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Silicon in Beer: Origin and Concentration
35 Silicon in Beer: Origin and Concentration Caroline Walker and Gary Freeman BRI, Lyttel Hall, Nutfield, Surrey, UK Ravin Jugdaohsingh MRC Human Nutrition Research, Elsie Widdowson Laboratory, Cambridge, UK Gastrointestinal Laboratory, The Rayne Institute (King’s College London), St. Thomas’ Hospital, London, UK Department of Nutrition, King’s College London, London, UK Jonathan J. Powell MRC Human Nutrition Research, Elsie Widdowson Laboratory, Cambridge, UK
Abstract
Introduction
There is increasing support for an important biological role of the trace element, silicon, in the optimal health of connective tissue, especially bone. Beer contains high levels of dietary silicon, in the well absorbed and biologically active form of orthosilicic acid [Si(OH)4]. It is widely accepted that barley, especially following malting and maceration, provides the major source of silicon within beer. However, how the different aspects of the brewing process then influence the final beer–silicon concentration is not known. Here we describe the findings of two previously unreported studies. First, we confirm that beer contains a high level (typically around 20 mg/l) of silicon. Secondly, from a pilot brewing trial, we show that barley is the major source of silicon in beer. Two different malts (malted barley) had distinctly different silicon concentrations, presumably because silicon levels of barley vary genetically. Silicon levels of the final product also depended on mashing and rinsing (sparging) conditions during the brewing process while filtration was also shown to affect (reduce) silicon levels of the beer, probably due to adsorption of orthosilicic acid onto material that is trapped by or that comprises the filter. Silicon levels of the water used for brewing are likely to have a small additional influence on the final beer–silicon levels, but in this particular work were negligible.
Silicon is an ubiquitous environmental element that is second only to oxygen in terms of elemental makeup of the earth’s crust. Nonetheless, the role of silicon in human biology and health remains enigmatic although there is increasing support for an important biological role of this trace element, when delivered in its orthosilicic acid form [Si(OH)4], in the optimal health of connective tissue, especially bone, skin and blood vessels. Interested readers are referred to a recent review by Sripanyakorn et al. (2005) as well as to the Chapter 80 in this book. Indeed, this latter chapter is relevant because of the realization that beer is a potentially rich dietary source of silicon in a form that can be well absorbed by humans into the bloodstream (Sripanyakorn et al., 2004). Although the source water in the brewing process is likely to contribute to the final beer–silicon content, it is widely accepted that barley, especially following malting and maceration, provides the major source of silicon within beer. However, how the different aspects of the brewing process influence the final beer–silicon concentration is not known. This chapter briefly presents the typical levels of silicon that are found within beers and then reports on an investigation into the unit operations within the brewing process by sampling the process streams at appropriate points for silicon analysis. Thus information has been gained on the inputs, losses and fractionation of silicon in the process. This work was undertaken by two of the authors (Walker and Freeman) at the pilot brewery of BRI and samples then analyzed as previously reported (Sripanyakorn et al., 2004) by Jugdaohsingh and Powell at St. Thomas’ Hospital. For solid or slurry samples, prior acid-assisted microwave digestion was undertaken.
List of Abbreviations FV KG PG PVPP RO XE5/XE200
Fermenter vessel Kieselguhr Present gravity Polyvinylpolypyrollidone Reverse osmosis Filtration sheets employed consecutively in filtration operation
Beer in Health and Disease Prevention ISBN: 978-0-12-373891-2
Copyright © 2009 Elsevier Inc. All rights of reproduction in any form reserved
368 Beer Composition and Properties
The Silicon Content of Alcoholic Beverages We previously reported a mean (SD) concentration of 19.2 6.6 mg Si/l beer from the analysis of 76 different beers (range: 9–39.4 mg/l; Sripanyakorn et al., 2004). Silicon concentration was not dependent on geographic origin, type of beer, alcohol content or the type of storage and packaging (Sripanyakorn et al., 2004). In contrast, levels of silicon in wines are more varied and although they can be as high as some beers in a recent small analysis (Powell et al., 2005), actual intakes of silicon in terms of servings are at least fivefold lower: 0.62–2.89 mg Si/serving wine (one glass or 125 ml) compared with 3.8–16.3 mg Si/serving for beers (300–574 ml) (Powell et al., 2005). Moreover, it is not clear what the chemical form of silicon is in wine as it may be added as a colloidal, insoluble form during fining (post-vinification). Such an addition is less common in beer, and therefore the silicon is usually only present as soluble orthosilicic acid (Sripanyakorn et al., 2004). Silicon levels in liquors/spirits are much lower being 1.3 0.04 mg/l ( Jugdaohsingh et al., 2004) and intake from these beverages are completely unimportant in terms of dietary silicon exposure. Table 35.1 shows analytical results for a small series of previously unreported beer, wine and spirit samples that were analyzed in a single batch with individual sample-based standards. These data emphasize the dominant role of beer in its potential to provide dietary silicon amongst the alcoholic beverages, especially given the likelihood that it is drunk in larger volumetric quantities.
Changes in Silicon Content Through the Brewing Process A pilot study was undertaken to investigate how the different aspects of the brewing process influences the final beer–silicon concentration. The process employed in the pilot brew (Figure 35.1) was typical of commercial brewing processes. Brewing water was tap water that had been through the process of reverse osmosis (RO). The malted barley was milled (ground). Barley varieties were “Pearl” as the standard brewing malt (87.5% by mass of the grist) and crystal malt, which is highly flavored (12.5%). This was then mixed with the hot brewing water (3 kg water to 1 kg malt) and maintained at 64°C for 60 min in a process known as mashing. The separation of liquid from spent grains, or “run-off,” involved raising the temperature to 78°C and draining the liquid (sweet wort). The spent grains were then rinsed with water at 78°C (sparging), until the bulked sweet wort volume was 86 l. Yeast (351 wet grams of Saccharomyces cerevisiae strain NCYC 1681) was then added and wort fermented for 6 days at 18°C. A 3-day maturation period at 13°C was employed, followed by cold maturation at 3°C for 1 day. Subsequently the settled yeast was
Table 35.1 The silicon content of beers, wines and spirits Silicon (mg/l) Alcoholic beverages
Mean
Range
N
Beers Can lager Can bitter Draft lager Draft bitter/mild
20.7 14.5 21.5 21.0
15.4–26.4 9.59–20.1 11.7–39.4 13.5–30.1
4 4 6 11
2.72–5.53 6.61–9.24 0.56–2.06 14.15–19.59
3 3 12 2
Ciders Wines (2 white; 1 red) Spirits Ports/sherry
3.70 7.67 1.26
Note: Silicon concentrations of different beers available in London (UK) in shops and/or pubs and, for comparison, silicon levels in spirits and wines are also shown. Silicon concentrations were determined by inductively coupled plasma optical emission spectrometry, from sample-based standards. N number of samples analyzed.
removed, followed by cold storage for a minimum of 7 days at 0°C. The beer sample was divided into two, and one sample was filtered through XE5/XE200 filter sheets and bottled. The other sample was filtered through kieselguhr at a dosage rate of 1 g/l. Samples of the bottled beer were processed separately through stabilizers, silica hydrogel (0.8 g/l) and polyvinylpolypyrollidone (PVPP) (0.5 g/l). Samples collected at the different stages of the brewing process were analyzed by inductively coupled plasma optical emission spectrometry as previously described (Sripanyakorn et al., 2004). Solid or slurry samples were prior digested by acid-assisted microwave digestion. The brewing process, and the points at which samples were taken for analysis, are shown in Figure 35.1 while the analytical results, and any specific observations (comment) on the sample at the time of analysis, are given in Table 35.2. Silicon ingress to the process from treated brewing water (liquor) was insignificant in these trials (Table 35.1). However, it should be noted that some water supplies have significant silicon content and the possibility should be considered that this passes pro rata through to the finished product. Regardless of the starting liquor silicon content, barley malt is an obvious major source of silicon in beer. Greater than 80% of silicon is in the cereal husks and absolute silicon levels vary between different varieties of barley, which appears to be at least partly genetically determined (Ma et al., 2003). This would translate into different silicon contents of the chosen malts (i.e. malted barley) used for brewing. For example, in this work (Table 35.2), standard ale malt contained 0.28 mg Si/g malt while crystal malt (a darker, toffee-tasting malt) contained 0.45 mg Si/g malt. Next we considered how silicon from the malted barley passed into solution and into the final product itself (beer). While the initial stirring of the malt in hot water, released
Silicon in Beer 369
Samples 22, 23 Malt grist
Heat recovery Syrup
Malt Cereal cleaning hopper Malt silo
Scale
Cereal cooker
Malt mill
Adjuncts mash
Malt
Samples 14,15 Wort kettle
Lauter tun
Mash vessel Mash
Sweet wort Spent grains discharge Sample 13
Samples 3, 4
Whirlpool
Sample 16
Wort Sample 17
Wort Cooler
Samples 5 –12
Sample 19 Surplus yeast
Deaerator Treated water
Surplus yeast discharge Chiller
Kegging line
Samples 38–41 48–50
Yeast storage
Chiller cross flow
Samples 32, 34, 35
Yeast Conditioning vessel
Bright beer tank
Blending
Stabilizer
Sterile air
Samples 20, 21, 24 –30
Wort
Yeast dosing
Fermenting vessel
Recovered beer
Bottling line
Yeast propagation
Wort aeration
Filter
CO2
Yeast
Yeast
Carbonation Sample 36
Beer chiller Samples 37, 47 Samples 31, 33
Green beer chiller
Figure 35.1 The brewing process and samples taken for analysis. Schematic of the brewing process used and the identification of the points at which sampling were undertaken (i.e. sample numbers) for silicon analysis as reported in Table 35.2.
approximately 10 mg Si/l, the first few rinses with very hot water released a further 10–60%, which, with continued rinsing, rapidly fell away as the washed husks were exhausted in terms of dissolvable sugar and silicon (Figure 35.2). Thus, it is clear that not only does the brewing process release silicon from the malted barley into solution but the rinsing process, that brewers use to recover sugar from the leftover husks, also results in increasing the silicon content of the beer. Nonetheless, in this work only 19% of the silicon in the malted barley was recovered into the beer. Fermentation had no effect on the silicon content of the beer (Figure 35.3), so the remaining silicon was left in the husks. It would be interesting to see how brewing techniques that grind the husks more finely could further affect how much silicon is released into the final product (presumably increased due to an increase in surface area of the husks). Interestingly, filtration reduced the beer–silicon content by one-third (Figure 35.3), in spite of the fact that orthosilicic acid (Si(OH)4), which is the form of silicon almost exclusively present in beer, is too small to be retained directly as a consequence of filtration. However, there is a possibility of the adsorption of silicon directly onto the filtration mat or indirectly onto material (e.g. yeast cells) trapped by the filtration mat. It should be
noted that some brewers also use silicon-containing filters but we found no loss of silicon from these into the beer. Many brands of beer are treated with process aids (materials that are employed in the brewing process that come into contact with the product, but have no function in the final product). These include kieselguhr (filtration aid, samples 33–35 in Table 35.2) and colloidal stabilizers such as silica hydrogel (samples 37–41) and PVPP (samples 47–50). The effect of these materials was measured on a laboratory pressure filter (a “Walton” filter). There was some evidence of adsorptive loss onto the PVPP but not the kieselguhr or silica hydrogel. In summary, the silicon content of the beer in this work was at the low end of that found in commercial samples, and this was only a single pilot study, but certain conclusions can still be drawn with confidence. The data clearly show that macerated barley is the predominant source of silicon in beer and that aspects of the brewing process including choice of malt, extent of grinding, maceration and rinsing, as well as filtration could impact upon silicon levels of the final product. These factors will vary between breweries causing the wide range of silicon content seen in commercial beers and explaining why geographical variation and the style/type of beer are not significant factors in determining beer–silicon content.
370 Beer Composition and Properties
Table 35.2 Silicon content of samples at the different points of the pilot brewing process Sample
Description
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Water post-RO Water post-burtonisation Mash at 5 min Mash end 1 h Sweet wort at 2 l run-off Sweet wort at 12 l run-off Sweet wort at 24 l run-off Sweet wort at 36 l run-off Sweet wort at 48 l run-off Sweet wort at 60 l run-off Sweet wort at 72 l run-off Sweet wort at 84 l run-off Spent grains Start boil (less than 5 min) after hop extract and syrup addition Boil end (55 min of 1 h boil) Whirlpool stand end (30 min) Trub ex-whirlpool Wort receiver after cutting Pitching yeast Fermentation day 2 Fermentation day 3 Pale ale malt Crystal malt Fermentation day 4 Fermentation day 5 Fermentation day 6 Fermentation day 7 Fermentation day 8 Fermentation day 9 Fermentation day 10 Pre-filter XE5/XE200 Post-filter XE5/XE200 Pre-KG filter Early run KG filtrate KG filtrate bulked Bottled beer Pre-silica gel Silica gel treated early run Silica gel mid-run Silica gel late run Silica gel treated bulked Walton filter control initial feed Control “filtrate” early run Control “filtrate” late run Control “filtrate” bulked Control feed end Pre-PVPP start Post-PVPP start Post-PVPP end Post-PVPP bulked
15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
Comments
Si concentration (mg/l)
mg Si/g of sample
0.046 0.060 27.248 17.194 PG 75.27, pH 5.26 PG 71.07, pH 5.24 PG 68.94, pH 5.21 PG 58.38, pH 5.20 PG 35.55, pH 5.20 PG 19.82, pH 5.22 PG 10.90, pH 5.22 PG 6.65, pH 5.25
10.034 9.831 11.413 16.170 13.034 10.475 7.661 6.646 305.850 9.500 7.366 7.401 7.740 5.037 87.873
Very wet: volume about 4.5 l PG in FV 38.4 PG 27.6 PG 22.2 BuhlerMiag milled 0.2 mm BuhlerMiag milled 0.2 mm PG 19.0 PG 14.4 PG 9.9 Warm rest 13°C Warm rest 13°C Warm rest 13°C Warm rest 13°C No PVPP No PVPP Dilution possible Pasteurized Should be as 36 Dilution possible
11.954 13.037 279.441 448.656 12.048 12.080 11.692 11.813 12.175 12.026 12.241 14.599 9.120 12.132 6.356 9.720 12.119 6.865 11.162 12.369 10.338 11.903 11.075 11.939 11.898 12.311 11.968 1.078 7.399 5.046
Note: Silicon concentration of samples taken at different points of the pilot brewing process (see Figure 35.1 for a schematic representation of the brewing process and points where the samples were collected). Collected samples were analyzed by inductively coupled plasma optical emission spectrometry as previously described (Sripanyakorn et al., 2004). Solid or slurry samples were prior digested by acid-assisted microwave digestion. Specific observations or measurements made on the sample during the brewing process are tabulated under comments. FV: fermenter vessel. KG: Kieselguhr, a filtration aid. PG: present gravity, measured in saccharin, equivalent to density (at 20°C, kg/m3) 1,000. PVPP: polyvinylpolypyrollidone, a colloidal stabilization agent. XE5, XE200: filtration sheets employed consecutively in filtration operation.
Silicon in Beer 371
●
80
16
70
14
60
12
50
10
40
8
30
6
⇑
4
20
2
10
0
●
Sugar (PG)
Silicon (mg/l)
Rinsing starts 18
0 2
12
24
36
48
60
72
84
●
●
Silicon levels of the final product also depend on mashing and rinsing conditions during the brewing process. Filtration may also affect (reduce) silicon levels of the beer due to adsorption onto material that is trapped by or comprises the filter. The process aid PVPP, which is employed as a colloidal stabilizer in some brands of beers, may remove some silicon by adsorption but further confirmatory trials should be performed. Silicon levels of the water used for brewing are likely to have a small additional influence on the final beer–silicon levels.
Rinse volume Si
Sugar
Acknowledgments
Figure 35.2 Release of silicon and sugars from the malt during rinsing. Silicon (Si) levels (mg/l) in solution as malted barley is stirred and rinsed with separate volumes of hot water. Sugar levels are also shown based on present gravity (PG; equivalent to density (at 20°C, kg/m3) 1,000). The individual rinses are combined with the liquor (sweet wort) collected prior to rinsing and the pooled sample then fermented.
14
Filtration
Silicon content (mg/l)
12 10 8 6 4 2 0 Before fermentation
After fermentation
Bottle
Figure 35.3 The effects of fermentation and filtration on silicon content of the beer. Silicon content (mg/l) of beer before fermentation, after fermentation and following filtration through XE5/XE200 filter sheets where a loss in soluble silicon is observed.
Summary Points ●
● ●
Beer contains a high level (typically around 20 mg/l) of soluble and absorbable dietary silicon. Barley is the major source of silicon in beer. Silicon levels of barley vary genetically and thus different malts (malted barley) have varying silicon contents.
The work was funded by the Institute and Guild of Brewers in the United Kingdom (now termed the Institute of Brewing and Distilling) and we are grateful for their support as well as the British Beer and Pub Association for their guidance. We also acknowledge Hazel Elliot for assistance with the analysis and other aspects of the studies.
References Jugdaohsingh, R., Tucker, K.L., Qiao, N., Cupples, L.A., Kiel, D.P. and Powell, J.J. (2004). J. Bone Miner. Res. 19, 297–307. Ma, J.F., Higashitani, A., Sato, K. and Takeda, K. (2003). Plant Soil. 249, 383–387. Powell, J.J., McNaughton, S.A., Jugdaohsingh, R., Anderson, S., Dear, J., Khot, F., Mowatt, L., Gleason, K.L., Sykes, M., Thompson, R.P.H., Bolton-Smith, C. and Hodson, M.J. (2005). Br. J. Nutr. 94, 804–812. Sripanyakorn, S., Jugdaohsingh, R., Elliott, H., Walker, C., Mehta, P., Shoukru, S., Thompson, R.P.H. and Powell, J.J. (2004). Br. J. Nutr. 91, 403–409. Sripanyakorn, S., Jugdaohsingh, R., Thompson, R.P.H. and Powell, J.J. (2005). Br. Nutr. Found. Nutr. Bull. 30, 222–230.
Abstract
Introduction
There is increasing support for an important biological role of the trace element, silicon, in the optimal health of connective tissue, especially bone. Beer contains high levels of dietary silicon, in the well absorbed and biologically active form of orthosilicic acid [Si(OH)4]. It is widely accepted that barley, especially following malting and maceration, provides the major source of silicon within beer. However, how the different aspects of the brewing process then influence the final beer–silicon concentration is not known. Here we describe the findings of two previously unreported studies. First, we confirm that beer contains a high level (typically around 20 mg/l) of silicon. Secondly, from a pilot brewing trial, we show that barley is the major source of silicon in beer. Two different malts (malted barley) had distinctly different silicon concentrations, presumably because silicon levels of barley vary genetically. Silicon levels of the final product also depended on mashing and rinsing (sparging) conditions during the brewing process while filtration was also shown to affect (reduce) silicon levels of the beer, probably due to adsorption of orthosilicic acid onto material that is trapped by or that comprises the filter. Silicon levels of the water used for brewing are likely to have a small additional influence on the final beer–silicon levels, but in this particular work were negligible.
Silicon is an ubiquitous environmental element that is second only to oxygen in terms of elemental makeup of the earth’s crust. Nonetheless, the role of silicon in human biology and health remains enigmatic although there is increasing support for an important biological role of this trace element, when delivered in its orthosilicic acid form [Si(OH)4], in the optimal health of connective tissue, especially bone, skin and blood vessels. Interested readers are referred to a recent review by Sripanyakorn et al. (2005) as well as to the Chapter 80 in this book. Indeed, this latter chapter is relevant because of the realization that beer is a potentially rich dietary source of silicon in a form that can be well absorbed by humans into the bloodstream (Sripanyakorn et al., 2004). Although the source water in the brewing process is likely to contribute to the final beer–silicon content, it is widely accepted that barley, especially following malting and maceration, provides the major source of silicon within beer. However, how the different aspects of the brewing process influence the final beer–silicon concentration is not known. This chapter briefly presents the typical levels of silicon that are found within beers and then reports on an investigation into the unit operations within the brewing process by sampling the process streams at appropriate points for silicon analysis. Thus information has been gained on the inputs, losses and fractionation of silicon in the process. This work was undertaken by two of the authors (Walker and Freeman) at the pilot brewery of BRI and samples then analyzed as previously reported (Sripanyakorn et al., 2004) by Jugdaohsingh and Powell at St. Thomas’ Hospital. For solid or slurry samples, prior acid-assisted microwave digestion was undertaken.
List of Abbreviations FV KG PG PVPP RO XE5/XE200
Fermenter vessel Kieselguhr Present gravity Polyvinylpolypyrollidone Reverse osmosis Filtration sheets employed consecutively in filtration operation
Beer in Health and Disease Prevention ISBN: 978-0-12-373891-2
Copyright © 2009 Elsevier Inc. All rights of reproduction in any form reserved
368 Beer Composition and Properties
The Silicon Content of Alcoholic Beverages We previously reported a mean (SD) concentration of 19.2 6.6 mg Si/l beer from the analysis of 76 different beers (range: 9–39.4 mg/l; Sripanyakorn et al., 2004). Silicon concentration was not dependent on geographic origin, type of beer, alcohol content or the type of storage and packaging (Sripanyakorn et al., 2004). In contrast, levels of silicon in wines are more varied and although they can be as high as some beers in a recent small analysis (Powell et al., 2005), actual intakes of silicon in terms of servings are at least fivefold lower: 0.62–2.89 mg Si/serving wine (one glass or 125 ml) compared with 3.8–16.3 mg Si/serving for beers (300–574 ml) (Powell et al., 2005). Moreover, it is not clear what the chemical form of silicon is in wine as it may be added as a colloidal, insoluble form during fining (post-vinification). Such an addition is less common in beer, and therefore the silicon is usually only present as soluble orthosilicic acid (Sripanyakorn et al., 2004). Silicon levels in liquors/spirits are much lower being 1.3 0.04 mg/l ( Jugdaohsingh et al., 2004) and intake from these beverages are completely unimportant in terms of dietary silicon exposure. Table 35.1 shows analytical results for a small series of previously unreported beer, wine and spirit samples that were analyzed in a single batch with individual sample-based standards. These data emphasize the dominant role of beer in its potential to provide dietary silicon amongst the alcoholic beverages, especially given the likelihood that it is drunk in larger volumetric quantities.
Changes in Silicon Content Through the Brewing Process A pilot study was undertaken to investigate how the different aspects of the brewing process influences the final beer–silicon concentration. The process employed in the pilot brew (Figure 35.1) was typical of commercial brewing processes. Brewing water was tap water that had been through the process of reverse osmosis (RO). The malted barley was milled (ground). Barley varieties were “Pearl” as the standard brewing malt (87.5% by mass of the grist) and crystal malt, which is highly flavored (12.5%). This was then mixed with the hot brewing water (3 kg water to 1 kg malt) and maintained at 64°C for 60 min in a process known as mashing. The separation of liquid from spent grains, or “run-off,” involved raising the temperature to 78°C and draining the liquid (sweet wort). The spent grains were then rinsed with water at 78°C (sparging), until the bulked sweet wort volume was 86 l. Yeast (351 wet grams of Saccharomyces cerevisiae strain NCYC 1681) was then added and wort fermented for 6 days at 18°C. A 3-day maturation period at 13°C was employed, followed by cold maturation at 3°C for 1 day. Subsequently the settled yeast was
Table 35.1 The silicon content of beers, wines and spirits Silicon (mg/l) Alcoholic beverages
Mean
Range
N
Beers Can lager Can bitter Draft lager Draft bitter/mild
20.7 14.5 21.5 21.0
15.4–26.4 9.59–20.1 11.7–39.4 13.5–30.1
4 4 6 11
2.72–5.53 6.61–9.24 0.56–2.06 14.15–19.59
3 3 12 2
Ciders Wines (2 white; 1 red) Spirits Ports/sherry
3.70 7.67 1.26
Note: Silicon concentrations of different beers available in London (UK) in shops and/or pubs and, for comparison, silicon levels in spirits and wines are also shown. Silicon concentrations were determined by inductively coupled plasma optical emission spectrometry, from sample-based standards. N number of samples analyzed.
removed, followed by cold storage for a minimum of 7 days at 0°C. The beer sample was divided into two, and one sample was filtered through XE5/XE200 filter sheets and bottled. The other sample was filtered through kieselguhr at a dosage rate of 1 g/l. Samples of the bottled beer were processed separately through stabilizers, silica hydrogel (0.8 g/l) and polyvinylpolypyrollidone (PVPP) (0.5 g/l). Samples collected at the different stages of the brewing process were analyzed by inductively coupled plasma optical emission spectrometry as previously described (Sripanyakorn et al., 2004). Solid or slurry samples were prior digested by acid-assisted microwave digestion. The brewing process, and the points at which samples were taken for analysis, are shown in Figure 35.1 while the analytical results, and any specific observations (comment) on the sample at the time of analysis, are given in Table 35.2. Silicon ingress to the process from treated brewing water (liquor) was insignificant in these trials (Table 35.1). However, it should be noted that some water supplies have significant silicon content and the possibility should be considered that this passes pro rata through to the finished product. Regardless of the starting liquor silicon content, barley malt is an obvious major source of silicon in beer. Greater than 80% of silicon is in the cereal husks and absolute silicon levels vary between different varieties of barley, which appears to be at least partly genetically determined (Ma et al., 2003). This would translate into different silicon contents of the chosen malts (i.e. malted barley) used for brewing. For example, in this work (Table 35.2), standard ale malt contained 0.28 mg Si/g malt while crystal malt (a darker, toffee-tasting malt) contained 0.45 mg Si/g malt. Next we considered how silicon from the malted barley passed into solution and into the final product itself (beer). While the initial stirring of the malt in hot water, released
Silicon in Beer 369
Samples 22, 23 Malt grist
Heat recovery Syrup
Malt Cereal cleaning hopper Malt silo
Scale
Cereal cooker
Malt mill
Adjuncts mash
Malt
Samples 14,15 Wort kettle
Lauter tun
Mash vessel Mash
Sweet wort Spent grains discharge Sample 13
Samples 3, 4
Whirlpool
Sample 16
Wort Sample 17
Wort Cooler
Samples 5 –12
Sample 19 Surplus yeast
Deaerator Treated water
Surplus yeast discharge Chiller
Kegging line
Samples 38–41 48–50
Yeast storage
Chiller cross flow
Samples 32, 34, 35
Yeast Conditioning vessel
Bright beer tank
Blending
Stabilizer
Sterile air
Samples 20, 21, 24 –30
Wort
Yeast dosing
Fermenting vessel
Recovered beer
Bottling line
Yeast propagation
Wort aeration
Filter
CO2
Yeast
Yeast
Carbonation Sample 36
Beer chiller Samples 37, 47 Samples 31, 33
Green beer chiller
Figure 35.1 The brewing process and samples taken for analysis. Schematic of the brewing process used and the identification of the points at which sampling were undertaken (i.e. sample numbers) for silicon analysis as reported in Table 35.2.
approximately 10 mg Si/l, the first few rinses with very hot water released a further 10–60%, which, with continued rinsing, rapidly fell away as the washed husks were exhausted in terms of dissolvable sugar and silicon (Figure 35.2). Thus, it is clear that not only does the brewing process release silicon from the malted barley into solution but the rinsing process, that brewers use to recover sugar from the leftover husks, also results in increasing the silicon content of the beer. Nonetheless, in this work only 19% of the silicon in the malted barley was recovered into the beer. Fermentation had no effect on the silicon content of the beer (Figure 35.3), so the remaining silicon was left in the husks. It would be interesting to see how brewing techniques that grind the husks more finely could further affect how much silicon is released into the final product (presumably increased due to an increase in surface area of the husks). Interestingly, filtration reduced the beer–silicon content by one-third (Figure 35.3), in spite of the fact that orthosilicic acid (Si(OH)4), which is the form of silicon almost exclusively present in beer, is too small to be retained directly as a consequence of filtration. However, there is a possibility of the adsorption of silicon directly onto the filtration mat or indirectly onto material (e.g. yeast cells) trapped by the filtration mat. It should be
noted that some brewers also use silicon-containing filters but we found no loss of silicon from these into the beer. Many brands of beer are treated with process aids (materials that are employed in the brewing process that come into contact with the product, but have no function in the final product). These include kieselguhr (filtration aid, samples 33–35 in Table 35.2) and colloidal stabilizers such as silica hydrogel (samples 37–41) and PVPP (samples 47–50). The effect of these materials was measured on a laboratory pressure filter (a “Walton” filter). There was some evidence of adsorptive loss onto the PVPP but not the kieselguhr or silica hydrogel. In summary, the silicon content of the beer in this work was at the low end of that found in commercial samples, and this was only a single pilot study, but certain conclusions can still be drawn with confidence. The data clearly show that macerated barley is the predominant source of silicon in beer and that aspects of the brewing process including choice of malt, extent of grinding, maceration and rinsing, as well as filtration could impact upon silicon levels of the final product. These factors will vary between breweries causing the wide range of silicon content seen in commercial beers and explaining why geographical variation and the style/type of beer are not significant factors in determining beer–silicon content.
370 Beer Composition and Properties
Table 35.2 Silicon content of samples at the different points of the pilot brewing process Sample
Description
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Water post-RO Water post-burtonisation Mash at 5 min Mash end 1 h Sweet wort at 2 l run-off Sweet wort at 12 l run-off Sweet wort at 24 l run-off Sweet wort at 36 l run-off Sweet wort at 48 l run-off Sweet wort at 60 l run-off Sweet wort at 72 l run-off Sweet wort at 84 l run-off Spent grains Start boil (less than 5 min) after hop extract and syrup addition Boil end (55 min of 1 h boil) Whirlpool stand end (30 min) Trub ex-whirlpool Wort receiver after cutting Pitching yeast Fermentation day 2 Fermentation day 3 Pale ale malt Crystal malt Fermentation day 4 Fermentation day 5 Fermentation day 6 Fermentation day 7 Fermentation day 8 Fermentation day 9 Fermentation day 10 Pre-filter XE5/XE200 Post-filter XE5/XE200 Pre-KG filter Early run KG filtrate KG filtrate bulked Bottled beer Pre-silica gel Silica gel treated early run Silica gel mid-run Silica gel late run Silica gel treated bulked Walton filter control initial feed Control “filtrate” early run Control “filtrate” late run Control “filtrate” bulked Control feed end Pre-PVPP start Post-PVPP start Post-PVPP end Post-PVPP bulked
15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
Comments
Si concentration (mg/l)
mg Si/g of sample
0.046 0.060 27.248 17.194 PG 75.27, pH 5.26 PG 71.07, pH 5.24 PG 68.94, pH 5.21 PG 58.38, pH 5.20 PG 35.55, pH 5.20 PG 19.82, pH 5.22 PG 10.90, pH 5.22 PG 6.65, pH 5.25
10.034 9.831 11.413 16.170 13.034 10.475 7.661 6.646 305.850 9.500 7.366 7.401 7.740 5.037 87.873
Very wet: volume about 4.5 l PG in FV 38.4 PG 27.6 PG 22.2 BuhlerMiag milled 0.2 mm BuhlerMiag milled 0.2 mm PG 19.0 PG 14.4 PG 9.9 Warm rest 13°C Warm rest 13°C Warm rest 13°C Warm rest 13°C No PVPP No PVPP Dilution possible Pasteurized Should be as 36 Dilution possible
11.954 13.037 279.441 448.656 12.048 12.080 11.692 11.813 12.175 12.026 12.241 14.599 9.120 12.132 6.356 9.720 12.119 6.865 11.162 12.369 10.338 11.903 11.075 11.939 11.898 12.311 11.968 1.078 7.399 5.046
Note: Silicon concentration of samples taken at different points of the pilot brewing process (see Figure 35.1 for a schematic representation of the brewing process and points where the samples were collected). Collected samples were analyzed by inductively coupled plasma optical emission spectrometry as previously described (Sripanyakorn et al., 2004). Solid or slurry samples were prior digested by acid-assisted microwave digestion. Specific observations or measurements made on the sample during the brewing process are tabulated under comments. FV: fermenter vessel. KG: Kieselguhr, a filtration aid. PG: present gravity, measured in saccharin, equivalent to density (at 20°C, kg/m3) 1,000. PVPP: polyvinylpolypyrollidone, a colloidal stabilization agent. XE5, XE200: filtration sheets employed consecutively in filtration operation.
Silicon in Beer 371
●
80
16
70
14
60
12
50
10
40
8
30
6
⇑
4
20
2
10
0
●
Sugar (PG)
Silicon (mg/l)
Rinsing starts 18
0 2
12
24
36
48
60
72
84
●
●
Silicon levels of the final product also depend on mashing and rinsing conditions during the brewing process. Filtration may also affect (reduce) silicon levels of the beer due to adsorption onto material that is trapped by or comprises the filter. The process aid PVPP, which is employed as a colloidal stabilizer in some brands of beers, may remove some silicon by adsorption but further confirmatory trials should be performed. Silicon levels of the water used for brewing are likely to have a small additional influence on the final beer–silicon levels.
Rinse volume Si
Sugar
Acknowledgments
Figure 35.2 Release of silicon and sugars from the malt during rinsing. Silicon (Si) levels (mg/l) in solution as malted barley is stirred and rinsed with separate volumes of hot water. Sugar levels are also shown based on present gravity (PG; equivalent to density (at 20°C, kg/m3) 1,000). The individual rinses are combined with the liquor (sweet wort) collected prior to rinsing and the pooled sample then fermented.
14
Filtration
Silicon content (mg/l)
12 10 8 6 4 2 0 Before fermentation
After fermentation
Bottle
Figure 35.3 The effects of fermentation and filtration on silicon content of the beer. Silicon content (mg/l) of beer before fermentation, after fermentation and following filtration through XE5/XE200 filter sheets where a loss in soluble silicon is observed.
Summary Points ●
● ●
Beer contains a high level (typically around 20 mg/l) of soluble and absorbable dietary silicon. Barley is the major source of silicon in beer. Silicon levels of barley vary genetically and thus different malts (malted barley) have varying silicon contents.
The work was funded by the Institute and Guild of Brewers in the United Kingdom (now termed the Institute of Brewing and Distilling) and we are grateful for their support as well as the British Beer and Pub Association for their guidance. We also acknowledge Hazel Elliot for assistance with the analysis and other aspects of the studies.
References Jugdaohsingh, R., Tucker, K.L., Qiao, N., Cupples, L.A., Kiel, D.P. and Powell, J.J. (2004). J. Bone Miner. Res. 19, 297–307. Ma, J.F., Higashitani, A., Sato, K. and Takeda, K. (2003). Plant Soil. 249, 383–387. Powell, J.J., McNaughton, S.A., Jugdaohsingh, R., Anderson, S., Dear, J., Khot, F., Mowatt, L., Gleason, K.L., Sykes, M., Thompson, R.P.H., Bolton-Smith, C. and Hodson, M.J. (2005). Br. J. Nutr. 94, 804–812. Sripanyakorn, S., Jugdaohsingh, R., Elliott, H., Walker, C., Mehta, P., Shoukru, S., Thompson, R.P.H. and Powell, J.J. (2004). Br. J. Nutr. 91, 403–409. Sripanyakorn, S., Jugdaohsingh, R., Thompson, R.P.H. and Powell, J.J. (2005). Br. Nutr. Found. Nutr. Bull. 30, 222–230.