Yeast Culturing

I have a particular interest in home culturing yeast. While there exists a plethora of yeast strains at our fingertips in ready-to-pitch packages, growing yeast from my own stocks allows one more level of tinkering in the brewing process. After all, isn’t that what homebrewing is about? I have a collection of around 30 strains on hand, and while most of them are available from commercial suppliers, I do have a few that are not. One of my favorite strains is a mutated version of Wyeast 1338 from a commercial brewery. To me, that’s the kind of stuff that keeps this hobby interesting.

I have found plenty of both good and bad information on how to set up a home yeast bank. Personally, I think some people go a bit overboard and make the whole process too complicated. With about 15 years of microbiological experience, I thought it might be useful for me to pass on the simple methods I use. Home culturing is easy and fun.

A Word on Starters
Before I outline my method, here are my thoughts on starters based on practical laboratory experience. First, if you aren’t a clean person, just don’t try to culture your own yeast. Second, some people really over think this. Here’s what I mean. There is a lot of talk about doing step-starters by gradually increasing the volume of your starter 3- or 4-fold until you reach your desired final volume, but this is overkill. Typically I put about a half milliliter of my stock stock into about 5 mL of 1.040 wort. The yeast typically reach their maximum density in about 3 days. At this point I add the cells to 2 to 4 L 1.040 wort, depending on the size starter I need. The culture is placed on a stir plate, and continually stirred. There’s usually a lag for a day or so, but after that the culture really takes off. I’ve never had a problem with contamination, and my yeast are always greater than 95% viable.

I compared using my above method to the step-up method using Wyeast 1056. The cell density and viability from the single step method was greater than the step-up method (see details here). Both cultures were pitched in a split batch of a blonde ale, and the final beer was analyzed. In a triangle test I could taste no difference between the two beers. No need to make this more complicated than it needs to be.

The Yeast Bank Method
Here’s a simple method to making your own yeast banks. Don’t make glycerol stock and store them in the freezer, unless you have access to a -80C freezer. They won’t last very long, especially if they’re in an auto-defrost freezer. Plates and slants are a pain in the butt. Don’t waste your time with those; you need to continually reculture every month or so. If you have a somewhat large bank, this it way too time consuming.

Here’s the best way I’ve found to keep a yeast bank at home. Add cooled, sterile/boiled water to a test tube tube until it is almost full. I like the White Lab tubes, but any other small test tube (10-50 mL) will do. Pitch all of your yeast except for about a milliliter, and add that to the test tube. Put the cap on, and keep it in the fridge. That’s it. This will be stable for at least
a couple years. When you need to make a starter, shake up the tube and pour a half milliliter into 5 ml of 1.040 wort. Once that culture reaches maximum density, scale it up to your final starter volume.

I hope you find this method useful, and begin experimenting with home culturing.