Application of Advanced Instrumental Techniques for Analysis of Physical and Physicochemical Properties of Beer: A Review

Abstract

Beer, a brewed beverage made principally from malt (germinated barely), hop, water, and yeast, is among the most popular drinks worldwide. Qualitative aspects of beer play a crucial role in its acceptability among the consumers. Part of this can be related to physical and physicochemical properties of beer. Foam, colloidal stability, color and transparency, and body of beer are classified under this category. In this review, the application of advanced instrumental techniques to measure all those properties is discussed.

Keywords:

• Analysis
• Beer
• Body
• Colloidal stability
• Color
• Foam

INTRODUCTION

Beer is a worldwide consumed and universally popular beverage. This is due to its satisfactory sensory properties, nutritional/medicinal functions and also due to its reasonable cost. In 2004, the per capita consumption of beer around the world was 72.9 L on average, while in some countries this figure was higher than 130 L.[1] Evidences indicate that beer has also been a popular drink in many ancient cultures. According to established documents, numerous types of beer and beer-like beverages from different grains were industrially manufactured in some ancient countries such as Egypt, Rome, China, India, and Iran.[2]

Most beers produced worldwide have alcohol content in the range of 3–6% (v/v).[3,5] Popularity and brilliant image of beer in consumers' mind relies on its qualitative aspects, which are so-called “functional qualitative aspects” when considering consumers points of view.[6] These qualitative aspects can be divided into four categories: physical and physicochemical, chemical and biochemical, microbiological, and sensory evaluation.[6]

To maintain a consistent product quality, these quality attributes have to be measured along the production line and, as a consequence, advanced instrumental techniques for the quick and reliable analysis of the products are highly demanded for quality evaluation purposes. Therefore, the objective of this study was to investigate on the recent applications of the analytical instruments for measuring the physical and physicochemical properties of beer.

PHYSICAL AND PHYSICOCHEMICAL ANALYSIS

Analytical methods related to the physical characteristics of beer can be considered in two ways: foreground analysis and background analysis. In the former, the devices/instruments are intended to assess some representative parameters from a phenomenon. However, in the latter, the instruments determine the type and amount of responsible chemical compound(s), and the results are correlated with the measured representative parameters. As an example, foam stability of beer can be easily assessed by generating foam with gas bubble and measuring the collapse time. On the other hand, the amount of well-known foam producing agents in beer can be determined by chemical analytical methods. Therefore, to have complete information, both procedures are required. In the following sections, different methods dealing with foam; colloidal stability; color, transparency (clarity and turbidity) and visual impressions, and also those dealing with textural sensation of body (including rheological properties) of beer are discussed.

Barley, malt, water, hops, and yeast are major ingredients for making beer. The process for brewing normal beer consists essentially of the following steps:

• malting (steeping, germinating, kilning) barley,

• crushing the malted barley to create the “grist,”

• adding water to the grist to create the mash (infusion and decoction mashing), separating the resultant aqueous extract known as “wort,”

• boiling the wort with hops,

• cooling and clarifying the wort,

• fermenting the wort with the brewer's yeast (primary fermentation) to produce the “green” or “young” beer,

• maturing or “lagering” the fermented young beer by means of “secondary fermentation” using the same yeast,

• filtering,

• adding other additives,

• pasteurizing, and finally,

• packaging the beer.

Malted barley can be partially replaced by adjunct grains (such as maize and rice). Sugar, various syrups, starch-containing mixture and different types of additives might also be added to the beer.[3,4] Beer characteristics can be influenced by the variety of barely used for the brewing and the conditions applied in each of the above steps.[3,4]

Foam

Foaming in beer is a mixed property that includes the CO₂ retention power and level of foam stabilization. Therefore, some parameters such as foam-head formation on top of the glass (foam head retention), foam quantity, lacing (adhesion or cling), bubble hazing, and bubble gushing (bursting or effervescence)[6,7] are involved in foaming. Appropriate foam-head stability in beer in a glass is deemed as a desirable characteristic for it. Polypeptides (especially proteins with MW > 5000 and higher hydrophobic area), peptides, glycoproteins, phenolics (such as hops iso-alpha-acids and their oxidized or reduced derivatives as well as isohumulone and isoadhumulone), dextrines, high molecular weight non-starch polysaccharides such as β-glucans and arabionoxylans and some types of gums, which naturally occur in beer, glycerol and/or sugar alcohols, iron, manganese and aluminum, melanoidins, ethanol and also a low pH are all positively correlated with foam properties of beer.[7–12] Conversely, straight chain higher alcohols and their acetate esters as well as the lipids adversely affect the foaming properties of beer.[7,11]

The most common methods of foam assessment are based on artificial formation of foam in beer and measuring its collapse time or drainage rate. These methods differ only in how the foam is formed and how the drainage is assessed. For example, the “Rudin” method foams up a sample of degassed beer by passing CO₂ through a sintered disk.[13] The Institute of Brewing in the US approved the measurement of foam stability according to “Rudin” method using “NIBEM meter.”[14] The new models of NIBEM foam stability meter (NIBEM-T meter) have the advantages of air movement and automatic temperature compensation as well as better repeatability and reproducibility.[15] Foam collapse time (duration of foam head retention) correlates well with the consumers observations of foam.[16,17] The American Society of Brewing Chemists (ASBC) describes a foam flashing method (FFM) for bottled beers.[7] Recently, photographic methods (optical techniques) have been used to estimate parameters such as bubble size and bubble distribution in foam as well as lacing or cling (foam adhesion) on beer glasses.[14,17,18] Measurement of bubble volume by ultrasound is another bubble measurement technique.[18] Hepworth et al.[19] served a novel application of computer vision to determine bubble size distribution and bubble haze potential in beer. The technique is also designed to be simple to use and relatively portable. Based on this technique, a computer controlled camera is used to capture and save bubble images.

Scanning electron microscopy (SEM) is another method used for the microstructural analysis of foam stability, foam distribution and diffusion, bubble size, foam film thickness and dynamic foam collapse in foodstuff. However, similar studies with beer (as an aqueous-based product) were not found in the literature. Evans and Sheehan[20] showed that the measurement of beer proteins by the “Bradford Coomassie Blue Dye Binding Assay” (a colorimetric method measuring proteins with MW > 5000 only) correlated well with Rudin head retention values. Fractionation of beer protein by hydrophobic interaction chromatography[21]might be a good alternative for estimating foam potential of beer. The same determination can be done using dialysis with visking tubing or electrophoresis.[7] There have been some efforts to determine the protein profile of beer using simple assessment of ultraviolet absorbance by beer wort. However, other ultraviolet-absorbing materials such as bitter acids of hop interfere with the above absorbance.[17] Enzyme-linked immunosorbant assay (ELISA), which has been used for measuring the level of some protein fractions in malt,[22] could be an alternative approach to determine the protein profiles of beer. Size exclusion chromatography (gel filtration) is applied for the analysis of polypeptides in beer.[23] Bamforth et al.[24] explored a method for assessing hydrophobic polypeptides in beer by measuring fluorescence based on interaction of the proteins with 1-anilino-8-naphthalenesulfonate. No reliable method has so far been proposed for the assessment of gushing. However, gushing potential might be evaluated by analyzing some chemical indicators such as deoxyinvalenol (DON) (a vomitoxin produced by Fusarium spp.) using high performance liquid chromatography (HPLC) technique.[17] Selected publications pertaining to foam analysis of beer are shown in Table 1.

Table 1 Selected publications regarding foam analysis of beer

Parameter	Method of analysis	Source
Foam-head retention	Foam formation bear and measuring the collapse time, e.g., using “NIBEM-T meter” or foam falling method (FFM) for bottle beer	[7,13–15]
Bubble size and bubble distribution in foam as well as lacing & cling	Photographic methods/Optical techniques	[14,17]
Bubble volume	Ultrasound	[18]
Beer foaming proteins with MW > 5000	“Bradford Coomassie blue dye binding assay” (colorimetric method)	[20]
Fractionation of beer foaming proteins (including hydrophobic proteins)	Hydrophobic interaction chromatography	[21]
	Dialysis	[7]
	Electrophoresis	[7]
	Ultraviolet absorbance	[17]
	Enzyme-linked immunosorbant assay (ELISA)	[65]
	Size exclusion chromatography (gel filtration)	[23]
	Measuring fluorescence	[24]
Gushing potential	Assessing DON by HPLC	[17]
Bubble size distribution & bubble haze potential	Computer vision	[19]

Colloidal Stability

Colloidal stability of beer is recognized from its appearance. A simple observation of no precipitated materials (such as dregs), immersion (such as haze) or phase separation as well as a continued clarity and transparency in the beer are good indication of the stability in the colloidal state. In other words, colloidal shelf life refers to the length of time during which beer remains clear. Loss of colloidal stability in beer during the storage might adversely influence transparency, eye-appeal, smoothness and integrity, body, viscosity, and mouthfeel.[6] This phenomenon is attributed mostly to the condensation of polypeptides and polyphenols through cold storage of beer.[7] However, some of the metals such as copper, iron and aluminum, calcium oxalate, carbohydrates such as retrograded starch, β-glucans, and pentosans, as well as invading microorganisms such as bacteria or wild yeasts have been found to be also involved in beer haze.[7]

As an instrumental technique, haze meter (radiometer) works on the light scattering basis and has been used for the analysis of turbidity/haze characteristics in beer. Particles with diameters greater than 0.50 μm can be measured using this method.[16,25] Morris[25] investigated the relationship between haze and particle size using light scattering method. Formation of complexes between polyphenols and proteins during haze production leads to significant increase in particle size diameter in a colloidal system.[25] It should be pointed out that in most cases, visual assessment of beer haze correlates well with instrument reading from a light scattered at 90°; but some beers that appear bright to the eye give substantial meter readings due to the presence of invisible-/pseudo-haze characteristic.[7] Light scattering and obscuration, and laser Doppler anemometry methods that are used for haze analysis in beer both relate the level of scattered light to bubbles diameter.[19] Spectrophotometric techniques can also be applicable for relative assessment of haze since turbidity (cloudiness) caused by haze affects the proportion of light transmittance/light absorption.[7] Schultz et al.[26] and Etokakpan[27] have described a rapid ageing test for lagers based on measurement of beer haze-life using catechin and gliadin solutions.

Various electrodes (especially those related to conductometry) are available for the analysis of different ions associated with colloidal stability of beer. These ions can also be determined by using atomic absorption spectrometry (AAS) or ion chromatography techniques.[7] Based on ion-exchange separation and size exclusion chromatography, copper, iron and magnesium in beer were determined using electrothermal AAS.[28] However, due to relatively expensive instrumentation, the need for a highly skilled operator and complicated temperature programming the electrothermal AAS is not highly practical.[8,28] Instead, flame AAS was easily applied for the analysis of iron, magnesium, zinc, copper, manganese, cadmium and aluminum in beer. Sodium and potassium were determined by flame atomic emission spectrometry.[29] Due to high sensitivity and selectivity, good accuracy, adequate precision, large element coverage, moderately priced equipment and a well-established methodology, flame atomic spectrometry has been regarded as one of the most useful techniques for the analysis of trace metals. Iron and some other elements such as silver, cadmium, copper, indium, manganese, lead, titanium, and zinc were determined using an integrated-atom-trap system mounted on a standard atomic absorption air-acetylene flame burner.[30,31] Ampan et al.[8] detected trace iron in beer using flow injection (FI) system with in-valve column and bed injection[8] possibilities. Flow-based analysis with bead injection (BI) along with many detection systems such as amperometry,[32] fluorescence[33,34] and UV-Visible spectrophotometry[35] has been reported. Chloride can be measured by ion chromatography or conductometry.[7] Coelectroosmotic capillary electrophoresis has been successfully applied for the analysis of anionic species such as inorganic anions.[33,36,37]

Sikorska et al.[38] used synchronous scanning florescence techniques (fluorescence spectroscopy) for monitoring stability changes occurring in beer during storage under different conditions. The principal component analysis of synchronous scanning fluorescence spectra revealed clear clustering of samples depending on the storage conditions. Several studies in which colloidal stability analysis of beer have been applied are listed in Table 2.

Table 2 Selected publications regarding colloidal stability analysis of beer

Parameter	Method of analysis	Source
Turbidity and haze characteristics	Haze meter/ radiometer (based on light scattering method)	[16,25]
Haze analysis	Light scattering & obscuration	[19]
	Laser Doppler anemometry
	Spectrophotometric methodology
Analysis of ions (associated with haze)	Electrodes (conductometry)	[7]
	Atomic absorption spectroscopy	[7, 28]
	Ion chromatography	[7, 28]
	Flame atomic spectrometry	[29]
	Integrated-atom-trap system mounted on a standard atomic absorption air-acetylene flame burner	[31]
	Flow injection (FI) system with in-valve column & bed injection	[36, 37]
Inorganic anions	Coelectoosmotic capillary electrophoresis	[33, 37]
Monitoring changes in beer stability during storage period	Synchronous scanning fluorescence technique (Fluorescence Spectroscopy)	[38]

COLOR AND TRANSPARENCY

Beer might comprise a wide spectrum of colors such as dark, dark amber, brownish, red undertones and pale amber.[11,39] Considering the transparency, the “brilliant” appearance is mostly demanded by beer consumers. High turbidity is regarded as an inappropriate characteristic for beer. Various compounds present in beer such as sugars, amino acids, small peptides, simple- and polyphenols as well as some carbonyl compounds contribute in beer color. Melanoidins (polymeric and colored final products of Maillard reaction), which are among the most important colorants of beer, are responsible for its wide color spectrum from relatively dark yellow to dark brown. In some countries, caramel colorants are also added for darkening of beer.[7,11,39] Some compounds such as polyphenols contribute to beer color.[7] Purines, perimidines, nucleotides and polynucleotides formed during the malting process also impact beer color via interactions with other components.[11] Riboflavin can also contribute to beer color in pale beers.[7]

To measure color and clarity of beer, spectrophotometric measurement at a give wavelength has been a useful technique.[16,40] However, single-wavelength measurements can provide only limited information. Human eye cone cells respond to either red (600 nm), green (550 nm), or blue (450 nm) light and therefore send only these three signals to the brain, where they are integrated and perceived as the true color of the materials. In other words, color has these three components.[17,41] These components are commonly measured using a Hunter colorimeter based on three-color co-ordinates; namely “L,” “a,” and “b”. “L” represents brightness/lightness; “a” indicates the greenness or redness; and “b” represents the yellowness or blueness of the subject (beer in this case).[42] Color can be expressed as a single numerical ΔE value defining the difference in color levels. The ΔE value is expressed by the equation of ΔE = (ΔL² + Δa² + Δb²).[43] Spectrophotometry, as well as basic comparative methods (beer color viewed by eyes is compared against some standard color sources, e.g., in Lovibond method), work quite well within a narrow band of products and color, but both methods have poor reproducibility when a broader range of products is considered.[17]

Since melanoidins are the most important colorants present in beer, monitoring the changes in the amino acid content in beer can indicate the changes in the content of melanoidins. Gorinstein et al.[44] studied the changes in the protein and amino acid contents of beer using combined fluorometry, ion-exchange chromatography, gel-electrophoretic separation and Fourier transform infrared (FT-IR). Khatib et al.[45] determined (both qualitatively and quantitatively) the amino acids of a beer sample using two-dimensional J-resolved nuclear magnetic resonance (NMR) spectroscopy. NMR has been recognized as a comprehensive method for differentiation among different types of beers. By using NMR spectroscopy, different compounds such as nucleic acid derivatives, amino acids, organic acids, alcohols, carbohydrates, and vitamins can directly be measured by relative intensities of their signals eliminating the need for a calibration curve for each compound. One advantage of using NMR is the reproducibility of the measured spectra. However, the complexity of NMR spectroscopy (i.e., the interpretation of the data) is a drawback for its use in the analysis of beer.[45] HPLC has been reported as a suitable method for the determination of amino acids in beers.[46] Electrophoresis has been reported for the determination of both amino acids and peptides.[47] Kutlan and Molnar.[48] proposed a new HPLC method for the simultaneous quantization of amino acids and amines by o-phthaldialdehyde (OPA) derivatization of these compounds. Thorsten and[49] quantified enantiomeric amino acids (L-amino acids and D-amino acids) by using GC complemented by an HPLC analysis. Table 3 lists several published articles on the analysis of beer color and transparency.

Table 3 Selected publications regarding colour and transparency analysis of beer

Parameter	Method of analysis	Source
Colour and clarity analysis	Spectrophotometric measurements at a fixed wavelength (430 nm)	[16]
	Commercial tristimulus	[41]
	Transmission instruments	[17, 41]
Monitoring changes of amino acid content (representative of “melanoidins” formation)	Combined fluorometry, ion-exchange chromatography, gel-electrophoretic separation & Fourier transform-infrared (FI-IR) spectra techniques	[44]
Determination of amino acid content (representative of “melanoidins” formation)	Two-dimensional J-resolved nuclear magnetic resonance (NMR) spectroscopy	[45]
	HPLC	[46]
	Electrophoresis	[47]
	HPLC by o-phthaldialdehyde (OPA) derivatization of amino acids	[48]
L-and D-amino acids content	GC complemented by HPLC	[49]

BODY

The body of beer is characterized during the dispensing, circulating and drinking. A “light” body for beer is defined as favorable body from the consumers' point of view.[6] Different substances including seed gums (such as β-glucans and arabinoxylans), dextrins, polyphenols, fatty acids, some additives such as silica gel, polyvinyl-polypyrolidine (PVPP) and glycerol as well as polynucleotides are known as viscosity enhancers and body improvers.[7,10,11] Excessive amounts of β-glucans cause soupiness texture and degrade smooth mouthfeel, while deteriorating sharpness and live sensations. Polyphenolic compounds at high concentration levels might also increase roughness in the mouthfeel of beer.[11] Carbon dioxide influences mouthfeel via formation of wriggling sensation in mouth and stomach.[6] pH values less than 4.0 improve mouthfeel of stored beer.[50] Lactic acid bacteria, acetic acid bacteria as well as wild yeasts might deteriorate the body of beer due to the formation of ropiness.[11,51,52]

Two types of viscosities can be measured for beer. One is a shear-free viscosity, where no velocity gradient is present among constituent liquid layers when the liquid flows downward. The other type of viscosity is shear viscosity, which is assessed using a rheometer.[53] The shear-free viscosity can be assessed by allowing the liquid to flow through an orifice under (the gravity force at 20°C) and measuring the flow time. Oswald viscometer is an international device for this purpose.[7] Assessment of this type of viscosity, therefore, does not require the use of advanced instruments.

Rheometer is capable of assessing viscous properties of liquids including beer (Newtonian or apparent viscosity) as well as viscoelastic attributes of pastes, semi-solids and solids (dynamic assessment indexes). In non-Newtonian fluids, the shear viscosity is reported by the word ‘apparent viscosity or η’. Apparent viscosity is measured as a function of shear rate or as a function of time at a fixed shear rate. Although beer is a colloidal system, its viscosity has been reported as Newtonian, due to low concentration of colloidal materials in aqueous phase.[11] Not many reports were found on the rheological properties of different types of beers. There is also lack of information correlating the compatibility of the sensory evaluation data with the instrumental viscometric behaviors.

Surface tension of beer can be analyzed by using a tensiometer. Surface tension is usually proportional to rotational viscosity.[54,55] Light scattering techniques can provide useful information for the interpretation of beer rheological behavior since the mean diameter of dispersed particles in an aqueous system can impact its viscosity.[56]

Quantitative determination of chemical substances influencing the viscosity is another approach for the prediction of beer viscometric behaviors. Dextrines have been analyzed using gel chromatography.[57] The contents of non-starch polysaccharides (such as arabinoxylans and β-glucans), which contribute to beer viscosity, have been reportedly determined by using GC and GC-MS after a methylation stage. [58–64] Amount of polyphenols were quantitatively determined by a non-specific spectrophotometric method based on the color formed with ferric ammonium citrate (measured at 600 nm). Catechin can be used as standard.[7] The polyphenols quercetin, rutin, catechin and epicatechin have been quantified in beer using HPLC.[65,66] Whittle et al.[67] examined the polyphenols (20 procyanidin dimers and trimers) by applying an HPLC system equipped with an electrochemical detector. Light absorption of an iso-octane extract of acidified beer at 275 nm can be used as a routine method for the determination of principal bettering agents in beer (isocohumulone, isohumulone, and isoadhumulone).[7 Both GC and GC-MS have been used to study the content of isoflavonoids in beer.[68] Lapcik et al.[68] developed radioimmunoassays specific for daidzein and its 4′-derivatives (formononetin, 4′-sulfate and 4′-glucuronide of daidzein) and for genistein and its 4′-derivatives (biochanin A, 4′-sulfate and 4′-glucuronide of genistein). They reported these components as the regular components of beer. Compared to HPLC and GC methods, radioimmunoassays are less time-consuming and they do not require special/expensive laboratory equipment.[69] Nardini and Ghiselli[84] determined free and bound phenolic compounds (especially phenolic acids) in beer by using an HPLC system after addition of strong antioxidants and sequsterants (in order to protect the phenolics from oxidation), and addition of phenolics releasing agents from their bound state. They found that most of the phenolic acids in beer are bound. Individual phenolic compounds have been analyzed by thin layer chromatography (TLC).[70] These compounds have also been analyzed by electrophoresis.[47] Cummings et al.[71] analyzed phenolic compounds in beer using amperometric screen-printed carbon electrodes. They noted that chromatographic methods might require tedious sample preparation steps, which might compromise sample integrity. The fabrication of phenolic biosensors can be a good alternative to overcome the problems associated with the ‘traditional’ analytical methods. Biosensors fabricated from carbon paste and plat tissue have also been utilized to analysis complex flavanols in beer samples. [72–74] However, due to the poor mechanical stability of carbon paste and low sensitivity, these biosensors are applicable for brewing industry. Cummings et al.[71] employed bio-electrodes fabricated from three commercially-available, graphite-based printed electrodes. The enzyme tyrosinase was immobilized on the electrode using a straightforward polymerization step, which could be adapted for mass production purposes. Vanhoenacker et al.[75] analyzed (quantitatively) iso-α-acids and reduced iso-α-acids in beer by direct injection and liquid chromatography equipped with both UV and mass spectrometric detection. Direct injection of samples (after the filtration of beer matrices) into HPLC system has also been reported for the determination of phenolic compounds in beer. [76–78] In this regard, De Pascual-Teresa et al.[79] reported an HPLC separation and on-line detection (by diode-array spectroscopy) after a chemical reaction with p-dimethylaminocynnamaldehyde (DMACA). Extraction of these compounds in beer has also been performed by applying liquid-liquid extraction (LLE) with organic solvents.[67,80] Solid phase extraction (SPE) is also a common technique used for the preconcentration and purification of samples prior to HPLC analysis of phenolic compounds in wines and beer. [81–83] Separation of phenolic compounds in beer has been used by reversed-phase liquid chromatography followed by ultraviolet,[74,84] photodiode array,[85,86] fluorimetric,[80] electrochemical,[74,84,87,88] or mass spectrometric detection.[67] Garcia et al.[89] presented a method based on SPE followed by liquid chromatographic analysis with UV detection. In the brewing industry, HPLC-UV is an advanced analytical tool useful for the determination of phenolic acids. This method was applied for the quantitative analysis of phenolic acids in alcohol-free beer. HPLC analysis of organic/phenolic acids of beer can also be performed by applying two detectors. One is the amperometric electrochemical detection (ECD) and the other photodiode array detection (PDA). The most common phenolic acid in their study was m-coumaric acid followed by ferulic, o-cumaric, p-coumaric and 3-hydroxy-benzoic acids. However, vanilic, chlorogenic, homovanillic, p-hydroxy-benzoic, 2,6-dihydroxybenzoic, syringic, gallic, protocatechuic, caffeic and 3,5-dihydroxybenzoic acids were present in small quantities. Vanbeneden et al.[90] were able to quantify both hydroxycinnamic acids and their corresponding aroma-active volatile phenols in wort and beer by simple and rapid isocratic HPLC using amperometric electrochemical detection. The technique gave good specificity and sensitivity, and could therefore be used for routine monitoring of the mentioned compounds in beer. Prior to that study, simultaneous determination of hydroxycinnamic acids and volatile phenols was not a common practice. Separate analysis of hydroxycinnamic acids and volatile phenols has mainly been reported using HPLC system[74,77,88,89,91] but GC has also been used. [92–97] Pusecker et al.[98] determined hop and beer bitter acids (such as humulones, isohumulones, dihydroisohumulones and tetrahydroisohumulones) by coupling of HPLC to nucleic magnetic resonance spectroscopy (HPLC-NMR), using both on-line and stopped-flow techniques. NMR spectroscopy measurements afforded full structural information on hop bitter acids constituents of various hop products. Capillary zone electrophoresis (CZE) has gained acceptance as an alternative and complementary technique to HPLC for the food analysis. Main advantages of CZE are high separation efficiency, improved selectivity, low operational cost and a higher speed of analysis.[99,100] A principle known as coelectroosmotic capillary electrophoresis (CE) has also been used for the analysis of phenolic compounds.[101,102] The total amount of polyphenols in beer and wine have been analyzed by spectrophotometric and fluorometric methods.[44,80,103] Viscosity-associated proteins (with high molecular weight) can be determined using different instrumental methods (section 4). Dissolved CO₂ content in beer might be analyzed using “Zahm volumeter” comprising two instruments: one for the sampling and bulk analysis of nonpackaged beer and other for the direct analysis of the packaged beer. Exopolysacchradies (ropy polysaccharides) produced by contaminating bacteria such as lactic acid bacteria has been qualitatively and quantitatively determined using combined methods of one- and two-D NMR spectroscopy (¹H and ¹³C), nano-electrospray-chemical ionization detector (ES-CID) tandem mass spectrometry and gel chromatography.[7,63,64] Selected publications applying beer body analysis tests are listed in Table 4.

Table 4 Selected publications regarding body analysis of beer

Parameter	Method of analysis	Source
Shear viscosity (rotational viscosity)	Rheometry using rheometer	[7]
Determination of dextrines content (viscosity enhancer)	Gel chromatography	[74]
Quantification of non-starch polysaccharides (NSP) content (viscosity enhancer and/or body destroyer)	GC and GC-MS by methylation analysis	[58–62]
Determination of viscosity-associated proteins (high-molecular weight)	(Table 1, foam)	(Table 1, foam)
Analysis of dissolved co2 content	Zahm volumeter	[11]
Qualification and quantification exopolysaccharides/ropy polysaccharides (viscosity enhancer and/or body destroyer)	Combination of nucleic magnetic resonance	[7,63, 64]
	Spectroscopy, nano ES-CID tandem mass spectroscopy and gel chromatography and gel chromatography
Determination of viscosity-associated polyphenoles	non-specific spectrophotometry based on the color formed at 600 nm with ferric ammonium citrate	[7]
	HPLC methodology	[66, 67, 74, 77, 84, 88, 89, 91]
	GC and combined GC-MS	[93–97, 104]
	TLC	[70]
	Capillary zone electrophoresis (CZE)	[47, 101, 102]
	Radioimmunoassay	[104]
	Amperiometric screen-printed carbon electrodes	[71]
	Phenolic biosensors/bioelectrodes	[71–74]
	Liquid chromatography by direct injection with ultraviolet absorbance detection or mass spectrometry	[67, 74–78]
	HPLC separation or liquid-liquid extraction (LLE) and on-line detection by diode-array spectroscopy after chemical reaction with DMACA	[67, 79, 80]
	Separation of phenolics by photodiode array, fluorimetry or electrochemical procedure	[74, 80, 85–88]
	HPLC coupled with NMR spectroscopy using both on-line and stopped-flow techniques	[98]
	Spectrophotometric and fluorometric methodologies	[44, 80, 103]
	Simple and rapid isocratic HPLC using amperometric electrochemical detection	[90]
	Solid-phase extraction followed by liquid chromatographic separation with ultraviolet detection	[89]

CONCLUSIONS

Foam, colloidal stability, color and transparency, and body of beer are among important sensory attributes of beer. In this article, major instrumental methods of analysis relevant to physical and physicochemical properties were discussed. These methods have been successfully applied for beer analysis. Ease of operation combined with a quick result is the most important characteristic one should look for when trying to select among several methods. Furthermore, adequate sensitivity (that is, a low detection limit) and selectivity as well as good accuracy and precision levels are expected in a typical method applied for beer analysis. It should be pointed out at the end that generally, there is a low correlation between instrumental analysis and sensory attributes (oral sensation) due to several reasons. For instance, instrumental measurements are usually carried out at temperatures different from mouth. The saliva lubrication function is absent in the former analysis. Mouth possesses considerably more temporal states than instrumental assessments during chewing and swallowing. The shear rates applied in mouth is usually significantly greater than those employed in instrumental measurements.