Pitching billions of healthy yeast cells into your wort reduces lag phases, off-flavors, and risk of infection. Your beer will thank you!
Goals when making a yeast starter
- Increase cell count. Having a high pitching rate makes better beer.
- Increase cell viability. Healthy yeast cells ferment quickly, produce minimal fermentation byproducts, attenuate fully (ferment to a proper final gravity), can ferment high-gravity worts, and have more tolerance for high concentrations of alcohol.
- Reach full attenuation. An insufficient amount of cells may ferment sluggishly or incompletely, especially in a high-gravity or lager wort.
- Shorten lag and growth/respiration phases. Reducing the duration of the lag and growth phases minimizes the opportunity for wort contamination and the formation of fermentation byproducts.
- Improve beer flavor and aroma. Underpitching creates stress - too much work for too few cells. Stressed cells are more likely to create off-flavors or aromas in the finished beer.
Brewer's yeast (Saccharomyces cerevisiae and S. carlsbergensis) is a single-cellular fungus that consumes simple sugars in the wort and converts them to alcohol and carbon dioxide. There is always a delay between when yeast is pitched into wort and active fermentation. There is a direct correlation between the duration of the lag and growth phases and the number of cells that are pitched - the more cells, the less reproduction needs to occur and the faster fermentation begins.
Theoretically, you could pitch just one yeast cell into a fermenter full of wort and the cell would keep dividing until there were enough cells present to ferment the beer. Given enough cells, brewer's yeast will outcompete other microbes and quickly provide the desired fermentation.