Largecapacity fermenters

In modern breweries, there has been a trend towards batch sizes larger than those achievable with traditional vessel designs. To meet this demand several fermenter

Mild Steel Cement Lined Pipe Design

Bottom drain

Bottom drain

Top trough attemperation

Top trough attemperation

Burton Union Fermentation System

Fig. 5.7 (a) Schematic, (b) detail and (c) side elevation of a 44 cask double Burton Union set.

Fig. 5.7 (a) Schematic, (b) detail and (c) side elevation of a 44 cask double Burton Union set.

types have been developed. These are all of the closed design and now are invariably fabricated from stainless steel. Earlier forms were constructed from mild steel, aluminium or lined concrete. Apart from the need to be able to control and monitor the fermentation, a common design criterion is the need to fit numbers of tanks into a minimum of floor space. With one exception, the spheroconical fermenter, this has been accomplished by adopting a cylindrical geometry. In all cases, the yeast crop is harvested from the bottom of the vessel.

5.4.1 Cylindrical fermenters

The simplest vessel design takes the form of a cylinder with two dished ends. The vessel may be oriented in a horizontal (Figs 5.9(a) and (b)) or vertical plane (Fig. 5.10). Typical capacities are 500-2000 hi. Both vessel types are of a closed design and so they have good hygienic properties and collection of carbon dioxide is possible. Attemperation is via wall cooling jackets and temperature control is usually automatic. In order to insulate the vessels from the external environment they must be lagged, and, if located outdoors, weatherproofed. There is a single main, which is used for both addition of wort at the beginning of fermentation and removal of yeast and green beer at the end.

Yeast cropping is a more efficient operation from the vertical vessel since the yeast collects as a more compact mass in the smaller area of the dished base. In the case of

Burton Union Schematic
Fig. 5.8 Images from the Burton Union room (courtesy of the Bass Museum. Burton-upon-Trent, England).

the horizontal vessel the yeast sediments along the entire long axis of the base. To facilitate its removal horizontal vessels are inclined slightly towards the exit main. Even so, very flocculent strains may be very difficult to crop and the use of such yeast with these vessels is not recommended.

In view of the different aspect ratios of horizontal and vertical vessels it would be predicted that mixing due to the natural agitation of fermentation would be much less in the former (see Section 5.1.4). In view of this, it might also be predicted that fermentation performance would be markedly different in each vessel when using similar worts and yeast strains. In particular, faster fermentation rates due to better mixing would be expected in the vertical vessel. Experience does not necessarily bear this out. The data in Table 5.5 shows residence times for similar high-gravity lager fermentations performed in either 800 hi horizontal cylindrical vessels or 1600 hi vertical cylindrical vessels. As may be seen, there were no significant differences in fermentation performance between the two types of vessel. However, in this case the yeast strain was a non-flocculent type, which possibly provides an explanation for the result. With a more flocculent variety, the horizontal vessel would be expected to give a slower fermentation. To overcome this shortcoming and improve circulation, horizontal cylindrical fermenters are often fitted with slow speed mechanical stirrers.

Both types of vessel can be arranged in groups, or tank farms, to maximise the utilisation of available floor space. From a civil engineering standpoint, this is more

C02 exhaust

C02 exhaust

Vessel Manways
Upper manway

door

Fig. 5.9 Horizontal cylindrical fermenter. (a) Side elevation, (b) End-on.

door

Fig. 5.9 Horizontal cylindrical fermenter. (a) Side elevation, (b) End-on.

difficult with horizontal vessels. If they are located within a building, the tanks will probably be arranged on a number of floors. If they are outdoors, the vessels may be stacked in vertical arrays but substantial and expensive supporting structures are needed, and, furthermore, a complex arrangement of service mains is required. On the other hand, vertical cylindrical tanks can be conveniently located in close standing groups with a much simpler supporting structure. If they are outdoors there is no

Gravity Brewing System Plans
Fig. 5.10 Vertical cylindrical fermenter.
Table 5.5 Fermentation cycle times for a high gravity lager performed in 1600 hi vertical or 800 hi horizontal cylindrical vessels (C.A. Boulton & A. Oliver, unpublished data).
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