Brewing yeasts are yeasts used in the brewing Process and which have certain properties, including:

• The ability to convert certain sugars to alcohol
• Reduce diacetyl thereby avoiding 'butterscotch' flavours in the beer

These fall into two main categories:

• Saccharomyces carlsbergensis
• Saccharmoyces cerevisiae

To ensure purity of strain, a 'clean' sample of the yeast is stored in a laboratory environment at refridgerated temperature. After a certain number of fermentation cycles, a full scale propagation is produced from this laboratory sample. Typically, it is grown up in about three or four stages using sterile Brewing wort and oxygen.