Conditioning, Clarification, Stabilization
Today with the use of modern equipment for refrigeration, carbonation, and filtration, obviates the need for secondary fermentation and a long cold storage. The green beer undergoing maturation is fully attenuated and virtually free from yeast, which is achieved because of higher fermentation temperatures and a diacetyl rest. Modern practices have shortened fermentation and lagering times, and uses rapid cooling after fermentation to aid yeast settling (Sections 14.2, 14.3).
Flavor and Aroma Changes
Flavor maturation is generally considered the most significant outcome of conditioning. Conditioning involves many biochemical, chemical, and physical reactions, many of which are not completely understood and elucidated. Vicinal diketones (VDKs, such as buttery-tasting diacetyl and honey-like 2,3-pentanedione), hydrogen sulfide (rotten eggs), and acetaldehyde (green apples) are primarily responsible for undesirable flavors at the end of primary fermentation. VDK compounds are generally considered objectionable in lighter-bodied lagers but sometimes desirable in ales and more full-bodied beers.
Conditioning tanks or commonly referred to as bright beer tanks are either horizontal or cylindroconical and are usually constructed of AISI 304 stainless steel, as shown in Figure 14.1. Horizontal tanks usually range in size of 100 to 500 hL while vertical cylindroconical tanks can be up to 6,500 hL in size (Briggs et al., 2004). The greater ratio of surface area to beer depth for horizontal tanks provides a distinct advantage over vertical tanks in the conditioning of beer.
If the sole purpose of the tank is for conditioning, there is no restriction on the height of the tank. However, if the tank is also used for fermentation the height can’t exceed 15 meters (Briggs et al., 2004). This has to do with the hydrostatic pressure on the yeast during fermentation.
Bright beer tanks lend themselves readily to temperature programming. The conditioning temperature can be automatically controlled on a preset program by means of a temperature recorder-controller operating the vessel jackets on the walls and the cone. Temperature probes are located at different depths to detect variations in temperature due to circulatory currents.
Coolants. For temperature control of cylindroconical tanks the brewer can either use direct or indirect cooling (Chapter 22, Brewery Refrigeration):
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