Yeast Starters
Hitting the right pitch rate, and the science of growing yeast
Pitching rate (how many yeast cells you add to your wort) affects flavor, fermentation speed, and attenuation. Underpitch and you get more esters and fusel alcohols (sometimes that's what you want in a Belgian, usually not in a lager). Overpitch and you lose yeast character. The starter calculator helps you hit the right number.
In the recipe builder, the yeast section shows whether you need a starter based on your OG, batch size, and yeast package date. If you do, it calculates the starter volume and DME needed, with support for multi-step starters when a single step isn't enough.
Pitching Rate
Rate = 0.75 M cells/mL/°P for ales, 1.0–1.5 for lagers. V = batch volume in liters. °P = degrees Plato from OG.
Viability
Yeast cells die during storage at about 0.7% per day. A 3-month-old liquid pack might be at ~40% viability. That's why starters exist. We calculate available cells from your package type, count, and manufacture date.
Two Growth Models
White Model polynomial growth
Based on White Labs yeast growth data. Growth depends on inoculation rate. At lower cell densities, each cell has more nutrients and reproduces more. Aeration adds +0.5 to the growth factor. This is the more sophisticated model and what most starter calculators use.
Braukaiser Model linear growth
Simpler: each gram of DME produces about 1.4 billion new cells, regardless of starting density. Based on Kai Troester's cell-counting experiments. Works well for typical 1–2L starters and is easier to reason about.
Where This Comes From
The White model polynomial comes directly from Yeast: The Practical Guide to Beer Fermentation (2010). The Braukaiser model comes from Kai Troester's documented cell-counting experiments. Viability decay rates are from White Labs packaging data. Package cell counts come from manufacturer spec sheets.
Sources
- White, C. & Zainasheff, J. Yeast. Brewers Publications, 2010.
- Troester, K. “Yeast Starter.” braukaiser.com.
See all the numbers come together in real time.
See this in the recipe builder