Info

Epoxy

Excellent

Good

Good

Good

Polyester

Excellent

Good

Excellent

Excellent

Polyurethane

Excellent

Excellent

Good

Excellent

Methylmethacrylate

Excellent

Good

Good

Excellent

Vinylester

Excellent

Good

Excellent

Excellent

The floors of fermenting rooms must be free draining and drainage channels should not contain stagnant water, which can be a source of odours that could potentially taint beers. Equipment within the room should be located, wherever possible, away from the walls to provide adequate access for cleaning and disinfection. Windows should be protected with grilles to prevent the entry of insects. Measures should be taken to prevent entry of rodents. Ceiling design is of particular importance where open vessels are used because of the potential for foreign materials falling into the beer. To minimise the risk, the material used for the ceiling must be smooth and non-peeling. If possible there should be no fittings, mains or trunking located directly above vessels. If this is unavoidable, a sealed false ceiling is advisable. Light fittings should be shrouded. Doors leading to the room must be kept closed to minimise the risk of atmospheric contamination and access should be restricted to essential personnel. If the consequences of contamination are considered to be very severe (e.g. immobilised yeast reactor or a continuous fermentation system), a slight positive pressure should be maintained to further reduce the likelihood of airborne contamination (see Section 8.1.4.2). Ideally but rarely, the room should be maintained at a constant temperature and humidity to prevent the formation of condensation. This is of particular importance where the room is refrigerated.

The most common hygiene problem encountered in fermenting rooms (and other areas within the brewery) is the development of mould growth. These microorganisms are particularly adept at colonising surfaces, particularly where there is persistent moisture. Their habit of proliferating via airborne spores promotes rapid spread of any infection. They will grow readily on most surfaces, including stainless steel. In fact, the black mould, Geotrichum candidum, is often referred to as 'machinery mould' because of its propensity for producing slimy growth on metal surfaces (Phipps, 1990).

The consequences of mould growth in fermenting rooms can be severe and unexpected. Unchecked mould infection is associated with corrosion of metals and other materials. The by-products of their metabolism are associated with 'musty' off-flavours in beer. In one instance, a problem of over-attenuation in an unpasteurised beer was thought to be the result of contamination with amylases, introduced as the result of growth of the mould Rhizopus oryzae on an unclean flexible hose (D.E. Quain, unpublished data).

Prevention of microbial contamination of the room should be achieved via combination of good initial design followed by careful management. A number of paints, epoxy resins and mastics are available that contain biocides and these should be used where appropriate. In addition to moulds, these are effective against algae, bacteria and lichens. The surfaces of the room and the plant should be washed regularly with a disinfectant. Phipps (1990) recommends ammonium diproprionate as being particularly effective against moulds since it has good residual activity. Incipient mould infections may be recognised as an increase in the numbers of airborne spores. It is good practice to check for this using a suitable microbiological air-sampling device (see Section 8.1.4.2).

5.2.2 Temperature control of fermenting rooms

Where fermenters are enclosed totally within a room, the latter must assist with vessel attemperation. Traditionally, fermenters and conditioning vessels were located within cellars or caves to take advantage of the low and relatively constant ambient temperature. Vessels were constructed from materials such as wood, which have low thermal conductivities, and assist in minimising heat pick-up from the room. In the United Kingdom, ales tend to be fermented at relatively high temperatures (18 to 22°C) and presumably this reflects the limits of temperature control that were available before the advent of effective refrigeration. Traditional lager beers were fermented at temperatures lower than ales (6 to 12°C). The long secondary fermentation associated with these beers was performed at even lower temperatures (1 to 10°C). Historically, production of lagers evolved in the countries of central Europe and Scandinavia where the relatively colder winter climate facilitated attemperation. For example, the Pilsner Urquell brewery in the Czech Republic still uses wooden fermenting vessels of 25 hi capacity. The vessels have no internal attemperation but they are located in a cellar. The pitching temperature is 4.8°C and during the 12 day fermentation the temperature rises to no more than 8.5°C (Hlavacek, 1977).

Fermentation and conditioning could be practised throughout the entire year in the United Kingdom only when a means of artificial cooling was devised. Initially, this was achieved by placing blocks of ice in fermentation rooms (de Clerck, 1954). Of course, this was expensive and inefficient and when the requisite technology became available, rooms were chilled using cold air delivered via a refrigeration unit. Less ideally, fermenting vessels, or more often conditioning vessels, may still be attemp-erated using room refrigeration. This requires that the room be insulated but not the vessels. The latter should be constructed from materials with high coefficients of thermal conductivity. In addition, there must be adequate ventilation to avoid a build-up of dangerous concentrations of carbon dioxide and care should be taken to avoid condensation.

In modern installations, the use of refrigerated rooms has been almost entirely superseded by the use of insulated vessels with individual facilities for attemperation. This has been accompanied by the use of rooms of light construction with little or no specific facilities for temperature control.

5.2.3 Control of carbon dioxide concentration

Gaseous carbon dioxide produced during fermentation is a serious health hazard. The risk to brewery personnel is particularly grave where open fermenters are used and there is no facility to collect the gas as it is evolved. It is essential to provide sufficient ventilation within the fermentation room so that the gas may be dissipated safely. The carbon dioxide concentration within the fermenting room should be monitored at all times using an automatic monitor fitted with an audible alarm.

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