Stepping Up Your Starter
TroubleShooting
Tom Bechard • Rouses Point, New York asks,
I have been all-grain brewing for about six years. I usually did 10-gallon batches but started deliberately making 11-gallon batches and canning the extra gallon of wort in one-quart mason jars. I use the unfermented wort to make liquid yeast starters. This way I can honestly say that my entire brewing process is all-grain.
Because the object of making starters is to grow more yeast, how big an increase in starter volume is required to grow more yeast? It seems that too small an increase in starter volume will only feed the yeast cells already there with no increase in cell population. The cells that are there will just eat the new wort and that will be that.
I usually use a factor of 10. If the initial package contains 50 milliliters of starter, I pitch it to a 500 milliliter starter. If I step it up again it will be to 5,000 milliliters of starter. Is this the best way?
The approach you use is the conventional method used to grow yeast in commercial breweries of all sizes. The notion that feeding a yeast slurry with a small volume of wort does not lead to an increase in cell population is indeed correct. In fact most cell suspensions grown under laboratory conditions have a maximum cell density related to the environment in which the culture is grown.
In growing yeast, the oxygen content, specific gravity, and nutritional quality of the wort along with the propagation temperature will affect the maximum cell density of the culture. To keep the population growing the volume must increase. As a rule of thumb increase your propagation volume by a factor of five to 10, making the larger increases occur early and progressively drop as the total volume approaches that required for pitching.
One problem with propagating yeast that bothers many homebrewers is the dilution of the recipe’s wort with the propagation wort. The best way to minimize this problem is to allow the last step of your propagation to complete its fermentation and the cells to flocculate (clump and sink). Then you pitch the bottom of the starter. This not only concentrates the yeast cells to a much smaller volume, typically about 5 percent to 10 percent of the propagation volume, but it also selects for flocculent cells from a potential mixture of flocculent and non-flocculent cells.
Many brewers want to know the secret of great beer. In my opinion great beer can only be made time after time if the basics of yeast are understood. The key to yeast is to have it clean, alive, and in sufficient quantity to take off quickly. Your approach to handling is a great start to guaranteeing success with yeast.
