Pitching is the process of adding yeast to wort to start fermentation and produce beer. Whereas traditional winemaking still uses “wild” yeast on grape skins and in the winery environment to start fermentation, almost all types of beers are fermented by pitched yeasts.
The term “pitching” may seem to have connotations of a baseball throw, but it should actually be done gently so as to minimize stress on the yeast and ensure rapid growth.
Stored yeast is typically held chilled to minimize deterioration. Removing yeast from such cold hibernation and heating it rapidly may shock the cells and reduce the speed of fermentation, with undesirable results. Gentle treatment will allow yeast to initiate fermentation at the correct time and speed.
The number of yeast cells added per volume of wort is referred to as the “pitching rate.” Pitching rates may be expressed in terms of volume of yeast slurry per barrel of wort or as numbers of cells per milliliter. A typical pitching rate for warm-fermented ales would be 1 million cells/ml/degree Plato original gravity. Therefore, a 12°P wort might be pitched at 12 million cells/ml. This is only a guide and pitching rates will increase for strong beers to overcome the inhibition of high alcohol concentrations. Lager yeasts typically require higher pitching rates than do ale yeasts. Lower pitching rates are associated with slower starts to fermentations, higher rates of yeast reproduction, and greater ester production; the converse is true of higher pitching rates. Brewers determine, based on a number of factors, what pitching rate is best for each beer.
Some traditional yeasts have been repitched from previous batches, in succession, for decades and consistently produce the same character in the resulting beer. These yeasts have evolved a stable genetic composition and are a treasure to a brewer. More commonly yeast “drifts” with continual repitching and new cultures are required from the laboratory on a regular basis, typically every 12 or so generations, although some will refresh the yeast more frequently.
Pitching requires careful handling to avoid contaminating the wort. After yeast is cropped from a previous batch, it may be pitched into new wort in any variety of ways. It may be as simple as physically tossing buckets of yeast slurry into the fermenter or as complex as in-line dosing of yeast from brinks on weight load cells tied back to a computer—in this case the program delivers the exact weight of yeast desired. Oxygen may be added to pitching yeast to provide a building block for sterols to enhance growth, but oxygen is more often added to the wort.
Brewing Techniques. http://www.brewingtechniques.com/library/backissues/issue2.3/kingtable.html/ (accessed May 11, 2011). Edgerton, J. A primer on yeast propagation technique and procedures. MBAA Technical Quarterly 38 (2001): 167–75.
Brewing Techniques. http://www.brewingtechniques.com/library/backissues/issue2.3/kingtable.html/ (accessed May 11, 2011).
Edgerton, J. A primer on yeast propagation technique and procedures. MBAA Technical Quarterly 38 (2001): 167–75.