Rotary jet head a device for accelerating the fermentation process in brewing

Transcription

1 Research article Received: 16 November 215 Revised: 27 January 216 Accepted: 2 March 216 Published online in Wiley Online Library: 15 April 216 (wileyonlinelibrary.com) DOI 1.12/jib.32 Rotary jet head a device for accelerating the fermentation process in brewing Marek Zdaniewicz, 1 *AleksanderPoreda 1 and Tadeusz Tuszyński 2 The world beer market is dominated by lagers, with production estimated at hundreds of millions of hectolitres per year. The vast majority of the beer is produced using CCT (cylindro-conical tank) technology. Fermentation and maturation are time-consuming processes and the bottlenecks of beer production. A rotary jet head () a device originally used as a cleaning device is proposed for use as a tool to provide homogeneity in the tank and to increase the activity of the yeast cells by keeping them in suspension during the fermentation process. The main objective of the study was to analyse the impact of mixing the content of the fermentation tank (by the means of an ) on the time of fermentation, maturation and cooling. The experiments were carried out under full industrial operational conditions. It was concluded that mechanical mixing, in a CCT of 38 hl, shortened the time of lager beer production process by ca. 15%, the time of fermentation by ca. 24 h and the cooling time by ca. 35 h. Copyright 216 The Keywords: CCT; cooling; fermentation; rotary jet head; maturation; mixing Introduction The expansion of a brewery is an expensive way to increase capacity production, so brewers search for less expensive solutions, such as introducing new technologies or/and improving the existing processes, to achieve this goal (1). From the nineteenth century on, a lot of attention has been paid to the bottlenecks in brewhouse processing. Consequently, there have been many innovations that have increased the capacity of the brewhouse and improved the economic indicators (2). Fermentation and maturation are other processes that could be improved. In many breweries, CCT (cylindro-conical tank) technology has been successfully applied to replace the traditional (open) fermenters and lagering tanks (3). This solution (CCT) designed by Nathan (4) at the beginning of the twentieth century has not been significantly modified since that time (5,6). Boulton et al.(7) showed that, in CCT, the yeast cells begin to sediment about 5 h after the start of the process (when the attenuation is often <6%). Furthermore, after 8 9 h, >9% of the living yeast cells are found in the cone of the fermenter. Consequently, additional mixing in the CCT is desirable to improve fermentation and thereby the efficiency of the process. Mixing is a commonly used process in households, in construction and in the manufacture of chemicals, foods and pharmaceuticals, as well as in other areas of life (8). Inthefoodindustry,the mixing of liquids, solids, and gases is one of the most frequent production activities (9,1). Mixing in a CCT ensures better access for yeast cells to the nutrients in the fermenting wort, increases the intensity of mass transfer and eliminates/reduces the differences in the concentration of biomass or temperature within the tank (11). Mixing also inhibits the sedimentation process and leads to a better distribution of yeast cells within the tank. It has been proven in both laboratory (12,13) and in medium-sized industrial trials ca. 15 hl (14) that agitation intensifies the process and improves the reproducibility and predictability of the fermentation. Intensification of processes is a key action to improve the economic situation of breweries by increasing production capacity, without an expansion of the existing plant. Until now the introduction of mechanical agitation in the brewing industry was limited owing to the fear of damage to yeast cells, formation of shear forces and microbiological contamination (12,15). A rotary jet head () is a mixing device that may solve the problem of heterogeneity in a CCT, without increasing the microbiological risks (its original role was to keep the tank clean and microbiologically safe). The has been long used in the chemical and food industries (including beer and other beverages) to ensure fast and efficient cleaning of tanks (16). The aim of the research was to fill the gap in knowledge by providing results from experiments using in a large-scale production process. The was installed in the full industry scale tanks (38 hl) and its influence evaluated on the time of each stage of fermentation, maturation and cooling. The effect of mixing on the process was determined in respect to savings in time and the possibility of increasing the fermentation tank throughput. Materials and methods Experimental design The experiment was conducted under full-scale conditions. The was installed in a CCT (total capacity 38 hl, working capacity ca. 32 hl). The producer (Alfa Laval, Denmark) recommends the * Correspondence to: Marek Zdaniewicz, Department of Fermentation Technology and Technical Microbiology, University of Agriculture in Krakow, Krakow, Poland. m.zdaniewicz@ur.krakow.pl 1 Department of Fermentation Technology and Technical Microbiology, University of Agriculture in Krakow, Krakow, Poland 2 Department of Chemistry and Food Toxicology, University of Rzeszow, Rzeszow, Poland 317 J. Inst. Brew. 216; 122: Copyright 216 The

2 M. Zdaniewicz et al. Figure 1. Rotary jet head installation: (A) recommended by the producer; (B) installation adapted to the requirements of the study (source: Alfa Laval materials). 318 mounting of a supply pipe from the top of the tank (Fig. 1A), while in these experiment the pipeline with a was introduced into the vessel through the conical part of the tank (Fig. 1B), in order to save the pipeline cost. The was placed at a height of approximately 3.5 m from the base of the cone. During fermentation, maturation and conditioning, the pump was working at a frequency of 4Hz, corresponding to a flow rate of 29 hl/h at a pressure of about 6.4 bar (excluding the 24 h before yeast cropping when the pump was switched off to allow yeast sedimentation). Materials Worts. All-malt wort was produced in batches of 1 hl. Each of the tanks, the tank and the control tank (), was filled with three batches of wort. Yeasts. Yeast of the third generation (Saccharomyces carlsbergensis, W34/7) was used for the fermentations, with a viable cell pitching rate of /ml. Fermentation conditions. The process in the tank was compared with the control (a fermentation tank of the same construction, cooling system and distance from the refrigerant ammonia station). Each tank was equipped with three temperature sensors located at different heights of the tank in order to adequately control the process parameters (Fig. 1). The fermentation (1 C), maturation (14.5 C) and cold conditioning (.7 C) processes took about 18 days in total. The initial wort extract was 15 P. A small pump was installed in each tank for the purpose of sampling during production. Analytical methods Extract. The extract ( P) was measured by the automatic wort and beer analyser (Alcolyzer, Anton Paar DMA 45+). A sample (5 ml) of fermenting wort was mixed with ~4 g of diatomaceous earth and filtered through paper filter to obtain ~3 ml of filtrate. The filtrate was degassed for 2 min (universal shaker, 15 rpm), adjusted to 2 C and filtered again. Vicinal diketones. Vicinal diketones (μg/l) were measured with the use of a gas chromatograph, GC Fisons Instruments 8, CP-Sil8CB (l =6m;d =.53mm;f =1μm),withanFIDdetector and an autosampler HS 8. The filtrate (2.5 ml) was maintained at 4 C for 4 min (head space method) and used for analysis with an internal standard, 2,3-hexadione. Reproducibility Results are presented as the average of six or more independent experiments with the bars representing the standard deviation. Data were analysed by one-way analysis of variance (ANOVA) to test the significance of main effect of the mixing. The significance of difference for each parameter was analysed separately, using Duncan s Multiple Range test (Statistica v. 1, StatSoft Inc.). Results and discussion Fermentation time To assess the influence of on the fermentation rate, the extract content in wort was measured daily, to assess the time needed to obtain the desired apparent attenuation (ca. 2.8 P). Figure 2 shows the drop in the apparent extract during the fermentation performed with and without the. The fermentation time was shortened by ~24 h in trials with mixing, as compared with the control. As a result of use of the, yeast cells were kept in suspension, thus ensuring better availability of wort nutrients, leading to a more efficient fermentation. At the beginning of the process (from day to 4), there was no significant difference between the two trials. The apparent wileyonlinelibrary.com/journal/jib Copyright 216 The J. Inst. Brew. 216; 122:

3 Rotary jet head - accelerating fermentation process Apparent extract [ P] Figure 2. Apparent extract of wort during fermentation with mixing () and without mixing () (n 6; mean ± standard deviation). extract dropped in both samples from 15 to 8.4 P (day 4). The significant difference in the extract drop was observed from day 5 to day 8. Consequently, the desired attenuation (ca. 2.8 P) was obtained after 7 () and 8 (control) days. The improvement of fermentation speed owing to mixing was also observed by Boswell et al. (12). Using 5 ml flasks, they obtained a reduction of time of about 68 h (from the start of the process to achieving the final attenuation), depending upon the intensity of mixing conducted. In other work it was reported that mechanical mixing shortened the time of fermentation by about 36 h in 15 hl CCT fermenters (7). Nienow et al. (11) reported a 24 h reduction of fermentation time in Munton s Pale Ale and Grolsch lager beer, fermented in 5 L fermenters. Based on published works, it can be assumed that the use of mixing prevents premature yeast sedimentation, as suggested by Boulton (14) and consequently decreases the time of the fermentation process. The decreased rate of fermentation observed in the control trial (from day 5) was in an agreement with Boulton(14), who reported that, when no mixing was applied 4 days after pitching, 9% of the live yeast cells had sedimented and remained in the bottom part of the tank. Maturation time Diacetyl and 2,3-pentadione (VDK, vicinal diketones) are undesired components in beer (17). Their low sensory detection threshold and negative impact on the flavour of beer make the concentration of VDK the most common indicator of beer maturation (18,19). The VDK thresholds (μg/l) are ~15 for diacetyl and ~9 for 2,3-pentadione (2). Thus brewers aim at achieving their content below those values. When the VDK level is above this limit, Diacetyl [µg/l] Figure 3. Diacetyl content with () or without () mixing (n 6; mean ± standard deviation). 319 J. Inst. Brew. 216; 122: Copyright 216 The wileyonlinelibrary.com/journal/jib

4 M. Zdaniewicz et al ,3-pentadione [µg/l] Figure 4. The 2,3-pentadione content with () or without () mixing (n 6; mean ± standard deviation). the beer is not transferred to filtration in the brewery used for this investigation. Figures 3 and 4 show the concentration of diacetyl and 2,3- pentadione measured during fermentation of wort. Agitation did not influence the time of formation or the reduction of diacetyl and 2,3-pentadione. According to the brewery procedures, maturation is considered to be complete when the level of the VDK compounds (sum of diacetyl and 2,3- pentadione) is <8 μg/l. The formation of the VDK compounds had already started on the first day of fermentation and continued for ~5 days, to a maximum content of VDK (μg/l) ~37 for the test fermentation and ~34 for the control fermentation. A VDK reduction of <8 μg/l was obtained in both series of trials in day 1. There are some publications related to the formation and reduction of VDK compounds during mechanical mixed fermentation and maturation. Boulton (5) showed that, in some cases, it was possible to reduce the maturation time by about 15 3%, but this was not confirmed in the present study. This could be due to the 24 h interval collection of samples, which made it difficult to identify potential savings of <24 h. Cooling time When the desired VDK level was achieved, the yeast biomass was cropped from the tank. About 24 h after the yeast cropping process, the cooling was activated in both tanks. Figure 5 shows the time needed to obtain the temperature of.7 C. The use of the significantly reduced the time required to obtain this desired temperature. In trials, the cooling was completed after 51 h, Cooling time [h] Figure 5. The cooling time required to obtain.7 C with and without mixing (n 6; mean ± standard deviation). wileyonlinelibrary.com/journal/jib Copyright 216 The J. Inst. Brew. 216; 122:

5 321 Rotary jet head - accelerating fermentation process while in the control tank the time needed to the end of cooling was ca. 86 h (ca. 5% longer than in the process). The temperature of the beer was lowered to.7 C and maintained for 24 h to allow the yeast cells to sediment in the conical part of CCT. According to Miedl and Bamforth (21), a short storage at a temperature < C is better for physico-chemical beer stability than a longer lagering at C, or at higher temperatures. In that respect, the use of a could indirectly improve the quality of the produced beer by significantly shortening the cooling time. In the control trials (labelled ), the heat exchange was only supported by convection processes caused by natural flow of the chilled beer. It has been shown in other studies that density changes are not linear in the range of low temperatures. The maximum density of beer is obtained at a temperature of ~3 C, and further cooling causes a reduction in density (22). During the experiments, the beer was cooled with the use of cooling jackets. Although the natural movement of the beer leads to the set temperature, the process was very slow and lasted for ~86 h for the control beer. The use of the changed the fluid movements and turbulence inside the tank, causing a significant reduction in time of ~35 h to reach the temperature.7 C. Summary and conclusions One of the most important findings of this research was the significant reduction in beer production time, achieved by the application of a in the CCT. The mechanical mixing shortened the time of fermentation process by ca. 24 h, having no or little influence on maturation time. The cooling stage could be accelerated by ca. 35 h by the. The positive effect of the on the time of beer production could enable prolonged cold conditioning (beer quality improvement) and a shortening of the total beer production by ca. 15% (brewery efficiency improvement). 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