An In-depth Review of Beer Production with
Problem Solving Strategies
Werner Back, Martina Gastl, Martin Krottenthaler,
Ludwig Narziß, Martin Zarnkow
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Cover: Christina Schönberger
Translation: McGreger Translations, Freising, Germany
Layout and typesetting: Komhus Agentur für Kommunikation, Essen, Germany;
Communicate Design and Language, Mülheim an der Ruhr, Germany
There has been a desire within the international brewing community for some time to make this technical text available in English, and with the present translation of ‘Brewing Techniques in Practice’ this has finally been realized. In doing so, information concerning beer styles and brewing methods commonplace outside of Germany has been incorporated into this volume. Craft beer has also been taken into consideration. The existing chapters were revised and updated to reflect the current state of scientific findings and technical knowledge. Like the original text, the English edition has been organized along thematic lines, which address routine day-to-day tasks faced by brewing technologists.
The complex explanations found in this book provide a well-reasoned, articulate and comprehensive overview of each topic for brewers working in the industry as well as for students of brewing. The respective concepts are clearly elucidated in their entirety in each chapter, both at a scientific and a technical level. Particular emphasis is placed on the fundamental aspects of biochemical processes as well as production techniques, so that the information can be readily applied in practice. The organization of the book, which includes a thorough summary at the end of each chapter, has proven to be an indispensable tool, especially as it allows problems, causes and solutions to be explored with ease. Those in the industry will find the tables with standard values for substances typically found in wort and beer to be quite useful. A table has been added providing conversions of international units along with key indicators for technical processes. An overview of the requirements necessary for a beer to be acknowledged as having been "brewed according to the German Reinheitsgebot" has likewise been appended to this English edition.
Additionally, a section of the book has been set aside for the purpose of distinguishing the Reinheitsgebot (referred only to lager beer), the medieval purity law of 1516, from the current provisional beer law (Vorläufiges Biergesetz), which comprises the current regulations governing beer production in Germany. The Reinheitsgebot still serves as the core of the Vorläufiges Biergesetz, in that the four ingredients stipulated for brewing beer in the law from 1516 still apply under the existing regulations. The Vorläufiges Biergesetz regulates all further aspects of modern beer production.
I am grateful to my co-authors for their contributions to the current English edition, as well as to my former colleagues at the Technologie der Brauerei I at the TUM-Weihenstephan, who laid the groundwork for this technical brewing text. I owe all of them a debt of gratitude for their diligent and competent teamwork.
My thanks also go to the Fachverlag Hans Carl for the willingness to publish this revised and updated English edition of the handbook.
Werner Back
Freising, August 2019
Werner Back (editor)
Ingrid Bohak (†)
Felix Burberg
Torsten Dickel
Oliver Franz
Martina Gastl
Stefan Hanke
Klaus Hartmann
Markus Herrmann
Dietmar Kaltner
Matthias Keßler
Stefan Kreisz
Martin Krottenthaler
Florian Kühbeck
Ralf Mezger
Ludwig Narziß
Mark Schneeberger
Christina Schönberger
Cem Schwarz
Elmar Spieleder
Frithjof Thiele
Kornel Vetterlein
Sascha Wunderlich
Michael Wurzbacher
Martin Zarnkow
Joachim Zürcher
MALT
1Introduction
2The Quality Attributes of Barley Malt and Wheat Malt
2.1Quality attributes of barley malt
2.1.1Cytolysis
2.1.2Proteolysis
2.1.3Amylolysis
2.1.4Additional malt specifications
2.1.4.1DMS precursor
2.1.4.2TBI (thiobarbituric acid index)
2.1.4.3Malt color and boiled wort color
2.1.4.4pH
2.2Quality criteria for wheat malt
2.2.1Cytolysis
2.2.2Proteolysis
2.2.3Amylolysis
2.3Food Safety
3Summary
4Overview
5References
HOPS
1Introduction
1.1Valuable compounds in hops
1.1.1Bitter acids
1.1.2Aroma compounds
1.1.3Polyphenols
1.1.4Analytical characterization of commonly encountered hop varieties
1.2Hop products
1.3Analysis methods
2Special Aspects of Hops in Brewing Applications
2.1Hop addition
2.1.1Beer produced with a low hopping rate
2.1.2Beer produced with a high hop rate
2.1.3Beer with a pronounced hop aroma
2.1.4Beer enriched with xanthohumol
2.1.5Adding hops on the cold side of production
2.1.6Lightstruck flavor
2.2Hop utilization
2.3Foam
2.4Microbiology
2.5Addition of downstream hop products
2.6Storing hops
3Summary
4Overview
5References
MASHING
1Introduction
2The Technology of Mashing
2.1Mash parameters
2.2Selected mash programs
2.2.1Spring mash program
2.2.2Separating the mash to achieve β-Glucan degradation
2.2.3The maltase mashing method
2.2.4Dark beer styles
3Summary
4Overview
5References
WORT BOILING AND WORT BOILING SYSTEMS
1Introduction
2The Technological Basis for Wort Boiling
2.1Maintaining the heated wort at a constant temperature
2.2Evaporation
2.2.1Evaporative efficiency [3]
2.2.2Pre-cooling the wort
2.2.3Downstream evaporation
2.3Interplay between key analytical metrics for wort boiling
2.4Modern wort boiling systems
2.4.1Internal wort boiling systems
2.4.2External wort boiling systems
2.4.3High-temperature wort boiling
2.4.4Dynamic wort boiling slightly above atmospheric pressure
2.4.5Gentle boiling with SchoKo
2.4.6Wort stripping
2.4.7Vacuum evaporation
2.4.8Flash evaporation with Varioboil
2.4.9The Merlin® thin film evaporator
2.4.10The Jetstar internal calandria
2.4.11The Stromboli internal calandria
2.4.12Break material
2.4.12.1Hot break material
2.4.12.2Cold break material
2.4.13Vapor condensate
3Summary
4Overview
5References
ACIDIFICATION WITH NATURAL LACTIC ACID
1Introduction
2Techniques Used in the Production of Sauergut
2.1Lactic acid cultures
2.2The advantages of using natural lactic acid in the form of Sauergut
2.3Cultivation and propagation of lactic acid bacteria
2.4Production of Sauergut in the brewery
2.5Calculating the required volume of lactic acid
3Summary
4Overview
5References
YEAST TECHNOLOGY AND FERMENTATION
1Introduction
2Yeast Management and Fermentation
2.1Yeast viability and vitality
2.1.1Yeast viability
2.1.2Yeast vitality
2.2Yeast cultivation and assimilation techniques
2.2.1General information regarding yeast assimilation
2.2.2Procedures for yeast assimilation
2.2.3Designing a yeast assimilation system
2.3Yeast pitching technology and SO2 formation
2.4Fermentation
2.5Proper handling of cropped yeast
2.6Maturation and lagering
3Summary
4Overview
5References
FILTERABILITY – ISSUES WITH TURBIDITY
1Introduction
2Attributes Influencing Beer Filterability
2.1The impact of malt quality on beer filterability
2.2The impact of brewhouse operations on filterability
2.3The impact of fermentation and storage on the filterability of beer
2.4Monitoring the filterability of wort and beer as part of a stepwise quality control program
2.5The influence of filtration on turbidity in beer
3Summary
4Overview
5References
BEER FOAM
1Introduction
2Aspects of Beer Foam
2.1The physics of foam
2.2Biochemical and technological aspects of beer foam
2.2.1Compounds in beer with a positive impact on foam
2.2.2Compounds in beer with a negative impact on foam
2.3Influence of brewing techniques on beer foam
2.4Methods for determining foam stability
3Summary
4Overview
5References
SENSORY ANALYSIS
1Introduction
2Sensory Analysis in the Brewing Industry
2.1Sensory evaluation of beer
2.1.1Discriminative tests
2.1.2Descriptive tests
2.1.3Evaluation tests
2.1.3.1Tasting scheme for determining aging according to Eichhorn
2.1.3.2Tasting scheme according to Kaltner
2.1.3.3EBC Descriptive Analysis
2.1.3.4Tasting scheme for wheat beers
2.1.3.5Modified “trueness-of-type” scheme
2.2Designing rooms for preparing and performing sensory analysis tests
2.3Selecting and training a tasting panel
2.3.1Selecting candidates to serve as members of the tasting panel
2.3.2Training to identify the basic tastes
2.3.3Training with reference substances
2.3.4Consumer taste tests – expert taste tests
2.3.4.1Consumers as tasters in sensory tests
2.3.4.2Experts as tasters in sensory tests
2.4Statistics in sensory analysis
2.4.1Univariate evaluation methods
2.4.2Multivariate evaluation methods
3Summary
4Overview
5References
FLAVOR STABILITY
1Introduction
2Aspects of Flavor Stability
2.1The fundamentals
2.1.1The aging process
2.1.2Reaction pathways of compounds relevant for aging
2.1.3Effects of antioxidants
2.2Influencing flavor stability in the brewing process
2.2.1Barley and malting
2.2.2Milling and mashing in
2.2.3Mashing
2.2.4Wort production and wort handling
2.2.5Fermentation
2.2.6Lagering and filtration
2.2.7Filling
2.3Analytical evaluation of flavor stability
2.3.1Sensory analysis
2.3.2Detection of aging indicators using gas chromatography
2.3.3Analytical evaluation of the antioxidative capacity
2.3.4Determining the reductive capacity
2.3.5Stability test
2.3.6Helpful tips for sample collection and storage for stability tests
2.3.7Thiobarbituric acid index (TBI) and aniline number (AN)
2.3.8Absorption integral (AI)
3Summary
4Overview
5References
SOUTHERN GERMAN WHEAT BEER
1Introduction
2Brewing Techniques in Wheat Beer Production
2.1The basics
2.2Wheat as a raw material and in the grain bill
2.3Mashing
2.4Wort boiling procedures
2.5Fermentation
2.6Maturation
2.7The aging process in wheat beer
2.8Unique aspects of wheat beer production
2.9Haze stability in wheat beer
3Summary
4Overview
5References
NON-ALCOHOLIC BEER
1Introduction
2Production Methods for Non-alcoholic Beers
2.1Physical removal of alcohol
2.1.1Thermal removal of alcohol
2.1.2Extraction with CO2
2.1.3Membrane separation method
2.1.3.1Reverse osmosis
2.1.3.2Dialysis
2.2Biological method
2.2.1Interrupted fermentation
2.2.2Bioreactors
2.3Combined technologies
2.4Economic aspects
3Summary
4Overview
5References
BEER RECOVERY
1Introduction
2Utilizing Beer Recovered from the Production Process
2.1The significance of beer loss
2.2Recovering beer from surplus yeast
2.2.1Expansion tank
2.2.2Yeast sieve or filter
2.2.3Yeast chiller
2.2.4Yeast storage tank (surplus yeast)
2.2.5Beer recovery systems
2.2.6Flash pasteurization
2.2.7Storage tanks for recovered beer
2.2.8Surplus yeast tank
2.2.9Qualitative aspects of recovered beer
2.2.10Economic aspects of beer recovery
2.3Beer losses during filtration
2.3.1Required equipment
2.3.1.1Pre-run and post-run collection tank
2.3.1.2Adding recovered beer during production
2.4Other recovered beer streams
2.5Avoiding beer loss and subsequent beer recovery
3Summary
4Overview
5References
BEER AND HEALTH
1Introduction
2The Effects of Beer on Human Health
2.1Nutritionally relevant substances in beer
2.1.1Polyphenols
2.1.2Vitamins
2.1.3Alcohol
2.1.4Carbon dioxide
2.1.5Water
2.1.6Minerals
2.1.7Maillard products
2.1.8Dietary fiber
2.1.9Bitter acids in hops and hop oils
2.2Beer – a valuable contribution to the human diet
2.3Enriching or excluding particular substances in beer
2.3.1Increasing xanthohumol content
2.3.2Increasing folic acid content
2.3.3Avoiding gluten
3Overview
4References
MICROBIOLOGY
1Introduction
2Microorganisms
2.1Pure brewing yeast strains
2.2Foreign yeast strains
2.3Beer-spoiling bacteria
2.4Detection of beer spoilers
2.4.1Detection of beer-spoiling bacteria
2.4.2Swab samples from biofilms
2.4.3Rapid methods based on molecular biology
2.5Detection and identification of yeast strains
3Summary
4Overview
5References
BREWING WITH MALTED AND UNMALTED CEREALS AND PSEUDOCEREALS
1Introduction
2Carbohydrate-rich Grains
2.1Cereals
2.1.1Barley (Hordeum vulgare L.)
2.1.2Oats (Avena sativa L.)
2.1.3Minor millets
2.1.3.1Pearl millet (Pennisetum glaucum [L.] R. Br.)
2.1.3.2Foxtail millet (Setaria italica [L.] P. Beauv.)
2.1.3.3Fonio (Digitaria exilis)
2.1.3.4Teff (Eragrostis tef[Zucc.] Trotter)
2.1.3.5Finger millet (Eleusine coracana [L.] Gaertn.)
2.1.3.6Proso millet (Panicum miliaceum L.)
2.1.4Maize or corn (Zea mays L.)
2.1.5Rice (Oryza sativa L.)
2.1.6Rye (Secale cereale L.)
2.1.7Sorghum (Sorghum bicolor L.)
2.1.8Wheat species (Triticum L.)
2.1.8.1Spelt (Triticum aestivum ssp. spelta Thell. = Triticum spelta L.)
2.1.8.2Einkorn (Triticum monococcum L.)
2.1.8.3Emmer (Triticum dicoccum Schübl.)
2.1.8.4Tetraploid free-threshing (naked) wheat (e.g. durum wheat Triticum durum L., rivet wheat T. turgidum L. and kamut, either T. t. ssp. polonicum [L.] Thell. or ssp. turanicum [Jakubz.] A. Löve and D. Löve)
2.1.8.5Triticale (× Triticosecale Wittmack)
2.1.8.6Tritordeum (hexaploid)
2.1.8.7Wheat (Triticum aestivum L.)
2.2Pseudocereals
2.2.1Amaranth grain (primarily: Amaranthus cruentus, A. hypochondriacus and A. caudatus)
2.2.2Buckwheat (Fagopyrum esculentum Moench)
2.2.3Quinoa (Chenopodium quinoa Willd.)
3Summary
4Overview
5References
SPECIALTY BEER
1German Brewing on the World Stage
2German Beer Styles
2.1Bottom-fermented Beers
2.2Top-fermented Beers
3International Specialty Beers
4International Beer styles
APPENDIX
1Compounds found in Wort
2Compounds Found in Beer
3Aroma Compounds and Higher Alcohols Found in Beer
4Indicator Compounds for Aging
5Conversion of Units
6List of Abbreviations
7Index
Malt quality is of great consequence in beer production and thus has a substantial impact on the quality of the finished beer. Individual production steps, e.g. lautering, fermentation and filtration, as well as attributes central to the character of beer, e.g. flavor, color, foam and stability, are heavily influenced by malt quality. The malt utilized in beer production is mainly produced from malting barley; however, for some specialty beers, e.g. Southern German-style wheat beer, malt is also produced from wheat or even other cereals, e.g. rye or oats (cf. Cereals and Pseudocereals). Barley is a natural product, making it subject to regional and seasonal fluctuations. The task of compensating for this variation, at least to the extent physically possible, falls to the maltster whose vocation it is to make homogeneous malt of a consistent quality available to breweries. However, biological and economic constraints limit the degree to which quality can be rectified in the malthouse. Maintaining high standards of quality for German malting barley and, in turn, for the malt created from the barley for the purpose of brewing beer, is the responsibility of the entire production chain, from the farmer to the brewer. Advancements in barley breeding and cultivation have resulted in malting barley of an extremely high quality, particularly spring barley varieties. Specifications define the quality of malt required for effortless processing and thus have become the standards used by malt producers and other processing companies.
Through selection of the barley variety and the level of malt quality and hence the standard values and thresholds for the quantifiable attributes described in the malt analysis, a brewer ultimately determines the quality of the raw materials required for a particular beer style. When deciding which attributes should receive the highest priority, the accuracy of the analyses as well as how these various attributes interact with one another should be taken into account. Meticulous attention must be exercised in obtaining analysis results. The procedures for conducting the brewing analyses established throughout Europe have been published in collections of brewing analysis methods by the Mitteleuropäische Brautechnische Analysenkommission (Central European Brewing Technology Commission or MEBAK) and by the European Brewery Convention (EBC) [1, 5].
The laboratory mashing method for the evaluation of malting barley varieties was changed prior to the 2012 harvest. The Congress mash method was replaced with an isothermal 65 °C mash (similar to hot water extract), allowing a more practically oriented assessment of new barley varieties to be carried out while also providing insights into processability [2]. However, when evaluating malt quality, the results obtained with the Congress mash method are not equivalent to those found with the isothermal 65 °C mash method. In this situation, comparative analysis is needed to find a common basis. Direct conversion factors will certainly never be generated for adapting the pool of data collected for the Congress mash method to the data for the isothermal 65 °C mash method [3]. Due to the considerably advanced proteolytic and cytolytic modification of grain accomplished in the malthouse, brewers can concentrate their efforts on degrading the starch in the mash vessel (cf. Mashing). Before discussing the individual attributes measured in malt analysis, one should understand that the quality of the assessment itself, as well as the quality of a particular lot of malt, largely depends on representative sampling. The importance of collections, along with the rules governing collection and the preparation of samples, have been described in numerous publications [1, 6, 4].
First and foremost, a barley malt analysis describes the three primary modification processes that have occurred in the kernel: cytolysis, proteolysis and amylolysis. The single most important task of the maltster, given the fact that modern brewhouse procedures often entail mashing in at temperatures above 60 °C, is to effect a homogenous and complete degradation of the cell walls and to attain a suitable level of protein modification. Thus, malt quality plays a key role in ensuring that the production process runs smoothly. In large breweries, where up to twelve batches of wort are brewed per day, modifying the temperatures and rests in the mash program to accommodate individual fluctuations in malt quality is not practicable if brewing operations are to remain on schedule. Thus, mashing is largely limited to amylolysis, that is, the degradation of amylose and amylopectin required for brewing (cf. Mashing).
Cytolysis describes the degradation of the substances providing structure and support to the cells that surround the starch in the endosperm. Structural proteins and polysaccharides in the cell wall, especially β-glucans, are subject to these degradation processes. If the processes are allowed to continue during malting until the support structures of the cells are largely broken down, the enzymatic degradation of the endosperm during mashing is much less arduous, resulting in higher brewhouse yields. Likewise, insufficient modification of these support structures not only brings about shortfalls in brewhouse yield but also causes large quantities of high molecular weight β-glucans to become soluble and enter the process of wort production.
Older sources attest to the favorable influence of high molecular weight β-glucans on foam and mouthfeel. As long as the β-glucans are not in gel form, quantities of up to approximately 350 mg/l do not pose a problem from a brewing standpoint (isothermal 65 °C mashing procedure)[7, 8, 9]. β-Glucan gel can lead to filtration issues even at concentrations as minute as 10–15 mg/l, a level only slightly above the reliable detection threshold (cf. Filterability – Issues with Turbidity). Wort produced using mash programs with mash-in temperatures above 60 °C are particularly susceptible to gel formation. At mash temperatures in the range from 60 to 65 °C, a substantial amount of β-glucans still bound to the cell walls is liberated by the enzyme β-glucan solubilase. However, degradation of this high molecular weight fraction can no longer take place, since the endo-β-glucanases – the enzymes responsible for breaking down these large β-glucans – are inactivated at temperatures as low as 52 °C. Thus, given a consistent malt quality, brewhouse procedures incorporating high mash-in temperatures will always lead to higher total β-glucan concentrations in wort and beer. For this reason, high mash-in temperatures require more extensive modification of the cell wall (cf. Mashing).
Various key metrics are used to describe the level of cytolytic modification. The value for friability has proven useful in this regard. The procedure is simple, and the value can also be ascertained rapidly. Cell wall modification is evaluated with a friabilimeter to determine the overall friability of a specific lot of malted grain and the percentage of kernels that are classified as completely glassy. This information is then used to draw a conclusion regarding how uniform the process of malting the barley has been. High values for friability are not necessarily an indication of over-modification, as long as they only apply to cell wall modification and not to protein modification. Therefore, breeders involved in developing malting barley varieties face the challenge of striking the right balance among the individual traits used to define modification, especially with respect to proteolytic and cytolytic processes.
Other attributes providing information about the degree of cytolytic modification include the viscosity and the β-glucan content of both the Congress wort and of the 65 °C mash as well as the homogeneity and modification of the malt. The values obtained for the 65 °C mash are a better gauge of cytolytic modification than the values obtained with the Congress mash.
Owing to the 45 °C rest, the Congress mash method promotes more β-glucan degradation. However, with this method, once the temperature of the mash reaches 45 °C, it is immediately heated to 70 °C, which does not allow enough time for an adequate β-glucan solubilase rest. Thus, variation in cytolytic modification among different lots of malt cannot be sufficiently characterized by means of the Congress mash method. The isothermal 65 °C mash, on the other hand, more clearly distinguishes this variation with its high mash-in temperature and intensive β-glucan solubilase rest. From time to time, the difference in the results between the Congress mash and the isothermal 65 °C mash is also employed as an assessment criterion. One should be mindful of the fact that both MEBAK and the EBC no longer include the method for determining the difference in extract between fine and coarse grist in their analysis collections. Based on statistical evaluation in combination with practical tests, the following analysis results and limit values have been shown to be useful for mash programs utilizing high mash-in temperatures.
friability |
> 85 % |
whole glassy kernels |
< 2 % |
viscosity, isothermal 65 °C mash (adj. to 8.6 %) |
< 1.6 mPa·s |
β-glucans, isothermal 65 °C mash (adj. to 8.6 %) |
< 350 mg/l |
homogeneity |
> 75 % |
Table 1:Cytolytic malt analysis attributes for mash programs utilizing high mash-in temperatures (isothermal 65 °C mashing procedure)
Practical experience has shown that it is prudent to determine the viscosity of the isothermal 65 °C mash in addition to the friability (including the glassy kernels) and homogeneity as part of a routine analysis program. Only in cases of considerable uncertainty (results exceed or fall below the limit values) would it be worthwhile to perform the remaining analyses in table 1. Interpretation of the results is recommended as follows: If the results for at least two of the analyses fall outside of the range for the limit values given, then mashing in at a high temperature with the malt in question can lead to difficulties during lautering and filtration. If, on the other hand, the results remain within the limit values and filtration issues arise, these can most likely be traced back to errors in brewing techniques (cf. Filterability – Turbidity Problems). If only one of the values exceeds the limit, then the analysis should be repeated. In some instances, the analyses to determine the percentage of whole glassy kernels and the concentration of β-glucans exhibit very poor reproducibility. The corresponding statistical data analysis can be found in the collection of analysis methods published by MEBAK or EBC. Low values for homogeneity and a disproportionate rise in the viscosity and the concentration of β-glucans in the Congress wort compared to the values from the 65 °C mash indicate that highly modified malt has been mixed with slightly modified malt [10].
Proteolysis describes the degradation of the protein in the kernel and its resultant transformation into more soluble molecules, which can be of a low, medium or high molecular weight. While extensive cell wall modification does not impact beer quality in either a positive or negative manner, it does improve processability. Both excessive and negligible levels of protein modification are regarded as detrimental. Low protein modification carries the risk of depriving the yeast of assimilable nitrogen compounds. Negative outcomes include inadequate yeast reproduction and the formation of undesirable fermentation by-products (e.g. diacetyl). On the other hand, a high level of protein modification results in excessive degradation of high molecular weight proteins. A dearth of sufficient concentrations of high molecular weight proteins – but also a surplus of medium molecular weight proteins and certain amino acids (lysine, arginine and histidine) – has a negative effect on foam stability. Malt subjected to elevated levels of protein modification produces wort and beer that tends to be darker in color and contains an overabundance of certain amino acids. The presence of these amino acids leads to the production of uncharacteristic aromas in beer, along with reduced flavor stability (cf. Flavor Stability). Furthermore, beer containing higher concentrations of amino acids is more susceptible to beer spoilage microbes.
The Kolbach index (degree of protein modification), the soluble nitrogen content and free amino nitrogen (FAN) are key metrics for proteolysis. The Kolbach index is the most commonly used metric for assessing proteolysis in commercial breweries. It represents the percentage of the total protein converted into soluble form during malting and subsequently during the Congress mash (calculated value). The preferred range for pale, all-malt beers is between 38 and 42 % (Congress mash method). The degree of protein solubility limits the possibilities for theoretical combinations derived from the absolute values for the protein content of the malt (standard values: 9.5–11 %) and the soluble protein (standard values: 3.9–4.7 %). This is intended to ensure that the overall composition of soluble protein is balanced in the ranges of both the high molecular weight (foam stability) and the low molecular weight (yeast nutrition) proteins, independent of the total protein content of the malt. Soluble protein is calculated by determining the soluble nitrogen (conversion factor: 6.25) in most cases. Consequently, calculations based on the data above yield values of 650 to 750 mg of soluble nitrogen per 100 g of malt (dry matter) and 130 to 160 mg of FAN per 100 g malt (dry matter) which should account for approximately 21 % of the soluble nitrogen (Congress mash method). A curtailed mash program or the use of adjuncts, such as rice or corn, would mean that higher amounts are required (cf. Cereals and Pseudocereals).
Of the metrics available for amylolytic activity, the following measurements are routinely performed: extract, limit of attenuation, β-amylase activity (expressed as diastatic power in WK units or β-amylase activity in BU) and α-amylase activity (ASBC or DU, using a Megazyme kit). The extract content indicates the percentage of finely milled malt (dry matter) that can be solubilized using the laboratory mash method and gives an indication of the expected yield during the brewing process. In the case of barley malt, the values are between 78.0 and 83.5 % (Congress mash method).
The limit of attenuation is a metric for evaluating the quality of wort in a laboratory and provides information on how well the extract can be metabolized by the yeast. The degree of final attenuation reached in the finished beer at a brewery should be compared to the laboratory results for the limit of attenuation. The final attenuation should be equal to or as close as possible to the limit of attenuation. The quantity of fermentable sugars and their relative proportion are the defining factors for the limit of attenuation; however, it is also affected by the gelatinization temperature of the starch (cf. Mashing). In addition, the role of trace elements and the nitrogen composition should also not be underestimated. As a measure of quality of the Congress wort, the following applies: the higher the limit of attenuation, the better (> 81 %). Final attenuation in the brewery is sometimes disproportionately high and can be difficult to control. Within this context, there is some discussion as to whether or not attempts should be made to regulate the limit of attenuation in the malt (cf. Acidification with Natural Lactic Acid). The β-amylase activity of malt is primarily of interest outside of Germany, e.g. in countries where large quantities of adjuncts are used. These adjuncts usually contribute very little enzymatic activity of their own. For an all-malt beer, values for β-amylase activity greater than 200 WK or 750 BU, respectively, are considered adequate. If β-amylase activity is too low, this can cause a shift in the sugar spectrum and may result in abnormal fermentations in extreme cases (diauxie).
The pace-setting enzyme during starch degradation is α-amylase. It degrades starch into fragments consisting of amylopectin and amylose, providing substrate for β-amylase. An α-amylase activity of more than 60 ASBC units or DU is desirable. If the mash is acidified, α-amylase activity may be inhibited to some extent (pH optimum: 5.4–5.6). If the gelatinization temperature of a given lot of malt is high, it would be beneficial to avoid acidification during mashing, since this could result in increased iodine values. Furthermore, undesirable consequences may arise as well, such as higher values for turbidity in the filtered beer. Furthermore, a lack of available substrate for β-amylase can adversely impact the limit of attenuation (cf. Mashing).
The DMS precursor (DMS-P), otherwise known as S-methylmethionine (SMM), is an amino acid not found in barley in its unbound form, but it is present in malt.
Dimethyl sulfide (DMS) splits off of the larger DMS-P molecule at above approximately 70° C, essentially at every stage of malt and wort production in which thermal processes exceed that temperature.
The vast majority of DMS should be cleaved from the DMS-P molecules and eliminated during malt kilning and wort boiling. One should be cognizant of the fact that DMS will continue to be formed in the whirlpool (cf. Wort Boiling, Wort Boiling Systems). The temperature and duration of curing during kilning are the most effective means for influencing the level of DMS-P in the malt. In principle, the following applies: the higher the temperature or the longer the duration of curing, the lower the level of DMS-P in the malt. However, economic considerations and excessive thermal stress (see TBI) can be detrimental to pale malt and thus serve as arguments against curing longer at higher temperatures.
DMS can create flavor and aroma impressions in the finished beer that are reminiscent of boiled cabbage or cooked vegetables. The sensory threshold for free DMS in beer is approximately 50–100 μg/l. Therefore, depending on the intensity of the wort boiling process, the DMS-P content of malt should not exceed 5–7 ppm (cf. Wort Boiling, Wort Boiling Systems).
The TBI is a metric representing the sum of the thermal stress to which the malt has been subjected during the kilning process. Maillard products deepen the color of the malt and the finished beer and may, in part, have a negative impact on the beer’s flavor stability. These compounds are formed in reactions brought about by thermal stress. For pale malt, the TBI measured in the Congress wort should not exceed 18, and the values for DMS-P must be reduced to below the recognized upper limit. As already stated above and is often the case in malting and brewing technology, a compromise must be reached between the lowest possible thermal stress on the malt and the cleavage of DMS-P along with the elimination of DMS when determining the intensity of the kilning process (fig. 1).
Figure 1:Relationship between the temperature/duration of kilning and the TBI/DMS-P content in malt according to FORSTER [8].
For example: a concentration of 5 ppm DMS-P is obtained under the following conditions 3.2 h/84 °C/TBI=14.5 or 5.5 h/82 °C/TBI=18.
Obviously, the color of the malt significantly influences the color of the finished beer. Both are determined photometrically or visually from Congress wort samples (unboiled or boiled). In comparing analytical results, one should note which methods were used to determine the color. Pale malts used to produce Central European lager beers should possess a color between 2.5 and 3.5 EBC. The color itself is indicative of the malt and how it was produced. In principle, the color of the boiled wort can be used to predict the color of the finished beer if information is known about the brewing techniques employed. The thermal stress brought about by the brewing process, any potential oxidation processes (especially during mashing) and the extent of the pH drop during fermentation all have a considerable influence on the beer color, independent of the malt color. The application of less intense wort boiling methods and low thermal stress on both the malt and the wort can result in finished beer that is too light in color. In such cases, the desired color can be adjusted by adding of any number of specialty malt products [10, 12].
The pH of the malt is determined by measuring the pH of the Congress wort. For pale barley malt, the pH should range from 5.80 to 5.95. Darker malts possess a larger quantity of Maillard products and thus a lower pH, which varies between 5.50 and 5.80. If the pH of pale malt is too low, this can be an indication that it has been overly modified or too intensely sulfured. One can expect that the mash produced using malt of a low pH will also exhibit a low pH.
The criteria for assessing the quality of wheat malt were appropriated directly from those for judging barley malt. Since the technological requirements are different for the production of Southern German wheat beers, a critical view of these quality criteria is therefore necessary. The differences in barley and wheat as well as in clear, bottom-fermented beer and cloudy, top-fermented beer require a fundamentally different approach to the raw materials. The quality of wheat, the capacity to convert wheat to malt and the influence of the malt quality on that of the wheat beer, are not nearly as well researched as the same characteristics in barley and barley malt. Nevertheless, in each respective section of the discussion below, the properties of wheat malt are compared to the properties of barley malt and, where relevant, their similarities and differences are also examined [4].
The polysaccharide β-glucan, which is present in the cell walls of barley malt, is the primary focus of the analyses for characterizing the cytolytic processes involved in malt modification, and it also largely determines the viscosity of wort produced from barley malt. Staining β-glucans with calcofluor provides the analytical foundation for evaluating the homogeneity of malt or for directly determining the concentration of β-glucans in wort and beer. Wort brewed with wheat malt generally exhibits a higher viscosity (1.6–1.8 mPa·s in Congress wort) than wort brewed with barley malt. However, the viscosity is not attributable to β-glucans, but rather to other polysaccharides called pentosans. Little is known concerning their behavior during the processes of malting and brewing. It has been reported that if they are exposed to hot side aeration during mashing, the pentosans in rye malt can increase the viscosity of the wort quite dramatically, leading to difficulties in the lautering process [13]. Nevertheless, although gel formation has been documented with β-glucans, its formation in beer containing pentosans has yet to be demonstrated. With regard to the aforementioned analysis of barley malt and the evaluation of its cytolytic modification, one should keep in mind that not all of the tests based on β-glucans are applicable to wheat malt. In essence, the analyses used to assess the homogeneity of barley malt as well as the direct determination of β-glucans in wort and beer are not relevant for judging the quality of wheat malt. Moreover, the friabilimeter test is of little value in determining how friable the structure of the endosperm is in wheat malt. For this reason, only the viscosity remains as a means for assessing the level of cytolytic modification. Unfortunately, the results for the viscosity of Congress wort produced with wheat malt cannot be adequately correlated with lautering behavior or filterability in the production of Kristallweizen (filtered Southern German wheat beer) (cf. Filterability – Issues with Turbidity). However, given the fact that no other parameters exist for evaluating the processability of wheat malt, viscosity is currently the only reliable indicator for the degree of cytolytic modification in wheat malt.
The analyses used to assess the proteolytic modification of barley malt are also used for wheat malt: total protein (conversion factor: 6.25), soluble protein, the Kolbach index (the quotient derived from these two values) and FAN. Protein modification in wheat malt has a significant impact on the aroma of weissbier [14]. Research results indicate that more extensive proteolytic modification results in the formation of fewer esters, thus leading to more neutral beers.