Wort Cooling, Clarification, Aeration
Cold Wort Clarification
The brewer has the option to either to remove the cold break or not remove the cold break. Opinions vary as to whether cold break should be removed at all before transferring the wort to the fermenter. However, excessive amounts of break can cause flavor and process problems in beer brewing such as the presence of sulfury (cabbage-like) flavors in the beer or poor fermentation performance—often associated with the trub physically binding to the yeast.
Methods of Cold Break Removal
Some brewers reduce the amount of cold break by sedimentation, air flotation, wort filtration, whirlpools, and by centrifugation.
Sedimentation
The simplest way to remove cold trub is through cold sedimentation, which requires only one vessel—a starter tank—which can be used with pitched or unpitched wort. Because wild yeast and bacteria are a problem, care must be taken to ensure that the starter tank is sanitary, particularly if the wort is unpitched. Shallow vessels rather than cylindroconical tanks make the best settling tanks. Deeper vessels require more time but can benefit from an addition between 10 and 20 g/hL coarse diatomaceous earth (Barchet, 1994).
Removing Cold Break from Pitched Wort. For long lag times, Barchet recommends pitching the yeast and allowing the chilled, aerated wort to settle between 6 and 24 hours before racking to the fermenter and leaving the sediment behind (Barchet, 1994).
Flotation
Another method of cold trub removal involves the flotation using vertical vessels with an even or slightly angled bottom. Cold break particles adhere to the surface of air bubbles that are forced continuously through cooled wort from the bottom of the tank by a Venturi tube and a mixing pump. A flow rate of 20 to 60 liters of air (not oxygen) per hectoliter is required (Carey et al., 2006). The cold break particles attach themselves to the air bubbles, and a layer of foam is formed on the surface of the wort.
Pressure Leaf Filtration
Pressure leaf filtration using diatomaceous earth (DE)is the most effective means of removing cold trub and is likely to be used by larger breweries. Diatomaceous earth filtration is not effective in removing hot break since the filter aid dissolves in hot wort. Typically, coarse diatomaceous earth is used, and the best results occur at low temperatures, i.e., 0 degrees C (32°F).
Whirlpool
An alternative solution is the whirlpool, where the wort is pumped tangentially into a cylindrical vessel. This creates an even, rotating stream. The solid particles suspended in the rotating liquid will separate due to friction (tea cup effect), migrate to the bottom center, and coalesce to form a cake.
Centrifuge
The hot wort can be clarified by means of efficient, self-cleaning centrifuges; these, however, will only work reliably if the wort—trub mixture is added homogeneously. This can usually be achieved by means of an intermediate hot wort tank with a stirring mechanism. Centrifugation has the major advantage in that the times for sedimentation and transfer can be drastically shortened.
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