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and the value for Z' is taken as 6.94°C, the value reported for the 'abnormal yeast'. The Z-value concept and its role in calculating lethal rates (PUs) have come in for repeated criticism over the years since 1951. The focus of much of this attention has been the Z-value used in this calculation, its origin and relevance. In a persuasive piece of work, McCaig et al. (1978) reported the failure of a flash pasteuriser operating at 26.5 PU to achieve commercial sterility. Further investigation showed the presence of L. brevis with a higher Z-value than 6.94°C. Depending on the heating menstruum, the Z-value for this organism was 15 (beer) or 20.2 (buffer, pH 7). With these observations in mind, McCaig et al. (1978) concluded that for the lethal rate approach to have validity would require each brewery to determine the Z-value for their organisms and beer! Similarly, Tsang and Ingledew (1982) reported Z-values (°C) of 11.2 (P. acidilactici), 12.3 (L. delbrueckii), and 15.4 (L. frigidus) for organisms tested in degassed 5% abv lager. Molzahn et al. (1983) also reported a Z-value of 12.4°C for L. brevis in alcohol-free lager. Collectively such results are significant for two reasons. First, they challenged the universal Z-value but also demonstrated the critical role of the heating menstruum in microbial thermal resistance. The later concern can be extended to include the experimental approach to assess heat resistance (four distinct approaches were reported by O'Connor-Cox et al., 1991a) as well as the physiology of the laboratory-grown micro-organisms being tested. It is tempting to conclude that, as noted above in the discussion on biofilms (Section 8.1.4.1), laboratory cultures of micro-organisms may bear little physiological relevance to those encountered in the real world. Further concern was heaped on this approach by Tsang and Ingledew (1982) who identified three scenarios that undermined the validity of using the Z-value, and concluded bluntly, 'Z is not a measure of heat resistance'.

Having so roundly dismissed the Z-value, Tsang and Ingledew (1982) proposed an alternative approach used in the food canning industry - the 'D-value' or decimal reduction time - to describe the thermal behaviour of micro-organisms. As ever, this measure has been defined in a variety of ways. Accordingly, Molzahn et al. (1983) described D 'as the time required at any temperature to reduce the number of survivors by one power of 10'. Whereas Beer Pasteurisation Manual of Good Practice (European Brewery Convention, 1995) defined the D-value as the 'time needed at a given temperature to inactivate 90% of the viable population for example from 100% to 10%'. In the hypothetical example presented in Fig. 8.25, a test organism has been heated at 60°C and the number of survivors (as a logarithm) plotted against heating time. From this relationship, the D-value or D60 value is 1.7 minutes. Although subject to the same experimental constraints and concerns as the Z-value, this approach enables the efficacy of a time/temperature combination to be predicted. If, for the example presented in Fig. 8.25, the loading of the test organism was 20 x 103 cells 1 1 (i.e. 20 cells ml *) for every 1.7 minutes at 60°C, the viable loading will reduce by 99% (20 x 102 cells 1 99.9% (20 cells 1 99.99% (2 cells 1 and so on.

D-values determined at various fixed temperatures can be plotted against temperature to give a 'phantom thermal death curve' (Tsang & Ingledew, 1982). Examples of such curves are presented in Fig. 8.26. It is apparent from this data that at a fixed temperature there is a wide variation in D-value (e.g. D45). Further, the gradients the phantom death curves vary widely between micro-organisms. Consequently, the yeast P. membranifaciens (D45 = 62.5 minutes) is more resistant at 45° C than the bacterium L. frigidus (D45 = 2.9 minutes). However, the tables are turned at

Fig. 8.25 Example of a survival curve-semilogarithmic plot of viable cell count against time of incubation at a fixed temperature (°C).

Time (mins)

Fig. 8.25 Example of a survival curve-semilogarithmic plot of viable cell count against time of incubation at a fixed temperature (°C).

Fig. 8.26 Phantom thermal death curves for (■) P. membranifaciens, (♦) P. anomala, (A) lager strain of S. cerevisiae, (x ) L. frigidus and (*) L. delbrueckii (from data reported by Tsang and Ingledew, 1982).

51°C where L. frigidus (D51 = 1.7 minutes) is more resistant than P. membranifaciens (D5i = 0.4 minutes). Correspondingly the D60 values are 0.44 (L. frigidus) and 0.00025 minutes (P. membranifaciens). The Z-value for each organism can be calculated from the relationship between D-value and temperature from the equation Z = (T2-TO/flog Di-log D2).

To further confuse the issue it is apparent from the literature that, as with the Z-value, the D60 value varies widely between micro-organisms (European Brewery Convention, 1995). In addition to previously mentioned considerations such as laboratory cultivation and associated physiology, the heating menstruum influences the heat resistance of challenged micro-organisms. Factors include pH and concentration of ethanol, carbon dioxide, and fermentable sugars. Garrick and McNeil (1984) demonstrated that a decrease in pH decreased the D value for a Lactobacillus isolate. Not surprisingly, the impact of ethanol on thermal death has received wider study - the headline being that ethanol is notable for its augmentation of heat killing. Figure 8.27 clearly shows the impact of ethanol together with temperature on the reducing the D-values for a spoilage Lactobacillus isolate (Adams et al., 1989). This explains why conventional pasteurisation regimes are unacceptable for low/non-alcohol beers which require elevated PU inputs to assure microbiological stability (Molzahn et al., 1983; Kilgour & Smith, 1985; Adams et al., 1989).

Fig. 8.27 Impact of temperature (♦ 55°C, ■ 60°C, A 65°C) and ethanol on D-values for Lactobacillus E93 (from data reported by Adams et al., 1989).

These studies on beer composition go some way to justify the commitment of the various groups to unravelling the complexities of the D-value and Z-value. However, this insight has prompted Garrick and McNeil (1984) to suggest that pasteurisation regimes may require to be established for each beer according to its composition. The downside is that such experiments are at best 'difficult', a concern that is exacerbated by the lack of a 'standard' method. So much so that O'Connor-Cox et al. (1991a) were moved to conclude that the data on 'the relative heat resistance of bacterial and yeast species is confusing and somewhat incomplete'. This, together with the concern that designing pasteurisation regimes around one atypically thermorésistant organism (e.g. the 'abnormal yeast' of Del Vecchio et al., 1951) is generally inappropriate, has to an extent undermined such studies. Under the circumstances, it is no surprise that many of these hard-won publications recommend that further work is undertaken to explore the relationship between time, temperature and microbiology (Tsang & Ingledew, 1982: Garrick & McNeil, 1984; Kilgour & Smith, 1985). The absence of such subsequent studies is perhaps a reflection of a change of attitude to pasteurisation. As noted earlier, it is no longer acceptable for pasteurisation to act as a 'backstop' to mend poor product hygiene. Initiatives such as HACCP and ISO quality standards have focused on prevention of (microbiological) problems. Accordingly, the focus has been on reducing the microbial load to pasteuriser. In terms of process control, this has been recognised as the most effective step in assuring the success of pasteurisation together with reducing the number PUs to achieve 'commercial sterility'. This overcomes many of the complexities and reservations (see for example Kilgour & Smith, 1985) of establishing pasteurisation regimes from D-and Z-values.

Typical pasteurisation regimes. Despite the foregoing debate, PUs remain the accepted currency of thermal processing of beer. The number of PUs required to achieve 'commercial sterility' remains a moot point! Laboratory studies over the years have reported that only 1-5 PUs are necessary (Del Vecchio et al., 1951; Tsang & Ingledew, 1982; Garrick & McNeil, 1984). In practice, as a rule of thumb, 15 PUs (equivalent to 15 minutes at 60°C) have been applied 'universally' across the brewing industry worldwide (Del Vecchio et al., 1951; Tsang & Ingledew, 1982; O'Connor-Cox et al., 1991a, b). However, as noted by Dallyn and Falloon (1976) such regimes in tunnel pasteurisers correspond to 30 PU when heating-up and cooling times are included. For many, this is perhaps an idealised, optimistic view of routine pasteurisation regimes used to assure commercial sterility. Some older tunnel pasteurisers do not have the process capability to achieve relatively low PUs. For others, there is a natural tendency to operate at higher temperatures and times to meet the 'just in case' need to satisfy the unexpected microbial loading (the so-called 'safety margin'). Further, a common and unfortunate practice is to inexorably increase pasteurisation regimes (particularly flash pasteurisation) in response to a downturn in microbiological results, real or anticipated trade problems. Unfortunately, the 'after the event' reduction in elevated pasteurisation temperature/time is not pursued with the same vigour or commitment. This invariably results in pasteurisation specifications being higher than strictly required by the microbiological loading pre-pasteuriser.

Although clearly a local issue and one that should be 'tailor-designed to suit the brewery in question' (O'Connor-Cox et al., 1991b), typical PU values have been reported. For example the EBC (European Brewery Convention, 1995) has reported PUs to vary between beer styles, ranging from 15-25 (lager), 20-35 (ales and stouts), 40-60 (low-alcohol beers) and 80-120 (non-alcoholic beers). As noted above, such variability in pasteurisation requirements reflects the impact of product composition on thermal killing of micro-organisms. However, according to O'Connor-Cox et al. (1991b), most North American breweries (with presumably conventional products) operate between 5 and 15 PU which, they suggest, may provide an 'excessive safety margin'. Similarly in the UK, as long ago as 1976, there was anecdotal evidence that breweries operate routinely between 10 and 12 PU (Dallyn & Falloon, 1976; O'Connor-Cox et al. (1991b). Whatever the reality of'how many PUs', there is little doubt that PUs are declining worldwide. This is a consequence of drivers such as reducing energy utilisation and the need to minimise thermal damage to product, ambitions which are made possible by improvements in process capability (hardware and product hygiene).

QA of pasteurisation. The ultimate measure of the success of pasteurisation is the achievement of 'commercial sterility'. In other words, there is no suggestion of microbial growth over the shelf-life of the product. In reality, pasteurisation regimes invariably achieve this objective, presumably through the inclusion of comfortable 'safety margins'! Process assurance is typically achieved through setting tight quality standards and subsequent monitoring. Pre-pasteuriser microbiological monitoring is usually via a continuous 'drip' sampler of the feed beer. Although inevitably retrospective, this approach enables trend analysis and the identification of deteriorating (or improving) performance. Microbiological monitoring postpasteuriser ex-final package is increasingly viewed as unnecessary or is a minimal 'comfort' analysis. Again, the results of any analysis are historical and invariably of little statistical relevance. This later point is exemplified by the microbiological analysis of two cans/bottles every hour from a line operating at 2000 cans every minute!

A preferable route is to monitor the process such that its effectiveness is assured. In the case of tunnel pasteurisers, thermographs have long found application in monitoring time and temperature. Monitors such as the 'Redpost' enable various quality parameters (transit time, time above 60°C, maximum temperature, and total PUs) to be downloaded and printed (European Brewery Convention, 1995). Flash pasteurisers are increasingly sophisticated, and accordingly key parameters such as flow rate, pasteurisation temperature, outlet beer temperature and downstream beer pressure are computer controlled to achieve the desired PUs (European Brewery Convention, 1995). In passing Beer Pasteurisation Manual of Good Practice (European Brewery Convention, 1995) provides worked 'how to' calculations to determine the PUs from tunnel and flash/plate pasteurisers.

An alternative approach, that has found application post-pasteurisation, is to assay for heat labile yeast derived enzymes that can be found in beer (European Brewery Convention, 1995). The yeast cell wall enzyme invertase (Sections 4.1.2.2, 4.4.2.4), which cleaves sucrose to glucose and fructose, was first introduced in 1902 (Ene-voldsen, 1985) as an 'all or nothing' test for pasteurisation. Although considered to be inactivated by 5 PU, there is a view (Rader, 1979; McNeil et al., 1984) that at pHs of 4 and above the invertase method should be used to quantify beers exposed to 10-15 PUs. Building on this approach, Enevoldsen (1981, 1985) proposed a similar approach based on the detection of melibiase, an enzyme found exclusively in the cell wall of lager strains of S. cerevisiae (Section 4.1.2.2). Depending on the pH of the beer, Enevoldsen (1985) reported being able to estimate the heat treatment of lager beers between 30 and 125 PUs. Work by Reeves et al. (1991) showed melibiase to have a Z-value of 3.5°C and a D60 of 185 minutes in a beer of 4.2% (v/v) ethanol and a pH of 4.2. These workers, whilst noting the method's potential application for assurance of thermal killing of yeast, add the caveat that its usefulness is specific to pasteurisation regimes at 60°C and its use should be modelled for each potential beer.

Flavour impact of pasteurisation. The drive to reduce pasteurisation so as to improve product quality is firmly rooted in the negative flavour characteristics attributed to thermal processing. For an excellent, general review of the complex field of flavour stability, the reader is directed to the review of Bamforth (1999). O'Connor-Cox et al. (1991a) described over-pasteurised beers as being 'oxidized, bread-crust-like, or possessing a cooked quality'. Chemically, Bamforth (1986) was able to demonstrate the formation of carbonyl compounds on pasteurisation and Back et al. (1992) ascribed 2-furfural, heptanal and other compounds as indicators of'thermal tainting'. It is generally accepted that 'cooked' characters can be avoided, or at least managed, by reducing pasteurisation regimes and, particularly with tunnel pasteurisers, putting an upper 'reject quality limit' on over-pasteurised bottles and cans. A further critical factor in flavour stability is to minimise the dissolved oxygen content of beer during processing and packaging (Bamforth, 1999).

8.2.1.3 Sterile filtration. The development of sterile filtration as an alternative process to pasteurisation has been driven by benefits to product quality together with the consequent marketing opportunity to differentiate such products to the consumer. Although appropriate to any packaging format, sterile filtration has found especial application for can and bottle (including PET, Reid et al., 1990) products. Replacing pasteurisation with a cold filtration process has supported marketing claims that such products are 'natural', 'fresh' or 'clean'. Indeed, it is a legitimate claim that such beers will not suffer from 'cooked', 'bread-like' or 'pasteurised' flavours described above. Although seemingly new technology, sterile filtration of beer dates back to 1931 with a production unit being used in England (Ryder et al., 1994). Since then sterile filtration has taken off, albeit selectively, representing 63% of the Japanese market in 1990 (Ichikawa & Takinami, 1992) and some 25% of the American market (Ryder et al., 1994). European breweries have been more conservative in applying the technology with the demands of franchise brewing and the need to match international brands, often driving investment in sterile filtration. Arguably, the wider implementation of sterile filtration has been minimised by the lack of consumer 'pull' and hampered by the more stringent demands of process and product hygiene.

Like pasteurisation, sterile filtration achieves 'commercial sterility' with a typical specification of < 1 yeast cell 1 1 and < 1 bacterial cell 1 1 (European Brewery Convention, 1999). Sterile filtration cannot simply be 'bolted in' nor can it be a 'solution to poor hygienic practices upstream' (Dunn et al., 1996). Users of the technology recognise that it is 'higher risk' than pasteurisation (see Fig. 8.21) and repeatedly emphasise the need for a step change in hygienic practice and standards throughout the brewery. Working hand-in-hand with this philosophy is the attitude of the people in the brewery who must have a 'sanitary mindset' (Ryder et al. (1994). The take home message is simple! Sterile filtration cannot operate in isolation. Steps must be taken to control and limit the incoming microbial load both to achieve 'clean' beer but also to satisfy process flow rates. The hygiene of subsequent downstream packaging oper ations is of critical importance and must be controlled to assure microbiological stability. Users of the technology have recognised the need for total hygiene management and, accordingly, have imposed aseptic clean rooms or covering shrouds (Ichikawa & Takinami, 1992; Ryder et al., 1994) around the filler and associated environments. The very real risk of airborne contamination (Section 8.1.4.2) is typically met by the use of clean air conditioning, positive pressure and occasionally air locks. Inevitably, CiP and sanitation is of paramount importance to the routine success of sterile filtration. The regimes used by Sapporo in Japan (Ichikawa & Takinami, 1992) and Miller in the USA (Ryder et al., 1994) both major on the 'before and after' use of hot water (80-8 5° C) together with regular caustic CiP. Equally the threat of conveyor-mediated contamination (Section 8.1.4.2), is recognised and, consequently, is controlled (Ichikawa & Takinami, 1992; Ryder et al., 1994). These and other considerations are described by Schmidt (1999) in a useful practical overview of the lengths his brewery in Brazil has gone to in assuring the packaging of 'draft beer' in bottle.

As a process, 'filtration' is characterised by variety, be it filtration 'media' or configuration. Accordingly, it is inevitable that sterile filtration regimes vary widely between practitioners and, indeed, within individual companies (see the description of the various systems at Kirin in Japan - Takahashi et al., 1990). Although by no means definitive, sterile filtration operations typically consist of two to three steps (Dunn et al., 1996). First, a conventional kieselguhr filtration of beer from maturation or conditioning tank to a bright beer or holding tank. This step achieves clarification and colloidal stabilisation. In terms of microbial load (Dunn et al., 1996), this filtration step reduces yeast counts from 5 x 106 cells ml 1 to as little as < 500 cells ml 1 and bacterial counts from as high as 104 cells ml 1 to 10 cells ml 1. The second step essentially achieves sterile filtration. Here, the microbial load is reduced to a specification of typically < 1 yeast cell 1 1 and < 1 bacterial cell 1 1. As a further guarantee, some breweries include a further membrane filtration stage to assure 'sterility'.

For further details of sterile filtration, particularly to the options for filtration media and plant configuration, the interested reader is directed to Beer Filtration, Stabilisation and Sterilisation, Manual of Good Practice (European Brewery Convention, 1999).

8.2.2 In the trade

The ultimate objective of good process practice, HACCP, QA/QC systems, and real commitment in breweries is to produce beer of excellent microbiological quality. On leaving the brewery, the product in keg is 'commercially sterile' but will contain very low levels of yeasts and bacteria (perhaps < 1 cfu in a litre). On dispense, the product will inevitably pick up low levels of 'contaminants' which do no harm whatsoever to the product or the consumer. For the vast majority of restaurants, bars or pubs this is the normal state of affairs for retailing a foodstuff. This is achieved through good hygienic practices and regular cleaning of the dispense lines. This is important as it is universally accepted that 'dispense' is of critical importance to product quality and presentation. As is often said, 'people drink with their eyes'!

Unfortunately, there can be occasions and/or outlets where products are dispensed which are not 'bar bright' or which have obvious flavour defects. The reasons are numerous but include poor working practices, inadequate hygiene education, concern about 'losses', or simply a flagrant disregard for the importance of hygiene in general or line cleaning in particular. Unfortunately, far too many consumers have experienced poor-quality products 'in the trade' caused by microbiological contamination at dispense. Typical problems include flavour defects (acetic acid, diacetyl, phenolics etc.) and a haze or 'cast'. Although some consumers reject or complain about such products, the vast majority will 'vote with their feet' and leave the outlet or change products. The impact of poor product quality on brand and outlet loyalty is inestimable but can be assumed to be considerable.

There are no excuses for this situation! Reports on the impact of poor microbiological hygiene on product quality in the trade are not new. One of the first (Hemmons, 1954) described the wild yeast microflora found in cask beers at dispense (see Section 8.1.3.2). Much of the fundamental work on the microbiology of beer dispense originated from work by the late Jim Hough's team at the British School of Malting and Brewing at the University of Birmingham in England. Initially Hough et al. (1976) tracked both the microbial loading and microflora from keg filling to dispense. With hindsight it is not surprising that the results from this work 'pointed the finger' at the hygiene of dispense lines and taps.

Pointedly Hough et al. (1976) remarked on the 'dirty and unnecessary custom of bar staff immersing dispense taps in the beer whilst drawing into glasses' and added 'it is particularly objectionable when a dirty glass is refilled'. The reaction within the industry to these hard-hitting observations is not recorded but with general exception of glass hygiene (see Stillman, 1996) may be anticipated as being muted!

Subsequent work from the group at Birmingham focused in greater detail on the microbiology of dispense together with the materials used to make and clean beer lines (Harper et al., 1980; Harper, 1981; Casson, 1982). The microbial diversity of dispensed keg and cask beers was reported in Section 8.1.3.2 (Harper et al., 1980). Again the microbiology and 'handling' of the dispense tap received particularly withering comment. To wit, 'large numbers of yeast and bacteria were encountered, probably due to the aerobic conditions, infrequent cleaning and the practice of immersing the nozzle into the beer during dispense'. These 'field observations' are compelling both in their honesty and in insight. The report of Harper et al. (1980) is notable for the realisation that 'infection' is not static but mobile, moving from the tap into the line and, at the other end, from the line into the container. As noted elsewhere (Section 8.1.4.1), this paper was notable in the observations about the adhesion of micro-organisms to surfaces and, consequently, the difficulty in the removal or penetration of the 'biofilm' with line cleaning fluids. The subsequent paper (Harper, 1981) was similarly insightful in clearly demonstrating the difference in performance between yeasts maintained in the laboratory and those isolated from the real-world environment of the public house. The 'natural' isolates had clearly adapted to their environment growing more rapidly in beer and being significantly better at forming biofilms.

Harper's successor Duncan Casson focused his attention on the role of the line and, in particular, what polymer it was made of. Although at the time highly pertinent to the industry, the work described by Casson (1982) has been superseded by develop ments in beer line technology which, in part, were triggered by these earlier observations. Work at the University of Sunderland sponsored by one of the manufacturers (Premier Python Products) has extended the earlier work from Birmingham. Thomas and Whitham (1996) demonstrated major differences in the attachment of yeasts and bacteria to dispense tubing. Of the three then materials of construction, it is perhaps fortunate that by far the worst in terms of attachment - PVC - is no longer in use! Of the others, nylon was superior (in minimising attachment) over the more commonly used, MDP (medium density polythene). Although minimising microbial attachment to dispense line surfaces is an attractive concept, factors such as cost and gas porosity are bigger determinants of choice. At the end of the day the most effective route to minimising the detrimental effects of colonisation by yeasts and bacteria is the adherence to rules of basic hygiene coupled with regular and effective line cleaning.

In many respects the cleaning of dispense lines mirrors that of CiP in the brewery (Section 8.2.1.1). Although there is a wide range of proprietary line cleaning solutions, they typically revolve around a caustic detergent (sodium hydroxide, Table 8.10), a biocide (sodium hypochlorite, Table 8.12) and chemicals to soften water and ensure 'wetting'. Grant (1986) and Treacher (1995) have published useful and practical reviews on beer line cleaning. As a process there is little debate about line cleaning and the vast majority of practitioners understand what is 'best practice'. In summary after flushing the lines with water, the diluted detergent (as recommended by the supplier) is pulled through the lines and left to stand for about 30 minutes. Occasionally the detergent is 'moved' halfway through this process. Whatever, after the stand, the detergent is chased out by water, to drain. The detergent being 'soapy' provides a useful and simple measure of cleaning status, particularly in the assessment of line rinsing prior to bring beer back on line. Of course, these days line cleaning is far more complex than this 'potted version'! The excellent review of Treacher (1995) should be consulted for guidance on best practice. If performed correctly, it is assumed that the line is clean and accordingly validation is unnecessary. This view is subject to change as ATP bioluminescence provides realtime validation and is increasingly finding application as an audit tool (see Section 8.3.3.1).

There are a few variables in beer line cleaning. Like CiP, the detergent temperature can trigger debate. Some prefer to use cold water whereas others make up the detergent to be 'hand hot'. As to automation (which is increasingly available) most line cleaning is a manual operation and is performed by bar or restaurant staff. Inevitably the biggest and, undoubtedly most important debate is about the frequency of line cleaning. Treacher (1995) recommended that lines are cleaned 'to a minimum of every seven days' with the proviso that some products (low ABV, high sugar) may require cleaning more frequently. Further, Treacher (1995) noted that extending the cycle by two to three days 'can reduce the effectiveness of cleaning by up to 25%'! Although many would agree with these views, the reality is that the frequency of line cleaning in many establishments has been relaxed to every two weeks or more. There are many reasons for this. The most obvious is that line cleaning inevitably results in the loss of beer and, accordingly, has a financial cost. Further, line cleaning cannot be carried during 'opening hours' and has to be added-on to the already long working day. Overlain on top is the view (real or anecdotal) that reducing the frequency of cleaning from weekly to every two weeks has no perceived impact on product quality. Although perfectly reasonable, these views reflect a poor understanding of the role of line hygiene in assuring product quality. It can be argued that through better line hygiene, product quality would be improved, and that more consistent product quality would result in additional sales that would trivialise the significance of beer losses and inconvenience.

Although the focus of this section is (quite rightly) on line cleaning, it is also appropriate to consider the observations from the early work from the University of Birmingham and more recently VTT Biotechnology (Storgards & Haikara, 1996). Specifically with the emphasis on line cleaning, it is easy to lose sight of the importance of the beginning (keg coupler) or the tap-end of dispense. The cellar end of dispense is important but manageable inasmuch that the keg coupler and keg head can be easily sanitised. Further, the microbiological risk is minimised by the typically low temperature of the cellar together with the 'one touch' connection that is made between line and container. Conversely, from the perspective of risk management, the tap-end of dispense is a greater concern for at least three reasons. First, the tap is inevitably handled by bar staff; second, the environment is warm and aerobic; and, most damning of all, spouts and other removable bits of dispense 'plastic' are rarely cleaned properly. Unfortunately, the preferred option of soaking dispense 'plastics' in line cleaning detergent is rarely taken-up because the line cleaning fluid is typically kept in the cellar and not in the bar dispense area. Consequently, it is common practice to remove spouts and other dispense 'plastic' at the end of the night (or on line cleaning) and transfer to a glass of what is progressively 'beery' water. Although seemingly a good idea, such treatment exacerbates the microbiological contamination of removable spouts, sparklers and other dispense 'furniture'. The harsh reality is that steeping spouts, etc. in 'beery' water is akin to incubating these bits of dispense 'plastic' in a nutrient medium. Accordingly, contamination of dispense 'bits and pieces' is likely to get significantly worse rather than better! The risk requires to be managed, by simply soaking the 'plastics' in line cleaner on a regular (preferably daily) basis.

Over the years a number of publications have sought to quantify the size of microbiological contamination both across the dispense line and in the dispensed product. These reports have also demonstrated the impact of line cleaning on hygiene and, equally, the rapidity with which the system becomes recontaminated (see Hough et al., 1976; Harper et al., 1980; Storgards & Haikara, 1996). This work has without doubt raised the profile of dispense hygiene and contributed to the debate about best practice in controlling the risk. As noted by Storgards (1996), in the worst cases, these various reports describe alarmingly contamination as high as 105-107 cfu per ml of beer. However, these results are typically the 'first runnings' of the day (i.e. beer that has sat overnight in line) or after 250 ml (or so) has been removed. Either way whilst eloquently making the point, these results exaggerate the microbial loading, which, during normal dispense, would be anticipated to be much lower.

A hitherto unpublished study over a two-month period in 1998 monitored the loading of aerobic and anaerobic micro-organisms in lager dispensed from four taps in a busy, well-managed and successful bar. To overcome the 'first runnings' argument, 4 litres of product was pulled through each tap prior to sampling. Further, the sample was taken after the removal of the spout and sparkler, to ensure the recovered micro-organisms were exclusively associated with the beer line. Line cleaning was on a two-week cycle, typically on the Thursday of the second week. To gauge the impact of line cleaning on product microbiology, routine sampling was performed on the Thursday of the first week and the Wednesday and Friday of the second week. The raw microbiological data is presented in Fig. 8.28 and can be seen to be broadly cyclical in tandem with the cleaning cycle. It is noteworthy that the microbial loading was generally lowest from tap 1 and highest from tap 4 with occasional 'blips' in performance. Quantitatively, within a sample, there was little difference between the aerobic and anaerobic counts. The contribution of line cleaning to the microbiology of the product is readily apparent from the results reported in Table 8.14. These fascinating data clearly show that line cleaning reduces the microbial load of the dispensed product. However, these results suggest that line cleaning is of variable efficiency. For example, line cleaning reduced aerobes from 2 x 103 to 8 x 101 on one occasion whereas a month later the loading was reduced by only 30% (9 x 102 to 6 x 102). More detailed analysis of the 114 discrete results (anaerobes and aerobes on a tap-by-tap basis) (see Fig. 8.29) shows that the microbial loading was broadly in a band between 101 and 103 per ml of beer. The average of each data set showed aerobes and anaerobes to both be about 10 x 103ml 1 (pre-cleaning) and 2.6-3.1 x 102ml 1 (post-cleaning). As would be expected from such low microbial loads, there is no suggestion whatsoever that product quality was in anyway compromised. It is anticipated that these results will provide a useful benchmark for what is 'normal' in terms of dispensed product in the trade.

Fig. 8.28 Trade monitoring of the microbial loading ex-dispense - same brand dispensed from four taps (T = tap 1. aerobes. '2' = tap 1. anaerobes and so on); (unpublished results of Alisdair Hamilton. Wendy Box and David Quain).

Table 8.14 Microbiological loading of beer in the trade pre- and post-line cleaning (unpublished results of Alisdair Hamilton, Wendy Box and David Quain).

Before/after cleaning (date) Aerobes (cfu mf1) + sem Anaerobes (cfu mP1) + sem

Table 8.14 Microbiological loading of beer in the trade pre- and post-line cleaning (unpublished results of Alisdair Hamilton, Wendy Box and David Quain).

Before/after cleaning (date) Aerobes (cfu mf1) + sem Anaerobes (cfu mP1) + sem

Before (24/6)

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