Fermentation
Post-Fermentation
When fermentation is complete the beer must be rendered into a form suitable for consumption. Many options are possible depending on the type of fermentation. Beers are either subject to secondary fermentation or more typically to conditioning.
Secondary Fermentation
Beers that are subject to a secondary fermentation are removed from the primary fermentation vessel after the bulk of the yeast has been removed and transferred for further processing, either in cask or bottle (Chapter 13). In the case of secondary fermentation, conditioning involves a period of storage in which flavor maturation occurs and this requires the presence of viable yeast cells. Such types of beers are comparatively rare. In the case of traditional top-fermented beers, moderate cooling is applied at the end of primary fermentation, usually to between 10 and 15 degrees C (50–59°F). When emptying the tank, the aim is to achieve a suspended yeast count in the region of 1 million (1x106) cells per mL and a residual fermentable extract equivalent to roughly 0.75°P (Boulton et al. 2006).
Conditioning
Conditioning includes all transformations between the end of primary fermentation and the removal of yeast from the beer in preparation for packaging (Chapter 14). Some of the downstream processes following conditioning include clarification, stabilization, filtration, carbonation, pasteurization/sterile filtration, and packaging.
Bright Beer Tanks
Bright beer tanks are called “bright” because of the clarity of the beer they produce (Figure 12.14). When beer goes from a fermenter to a bright beer tank, the yeast is filtered out first. This extra layer of filtration before undergoing further maturation and carbonation produces a clearer beer, which some brewhouses prefer. Bright beer tanks have a cylindrical center, but they have a flat bottom.
Reducing Oxygen Pickup. Bright tanks must be purged of air before they are filled. The purge should also be conducted at a low pressure (5 psi is recommended) for a long period of time (3–4 hrs for a 30-barrel tank, or roughly 1 hL per 10 barrels) (Skinner, 2020). If the pressure is too high it will cause turbulence within the tank it will prevent the air from being fully expelled by carbon dioxide.
Unitanks
Alternatively, with a single tank (e.g., unitank) operation both primary fermentation and conditioning are performed in a single vessel. In this mode of operation, the green beer is chilled to between 2 and 4 degrees C (36 and 39°F) at the end of primary fermentation (and possibly a period of warm conditioning) to sediment the yeast.
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