Wort Cooling, Clarification, Aeration
Wort Cooling
Nearly all commercial breweries use some form of fluid-cooled heat exchanger for cooling the wort for fermentation. The wort collection temperature is usually a function of the yeast used and the style of beer being produced. Traditionally this is about 15 to 22°C (59–71.6°F) for ales and 6 to 12°C (42.8–53.6°F) for lagers, but other temperatures are used (Briggs et al., 2004). In traditional breweries, the hot wort was cooled in a shallow open vessel often referred to as a “coolship.”
Type of Heat Exchangers
Heat exchangers can provide the necessary heat treatment for the brewing process of beer, such as cooling, pasteurization, fermentation, aging, and cleaning brewing equipment.
Plate and Frame Heat Exchangers
A plate and frame heat exchanger consists of a series of plates that connects to a large frame. Gaskets placed around the edges of the plates maintain the spacing between each plate (Figure 11.1). The plates have four openings at each corner, and the gaskets are placed such that the flow of hot and cold fluid alternates between plates. Because the surface area of the plates is quite large, and because the plates can be made from very thin material, plate and frame heat exchangers can be very efficient at transferring energy.
Shell and Tube Heat Exchangers
The number of rows of kernels makes for easy identification of two- and six-row varieties. In six-row varieties, two-thirds of the kernels are twisted in appearance because of insufficient space for symmetrical development.
Shell and Coil Heat Exchangers
Although various configurations are available, the basic and most common design consists of a series of stacked helically coiled tubes. The tube ends are connected to manifolds, which act as fluid entry and exit locations. The tube bundle is constructed of a number of tubes stacked atop each other, and the entire bundle is placed inside a casing, or shell. To effectively optimize thermal and hydraulic requirements, the number of tubes (coils) along with their spacing and length may be varied.
Single- or Two-Stage Cooling
The cooling operation can be achieved with a single-stage system using cold-water jacketed-tank to cool the hot wort to fermentation temperature. Typically, the water in the tank is cooled to between (3–10°C, 37–50°F) with typically averaging around 5 degrees C (41°F).
Single-Stage Cooling
The cooling operation can be achieved with a single-stage system using cold-water jacketed-tank to cool the hot wort to fermentation temperature. Typically, the water in the tank is cooled to between (3–10°C, 37–50°F) with typically averaging around 5 degrees C (41°F).
Two-Stage Cooling
In a two-stage system the first stage utilizes water to remove the bulk of the heat, cooling the incoming wort. In the second stage, the wort is cooled to the fermentation temperature by glycol/water mixture that has been cooled by a chiller or by direct expansion using a refrigerant.
Formation of Cold Break
As the clear hot wort is cooled, the previously invisible coagulum loses its solubility and precipitates. The precipitate is referred to as the cold break and begins forming at about 60 degrees C (140°F) (De Clerck 1957). The cold break mostly consists of protein-polyphenol (tannin) complexes, whereas the hot break is mostly proteinaceous. The cold break also has a higher level of carbohydrates (primarily beta-glucans) than hot break (Gordon, 1991). Highly modified malts yield a higher percentage of polyphenols in cold trub than do less-modified malts, while under-modified malts yield more protein and beta-glucans and relatively fewer polyphenols (Barchet, 1994).
Factors Affecting Quantity of Cold Break
The total dry weight of cold break is between 15 and 30 g/hL, accounting for about 15 to 30 percent of the total trub material precipitated during cooling and boiling of the wort. The actual amount produced in a given wort depends on numerous factors, such as malt modification, mashing program, wort temperature, the presence of hops, and the rate of hot break removal.
Click on the following topics for more information on wort cooling, clarification, and aeration.
