Yeast is subject to 61 quality checkpoints during the production cycle and results are available through a Certificate of Laboratory Analysis report. Visit yeastman.com to view your results.
About the White Labs Process
Cultures are grown in small batches throughout a 17-day period to ensure the yeast is in optimal physiological condition for highest viability and multiple reuses. The cultures are propagated in all-grain wort produced in our custom brewhouse in San Diego, CA. Each culture undergoes a rigorous testing process from start to finish, which includes 61 quality checkpoints throughout the propagation cycle. Cultures are held following the completion of propagation and validated at the time of final quality control process, against all specification standards. Samples of each batch in final packaging are retained at White Labs to assist with research and development. Our tests adhere to the guidelines of the American Society of Brewing Chemists, when applicable.
Viable Cell Count
White Labs provides cell counts for every lot based on a spin down method (percent solids). We routinely validate the accuracy of this method through random manual cell counts. Our target cell count range is between 2.0 x10^9 - 2.8x10^9 cells/mL. Our cell counts may vary by strain so we provide a range as a reference.
Cell size variation by strain contributes to some strains having naturally more cells per volume than others. We have found our method to be accurate when predicting consistency of yeast performance during fermentation.
The manufacturing location of every package refers to where the cultures started their propagation cycles and were released from final quality checkpoints. In some cases, the yeast is produced in one location and packaged in another.
About the Testing Media
Lin’s Cupric Sulfate Medium (LCSM)
Utilizes cupric sulfate to inhibit the growth of brewers yeast and ensures no contamination of non-Saccharomyces wild yeast. LCSM is also capable of detecting S. diastaticus in brewers yeast cultures. If any growth is detected on these plates, further identification is performed as necessary, for example, to validate the presence or absence of S. diastaticus.
Hsu’s Lactobacillus and Pediococcus Medium (HLP)
Used to look for the presence of Lactobacillus and Pediococcus. These bacteria are anaerobic, heat-sensitive bacteria, and are called "beer spoilers" because they are most often associated with post wort production contamination.
Wallerstein Differential (WLD)
General detection media used to check for bacteria and Saccharomyces-type wild yeast. Bacterial contamination seen on these plates is termed "wort bacteria" because they are most often associated with wort contamination, usually doing most of their damage before the onset of fermentation.
About Saccharomyces cerevisiae variant diastaticus
At White Labs, we do everything possible to detect for undesired organisms within our process and cultures. Through genetic testing, we have determined that some strains in our core catalog of yeasts contain the glucoamylase gene (STA1) as a possible indicator of S. cerevisiae var. diastaticus. Since brewers yeast are natural hybrids, it is not uncommon for some strains to display elements of the STA1 gene that results in higher typical levels of attenuation but are not considered contaminants. Contaminants of S. diastaticus can cause over-attenuation in beer by fermenting dextrins (unfermentable sugars). The strains we carry with known var. S. diastaticus genetics have been validated to perform without excessive over-attenuation through many years of experience, internal and external fermentation data. These strains are noted in our strain listing on our website.
About our S. diastaticus Analysis Procedures
All of our yeast strains are typed using polymerase chain reaction (PCR). This assay takes advantage of the fact that S. diastaticus has an extracellular glucoamylase that S. cerevisiae does not. The primer set used has strong specificity to the STA1 gene in S. diastaticus and will not generate an amplicon with conventional brewer's yeast, typical beer spoilage yeast, or typical beer spoilage bacteria (1).
Yamauchi, H., Yamamoto, H., Shibano, Y., Amaya, N., and Saeki, T. Detecting Beer Spoilage Yeasts using the Polymerase Chain Reaction. J. Am. Soc. Brew. Chem. 56(2):58-63, 1998