Stout Beers Research Articles

Pilsen, Red Ale and Stout brewer’s spent grain: polyphenols, antioxidant and antihypertensive activities, and physicochemical properties

The objective of this work was to evaluate the concentration of phenolic compounds, the antioxidant and anti-hypertensive capacity, and the physicochemical characteristics of brewer’s spent grain (BSG) from Pilsen, Red Ale and Stout beers. Results indicate that the studied byproducts present high concentration of total polyphenols, flavonols and phenolic acids. The evaluation of antioxidant potential revealed up to 60.9% scavenging of ABTS radicals, 12.3% of DPPH radicals and 12.4% of iron chelating power. In addition, 64.6% inhibition of angiotensin-I-converting enzyme was observed, suggesting anti-hypertensive capacity. Results of water and oil absorption capacity indicates that BSG powders presents similar values to cereal flours. CIELab values show that Pilsen BSG present light-yellow color, meanwhile Red Ale and Stout preferably dark color. The BSG powder presents pH values lower than 5.0, indicating acid conditions, which may contribute to bacterial stability for medium to long term storage of the dried residues. The present work shows that the BSG can be an alternative source of functional compounds, representing a sustainable way of industrial waste management.

Target profiling of beer styles by their iso-α-acid and phenolic content using liquid chromatography-quadrupole time-of-flight-mass spectrometry.

Beer styles show wide variation in color, flavor, and clarity, due to differences in their chemical content. Some of the major flavor compounds in beer are isomerized alpha acids and phenolic compounds. These were investigated as potentially discerning features between beer styles. A selection of 32 American beers covering five styles was analyzed using liquid chromatography quadrupole time-of-flight mass spectrometry, which resulted in high mass accuracy chromatograms of the studied analytes. Distinctions between the presence or relative concentrations of certain compounds were observed and related back to brewing ingredients and procedures. For example, vanillin was only observed in stout beers due to the use of roasted barley malts for brewing, while chlorogenic acid isomers were found in two sours at relatively high concentrations (189 and 34mg/L) because of the fruits used to flavor the beers. Distinctions were further confirmed using multivariate analysis techniques, which separated three of the five beer styles (India pale ales, stouts, and sours).

Bubble cascade may form not only in stout beers.

In a glass of stout beer, a very large number of small dispersed bubbles form a texture motion of a bubble swarm moving downwards. Such a cascading motion is caused by a gravity-driven hydrodynamic instability and depends on the interbubble distance. To estimate these two corresponding indicators, an experimentally measured velocity profile is required and, thus, is obtained a posteriori. However, it is unknown why the bubble cascade is observed only in stout beer with nitrogen, such as Guinness beer. To address this question via a priori estimation, here, we develop a mathematical continuum model of film flow in bubbly liquid, uncovering the essential dynamics among many physical processes occurring simultaneously in a glass. To validate the proposed model, we perform a numerical simulation of the distribution of massless Lagrangian particles in an inclined container. We investigate the effects of particle concentration, inclination angle, particle diameter, and container size on the cascading film flow. The results reveal that the motion and waviness of clear-fluid film can be successfully estimated a priori to experiments or simulations. Moreover, it is found that the continuum behavior of particles in the film flow is analogous to the continuum description of rarefied gas dynamics. These findings explain how the cascading bubbles in a pint glass of stout beer satisfy the continuum assumption and suggest a general condition for the onset of the cascade, for instance, a 200-l drum for carbonated water.

Sorghum Coffee–Lactose Stout Production and Its Physico-Chemical Characterization

Sorghum (Safrari) was valorized into sorghum coffee-lactose stouts using Vernonia amygdalina as a bittering ingredient. These sorghum grains and subsequent sorghum pale malt were tested for their acceptability in the brewing field. Results obtained were the germinative capacity of 99.29 ± 0.58%, a germinative energy of 98.56 ± 1.79%, a thousand corns weight 48.08 ± 0.02 g for the grains, and a diastatic power of 187.44 ± 7.89 WK for sorghum malt. The worts and beers produced were characterized and were found suitable. Moreover, alcohol content in stout beers obtained was between 8.8% and 9.4% ABV. Sensory evaluation was implemented on beers using 30 panellists and the best combination was the one using 50% lactose (250 g) and 50% coffee (250 g) in 5 L of wort during wort boiling.

The in vitro antithrombotic properties of ale, lager, and stout beers

The in vitro antithrombotic properties of polar lipid microconstituents of three Irish beers (ale, larger, and stout) have been assessed against platelet-activating factor-induced platelet aggregation. Total lipid (TL) extracts were obtained using the Bligh and Dyer method and each beer was separated into the organic phase and hydromethanolic phase. The total polar lipid (TPL) and total neutral lipid (TNL) fractions of the organic phase and hydromethanolic phase of each beer were obtained using a counter-current distribution. The TL, TNL, and TPL extracts of each phase of each beer were measured for their capacity to inhibit platelet-activating factor-induced platelet aggregation. The low IC50 values obtained suggest that all three beers contain potent polar lipids that can inhibit platelet-activating factor-induced platelet aggregation. The fatty acid composition of the organic phase TPL extracts were measured using gas chromatography-mass spectrometry. The organic phase total polar lipid extracts were further fractionated using thin-layer chromatography (TLC) and the antithrombotic bioactivities of these TLC bands were measured. This data suggested that the TLC bands corresponding to phosphatidylcholine, phosphatidylethanolamine, sphingomyelin, and cardiolipin were the most active phospholipids in the total polar lipids of the organic phase. These promising results indicate that beer consumption may provide antithrombotic effects.

Sinking bubbles in stout beers

A surprising phenomenon witnessed by many is the sinking bubbles seen in a settling pint of stout beer. Bubbles are less dense than the surrounding fluid so how does this happen? Previous work has shown that the explanation lies in a circulation of fluid promoted by the tilted sides of the glass. However, this work has relied heavily on computational fluid dynamics (CFD) simulations. Here, we show that the phenomenon of sinking bubbles can be predicted using a simple analytic model. To make the model analytically tractable, we work in the limit of small bubbles and consider a simplified geometry. The model confirms both the existence of sinking bubbles and the previously proposed mechanism.

Mycotoxin profiling of 1000 beer samples with a special focus on craft beer.

Currently beer is booming, mainly due to the steady rise of craft breweries worldwide. Previous surveys for occurrence of mycotoxins in beer, were mainly focussed on industrial produced beer. The present survey reports the presence of mycotoxins in craft beer and how this compares to industrial produced beer. More than 1000 beers were collected from 47 countries, of which 60% were craft beers. A selection of 1000 samples were screened for the presence of aflatoxin B1, ochratoxin A (OTA), zearalenone (ZEN), fumonisins (FBs), T-2 and HT-2 toxins (T-2 and HT-2) and deoxynivalenol (DON) using a mycotoxin 6-plex immunoassay. For confirmatory analysis, a liquid chromatography tandem mass spectrometry (LC-MS/MS) method was developed and applied. The 6-plex screening showed discrepancies with the LC-MS/MS analysis, possibly due to matrix interference and/or the presence of unknown mycotoxin metabolites. The major mycotoxins detected were DON and its plant metabolite deoxynivalenol-3-β-D-glucopyranoside (D3G). The 6-plex immunoassay reported the sum of DON and D3G (DON+D3G) contaminations ranging from 10 to 475 μg/L in 406 beers, of which 73% were craft beers. The popular craft beer style imperial stout, had the highest percentage of samples suspected positive (83%) with 29% of all imperial stout beers having DON+D3G contaminations above 100 μg/L. LC-MS/MS analysis showed that industrial pale lagers from Italy and Spain, predominantly contained FBs (3–69 μg/L). Besides FBs, African traditional beers also contained aflatoxins (0.1–1.2 μg/L). The presence of OTA, T-2, HT-2, ZEN, β-zearalenol, 3/15-acetyl-DON, nivalenol and the conjugated mycotoxin zearalenone 14-sulfate were confirmed in some beers. This study shows that in 27 craft beers, DON+D3G concentrations occurred above (or at) the Tolerable Daily Intake (TDI). Exceeding the TDI, may have a health impact. A better control of brewing malts for craft beer, should be put in place to circumvent this potential problem.

Some Topics on the Physics of Bubble Dynamics in Beer

Besides being the favorite beverage of a large percentage of the population, a glass or bottle of beer is a test bench for a myriad of phenomena involving mass transfer, bubble-laden flows, natural convection, and many more topics of interest in Physical Chemistry. This paper summarizes some representative physical problems related to bubbles that occur in beer containers, pointing out their practical importance for the industry of beverage processing, as well as their potential connection to other processes occurring in natural sciences. More specifically, this paper describes the physics behind the sudden foam explosion occurring after a beer bottled is tapped on its mouth, gushing, buoyancy-induced motions in beer glasses, and bubble growth in stout beers.

Why do bubbles in Guinness sink?

Stout beers show the counter-intuitive phenomena of sinking bubbles, while the beer is settling. Previous research suggests that this phenomenon is due to the small size of the bubbles in these beers and the presence of a circulatory current, directed downwards near the side of the wall and upwards in the interior of the glass. The mechanism by which such a circulation is established and the conditions under which it will occur has not been clarified. In this paper, we use simulations and experiments to demonstrate that the flow in a glass of stout beer depends on the shape of the glass. If it narrows downwards (as the traditional stout glass, the pint, does), the flow is directed downwards near the wall and upwards in the interior and sinking bubbles will be observed. If the container widens downwards, the flow is opposite to that described above and only rising bubbles will be seen.

Food product development using sorghum and millets: opportunities and challenges

Sorghum and millets are uniquely well-adapted to cultivation in the harsh environmental conditions of the semi-arid tropics. For Africa and India, they represent attractive materials for developing food and beverage manufacturing enterprises; in contrast to wheat and barley that often cannot be locally cultivated economically. For example, notable technological and commercial success has been achieved in Africa with the replacement of barley malt with sorghum in the production of lager and stout beers and non-alcoholic malt beverages. Sorghum and millets also have a several valuable attributes that are increasing being exploited in food and beverage products. Their most important attribute is that they are the basis of many local traditional African and Indian foods such as porridges, flatbreads, snacks and fermented non-alcoholic and alcoholic beverages. By application of cereal science and technology, safe and economic manufacturing processes are being developed for many of these traditional products or derivatives of them. Such products are generally aimed at the rapidly growing urban market. Three levels of grain value-addition can be identified, which demand increasingly sophisticated skills, but are suitable for SME-type manufacture: 1. Clean grain and simple flours, 2. Composite and fortified flours, and 3. Ready-to-Eat foods and beverages. In Western countries, the attribute of sorghum and millets that is generating much interest and product development, is their health-promoting properties. They are especially rich in phytochemicals, particularly antioxidant phenolics, at levels similar to that of other rich sources such as berries. In fact, in the USA, particular sorghum varieties and products from them such as breakfast cereals are being promoted under the name ‘grain berry’. The other attribute of very wide interest in Western countries is that sorghum and millets do not contain wheat-like gluten proteins, and hence are suitable for consumption by coeliacs. Very rapid developments are taking place in the technology of gluten-free baked products. These technologies for health-promoting food products and gluten-free baked goods need to be adapted for general production of sorghum and millet-based breads and other food products in Africa and India. A major challenge is to substantially reduce the cost of the gluten-free technologies, in order to provide an affordable good quality non-wheat based bread-type product to meet the rapidly growing demand for bread. However, the biggest challenge for Africa and India is simply the economic cultivation of sorghum and millets. Their agricultural productivity must be substantially improved in order to reduce the costs of these grains to make them more economically attractive alternatives to imported cereals such as maize, wheat and barley. More fundamentally, improvement in the productivity of sorghum and millets will contribute substantially to food security and economic development in Africa and India.

Foaming in stout beers

We review the differences between bubble formation in champagne and other carbonated drinks, and stout beers which contain a mixture of dissolved nitrogen and carbon dioxide. The presence of dissolved nitrogen in stout beers gives them several properties of interest to connoisseurs and physicists. These remarkable properties come at a price: stout beers do not foam spontaneously and special technology, such as the widgets used in cans, is needed to promote foaming. Nevertheless, the same mechanism, nucleation by gas pockets trapped in cellulose fibers, responsible for foaming in carbonated drinks is active in stout beers, but at an impractically slow rate. This gentle rate of bubble nucleation makes stout beers an excellent model system for investigating the nucleation of gas bubbles. The equipment needed is modest, putting such experiments within reach of undergraduate laboratories. We also consider the suggestion that a widget could be constructed by coating the inside of a beer can with cellulose fibers.

Bubble nucleation in stout beers

Bubble nucleation in weakly supersaturated solutions of carbon dioxide-such as champagne, sparkling wines, and carbonated beers-is well understood. Bubbles grow and detach from nucleation sites: gas pockets trapped within hollow cellulose fibers. This mechanism appears not to be active in stout beers that are supersaturated solutions of nitrogen and carbon dioxide. In their canned forms these beers require additional technology (widgets) to release the bubbles which will form the head of the beer. We extend the mathematical model of bubble nucleation in carbonated liquids to the case of two gases and show that this nucleation mechanism is active in stout beers, though substantially slower than in carbonated beers and confirm this by observation. A rough calculation suggests that despite the slowness of the process, applying a coating of hollow porous fibers to the inside of a can or bottle could be a potential replacement for widgets.

Inhibitory effects of beer on heterocyclic amine-induced mutagenesis and PhIP-induced aberrant crypt foci in rat colon

Anti-mutagenic and anti-carcinogenic effects of beer on heterocyclic amine (HCA)-induced carcinogenesis were studied in vitro and in vivo. Four commercial beers (two pilsner-type, black, and stout) showed inhibitory effects against five HCAs, 2-amino-3,8-dimethylimidazo [4,5-f]quinoxaline (MeIQx), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2), 2-amino-6-methyldipyrido[1,2-a:3′,2′-d]imidazole (Glu-P-1) and 2-amino-3-methylimidazo[4,5-f]-quinoline (IQ), in the Ames assay using Salmonella typhimurium TA98 in the presence of rat S9 mix. The inhibitory effects of dark-colored beers (stout and black beer) were greater than those of pilsner-type beers. Dark-colored beers suppressed CYP1A2 activity in a dose-dependent manner, suggesting that inhibition of HCA activation is partly responsible for their strong anti-mutagenic effects. Anti-mutagenic effects were also observed when the pooled human S9 mix or activated IQ was used in the assay. The micronucleus test using Chinese hamster lung CHL/IU cells showed that the addition of freeze-dried samples of pilsner-type and stout beer to the culture medium significantly reduced the number of cells with micronuclei induced with PhIP or Trp-P-2. Single-cell gel electrophoresis assay (comet assay) revealed that oral ingestion of pilsner-type and stout beers for 1 week significantly inhibited DNA damage in the liver cells of male ICR mice exposed to MeIQx (13mg/kg, i.p.). A decrease in the formation of DNA adducts was also observed using a 32P-postlabeling method. Male Fischer 344 rats orally received PhIP (75mg/kg, five times a week for 2 weeks) and aberrant crypt foci (ACF) formation in the colon was analyzed after 5 weeks. The number of ACF was significantly reduced in rats fed a diet containing freeze-dried beer. These results suggest that beer inhibits the genotoxic effects of HCAs and may reduce the risk of carcinogenesis caused by food borne carcinogens.

A Comparison of Alternative High-Performance Liquid Chromatographic Systems for Measuring Bitterness in Beer

Alternative systems for measurement by high-performance liquid chromatography of iso-α-acids in highly bittered stout beers were evaluated in an examination of contributions to error in the assay. The objective was to devise rapid and accurate systems for measuring iso-α-acids in pre-isomerized hop extracts and in stout beers bittered either partially or wholly with pre-isomerized extract. Special attention was paid to the preparation of standards, pretreatment of beer samples, calibration protocols, calibration frequency, chromatographic mobile phases and measurement wavelength. Variability between assays was smallest (coefficient of variation <3%) when a simplified sample pretreatment was used, in which high-molecular-weight interferences were removed from stout beers by precipitation with methanol. The main cause of assay variability was changes in the shape, area, and resolution of peaks, a tendency that was greater during chromatography with ion-pairing mobile phases than with ion-suppressing mobile phases. This change was not compensated for by internal standardization but was countered by increasing calibration frequency with “spiked blanks.” Accordingly, chromatographic variability with a single calibration cycle was minimized (cv 0.4%). Samples of stout beers containing 35–100 mg/L of iso-α-acids before bottling were shown to contain only about 70–95% of their iso-α-acid contents in solution after storage in bottles for three months at 18°C. Losses in soluble iso-α-acids were greatest in those beers containing high addition rates of pre-isomerized hop extracts.

A Comparison of Alternative High-Performance Liquid Chromatographic Systems for Measuring Bitterness in Beer

Alternative systems for measurement by high-performance liquid chromatography of iso-α-acids in highly bittered stout beers were evaluated in an examination of contributions to error in the assay. ...