have a huge operation, you're basically stuck with the same strain. According to Wyeast and the homebrewing literature, the different strains of yeast can produce vastly different beer styles. I don't know nearly enough about either the biochemistry or mythology of yeast to get into this in any detail.

If there's anything living yeast (and most other life-forms) love, it's reproducing. Culturing yeast is essentially the process of promoting long, slow reproduction. Then, once you're ready to make beer, the yeast will be ready to reproduce rapidly.

Begin by collecting lab equipment. Lab glass and rubber can be subjected to high heat which is essential to the process. I use American Science and Surplus for my lab needs. I got an Erlenmeyer flask for mixing and 10 test tubes with rubber caps. Here's the process I used to make the gelatin cultures. Sterilize them by steaming for about 15 minutes. Okay, this doesn't sterilize it, but I don't feel like using a pressure cooker or autoclave. It should be sufficiently germ-free for safe culturing. If it's not, it'll be obvious. My steamer setup is a shallow pot with a steamer basket and a lid. Very basic.



Make a starter wort with water and about 10% dehydrated malt extract. Bring it up to a boil, add gelatin, and whisk to combine. This is the growing medium and will provide a growth surface for the yeast and enough food to nourish the yeast for a long time.

When the test tubes are cool enough to handle and the gelatinized wort has cooled a bit but not yet set, fill the tubes with the wort 1/3 - 1/2 full, reserving one empty tube. Lay them down at a narrow angle so that the gelatin sets slanted.



For this process to work properly, it helps to brew a batch of beer today or tomorrow. This works best with liquid yeast like the Wyeast varieties. Activate the yeast by slapping the pouch. It doesn't seem that weird if you've seen the pouches. If you have the wort ready for a batch of beer today, you can add the yeast to it when the cultures are all done. If not, make a starter wort of about 300ml water and 1.5 oz malt extract powder. Pour some of the activated liquid yeast into the empty test tube and the rest into the starter wort. Cover the starter wort with foil (or a proper stopper with an airlock) and add it to the beer as directed in the Porter post. Here's the starter that I used in said Porter:



Unless you have a proper inoculating loop, you have to MacGyver one. I used a straight pin stuck through a drinking straw. Sanitize the straw and pin with rubbing alcohol or whatever you have handy. Dip the pin into the yeast in the separate test tube. The tip of the straw should collect a little bit of yeast, which will help the culture develop quickly and effectively. Deposit the yeast on the gelatin and gently pierce the gelatin with the pin. This will allow the yeast to take a good hold and access the food contained within the gelatin. Cap the test tubes and set aside.

Good yeast will begin reproducing and spreading right away. A white film on the surface is a good sign. Anything colorful or fuzzy is a bad sign. Once the film is pretty solid, put the yeast tubes into the fridge where they, I'm told, will last 3-6 months. Hopefully in two-ish weeks I'll be able to put the yeast cultures to the test with my next batch of beer, an ESB. Here's the yeast after one week. Notice the white film and lack of fuzz. The instructions say to use electrician's tape to seal up the tops so I did (after taking this picture).



Prost!