Dynamic tensiometric characterization of espresso coffee beverage

Does Coffee Have Terroir and How Should It Be Assessed?

The terroir of coffee is defined as the unique sensory experience derived from a single origin roasted coffee that embodies its source. Environmental conditions such as temperature, altitude, shade cover, rainfall, and agronomy are considered the major parameters that define coffee terroir. However, many other parameters such as post-harvest processing, roasting, grinding, and brewing can combine to influence the perception of terroir. In this review, we discuss the contribution of these parameters and their influence on coffee terroir. Assessment of terroir requires defined sensory descriptors, as provided by the World Coffee Research Lexicon, and standardized roast level, grind size, and brew method. The choice of the post-harvest processing method is often environmentally dependent, suggesting that an inclusion into the coffee terroir definition is warranted. Coffee terroir is often not intentionally created but results from the contributions of the Coffea species and variety planted, environmental and agricultural parameters, and both the harvest and post-harvest method used. The unique combination of these parameters gives the consumer a unique cup of coffee, reminiscent of the place the coffee was produced.

Robust Superamphiphobic Fabrics with Excellent Hot Liquid Repellency and Hot Water Vapor Resistance

Superamphiphobic surfaces progress rapidly but suffer from the issues of low repellency to hot liquids, complicated and nonaqueous preparation methods, and low durability. Here, a simple waterborne approach is developed to fabricate robust superamphiphobic fabrics with excellent hot liquid repellency and hot water vapor resistance. First, a perfluorodecyl polysiloxane (FD-POS) aqueous suspension was prepared by hydrolytic cocondensation of (3-glycidyloxy propyl)trimethoxysilane and 1H,1H,2H,2H-perfluorodecyltriethoxysilane with SiO₂ particles. Then, the superamphiphobic fabrics were fabricated by dipping polyester fabrics in the suspension, which were then cured. The fabrics show excellent superamphiphobicity owing to the combination of the hierarchical micro-/nanostructure and FD-POS with very low surface energy. The superamphiphobic fabrics feature excellent hot liquid repellency even for a large volume of 130.0 °C soybean oil and condensed small droplets from ∼90.0 °C water vapor. This is attributed to its high superamphiphobicity, excellent hot water vapor resistance, and outstanding thermal durability. In addition, the superamphiphobic fabrics exhibit high mechanical and chemical durability against washing, abrasion, and immersion in corrosive or organic liquids. Thus, hot liquid repellent superamphiphobic fabrics may find applications in various fields such as antiadhesion of various hot liquids and in efficiently preventing scalding.

Lipidomic and metabolomic profiles of Coffea canephora L. beans cultivated in Southwestern Nigeria

Coffee (Coffea spp.) is one of the most popular refreshing beverages globally. Coffee lipid diversity has untapped potential for improving coffee marketability because lipids contribute significantly to both the health benefits and cup quality of coffee. However, in spite of its potential importance, there have not been extensive studies of lipids among C. canephora genotypes. In this study, ultra-performance liquid chromatography coupled with mass spectrometry (UPLC-MS) profiling of lipid molecules was performed for 30 genotypes consisting of 15 cultivated and 15 conserved genotypes of C. canephora in Southwestern Nigeria. We identified nine classes of lipids in the 30 genotypes which belong to the 'Niaouli', 'Kouillou' and 'Java Robusta' group: among these, the most abundant lipid class was the triacylglycerols, followed by the fatty acyls group. Although 'Niaouli' diverged from the 'Kouillou' and 'Java Robusta' genotypes when their lipid profiles were compared, there was greater similarity in their lipid composition by multivariate analysis, compared to that observed when their primary metabolites and especially their secondary metabolite profiles were examined. However, distinctions could be made among genotypes. Members of the fatty acyls group had the greatest power to discriminate among genotypes, however, lipids that were low in abundance e.g. a cholesterol ester (20:3), and phosphotidylethanolamine (34:0) were also helpful to understand the relationships among C. canephora genotypes. The divergent lipid profiles identified among the C. canephora genotypes, correlated with their Single Nucleotide Polymorphism grouping as assessed by genotype-by-sequencing, and will be exploited to improve coffee cup quality.

Physical and Chemical Effects of Different Working Gases in Coffee Brewing: A Case Study of Caffè Firenze

(1) Background: Recently, a new espresso extraction method, Caffè Firenze, has been developed, which uses gas at operating pressures of 20 bar to obtain abundant, persistent foam. The experiment aimed to evaluate the effect of using six gases (air, argon, nitrogen, carbon dioxide, carbon/nitrogen mix, and nitrous oxide) on the foam and liquid coffee. (2) Methods: Foam volume, persistence, sugar retention time, color, and rheological properties were measured. Volatile organic compounds were also evaluated. Analyses were also carried out on the liquid coffee to determine caffeine and chlorogenic acid concentrations. (3) Results: The analysis of variance revealed significant differences between the gases for all parameters. Multivariate analysis identified three groups of gases: the first comprised air, N₂, and Ar; the second CO₂ and N₂O; and the third comprised samples extracted with CO₂/N₂ mix. (4) Conclusions: The choice of gas significantly influences the drink’s chemical-physical characteristics and is fundamental for product diversification.

Swelling properties of roasted coffee particles

BACKGROUND

In this study, the swelling behavior of roasted coffee particles in water and particularly its impact on particle diameter is examined by applying laser-diffraction analysis and microscopy. Several potential influencing factors are investigated: initial particle size, roasting degree, and temperature. Additionally, the time dependency of swelling and particle shape is evaluated at two different temperatures.

RESULTS

We verify that particle erosion occurs - as observed by an increase of the fine particle fraction after wetting - and it is revealed that this effect is more pronounced with a rise in temperature. The total relative increase in particle size is determined as approximately 15% based on a broad range of different sized coffee grounds. It is demonstrated that the degree of swelling is independent of both the initial particle diameter and the roasting degree. The particle shape is found to be unaffected by swelling. This research reveals that swelling is initially quick, with 60-80% of the final steady-state diameter being reached after 30 s and completed after 4 min of wetting, i.e. within the timescale of conventional coffee brewing methods.

CONCLUSION

This work provides a better understanding of the impact of wetting as part of the coffee brewing process, thus aiding the design, modeling, and optimization of coffee extraction. It clarifies the strong deviation of previous results on coffee-particle swelling by considering particle erosion and degassing and provides a robust method for quantification. © 2020 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Unraveling the science of coffee foam - a comprehensive review

Coffee foam is the frothy layer that forms above the liquid phase of espresso and instant coffee beverages. While the carbon dioxide formed during roasting is responsible for crema formation in espresso, gasification is the established foaming approach in instant coffee. The protein-like fractions and polysaccharides extracted from roasted coffee promote foamability and foam stability, respectively. Crema of consolidated texture retains the volatile aromatic substances and prevents the espresso from cooling too rapidly. Further, an inverse relationship has been observed between foam persistence and volatility of aroma molecules above the cup. Gasified spray-dried instant coffee exhibited an accelerated delivery rate of hydrophobic aroma compounds. Thus, foam is the signature of a high-quality cup of coffee. Despite its various functionalities, coffee foam is scarcely investigated owing to its metastable nature. Only recently, the chemical, structural, and interfacial rheology properties of the coffee foam have been looked at. The current study intends to review the scientific knowledge acquired on coffee foam, thus far. The initial sections describe the general attributes and functions of espresso and instant coffee foam. Further, the mechanisms of formation and stabilization of coffee foam are detailed, followed by the factors influencing the same. The following discussions focus on the role of coffee foam in determining the sensory and aroma release characteristics of the beverages. The scope for future research in this field of study is highlighted in the concluding section.

The impact of different filter baskets, heights of perforated disc and amount of ground coffee on the extraction of organics acids and the main bioactive compounds in espresso coffee

Espresso coffee (EC) is a complex and much appreciated beverage among coffee consumers. The extraction phase of EC, a combination of physical and chemical variables in a very short time, has a direct effect on the flavour of the beverage. This research aims to optimize the extraction process of EC by decreasing the amount of ground coffee from 14 g to 12 g (double cup), while keeping constant the particle size of ground coffee and the physical parameters of the espresso machine, making use of the following accessories: two different filter baskets, and four different heights of perforated discs (4-7 mm). Quantitative analyses on several organic acids (acetic, citric, caffeic, malic, tartaric) and caffeine, trigonelline, nicotinic and 5-caffeoylquinic acid are carried out with HPLC-VWD through a newly developed method. This combines the quantification of organic acids, obtained through HPLC-VWD, with the results of a sensory panel evaluation on the descriptive notes of EC. The outcomes will trigger and support further studies on different extraction processes, to develop more sustainable and economically affordable coffee of high quality.

Emanating Jets As Shaped by Surface Tension Forces

We show that emanating jets can be regarded as growing liquid towers, which are shaped by the twofold action of surface tension: first the emanated fluid is being accelerated back by surface tension force, herewith creating the boundary conditions to solve the shape of the liquid tower as a solution of an equation mathematically related to the hydrostatic Young-Laplace equation, known to give solutions for the shape of pending and sessile droplets, and wherein the only relevant forces are gravity g and surface tension γ. We explain that for an emanating jet under specific constraints all mass parts with density ρ will experience a uniform time dependent acceleration a( t). An asymptotic solution is subsequently numerically derived by making the corresponding Young-Laplace type equation dimensionless and by dividing all lengths by a generalized time dependent capillary length λ_c( t) = [Formula: see text]. The time dependent surface tension γ( t) can be derived by measuring both time dependent acceleration a( t) and time dependent capillary length λ_c( t). Jetting experiments with water and coffee show that the dynamic surface tension behavior according to the emanating jet method and with the well-known maximum bubble pressure method are the same, herewith verifying the proposed model.

Extraction of espresso coffee by using gradient of temperature. Effect on physicochemical and sensorial characteristics of espresso

Espresso extraction is generally carried out at a fixed temperature within the range 85-95°C. In this work the extraction of the espressos was made in a new generation coffee machine that enables temperature profiling of the brewing water. The effect of using gradient of temperature to brew espressos on physicochemical and sensorial characteristics of the beverage has been investigated. Three different extraction temperature profiles were tested: updrawn gradient (88-93°C), downdrawn gradient (93-88°C) and fixed temperature (90°C). The coffee species investigated were Robusta, Arabica natural and Washed Arabica. Results proved that the use of gradient temperature for brewing espressos allows increasing or decreasing the extraction of some chemical compounds from coffee grounds. Moreover an appropriate gradient of temperature can highlight or hide some sensorial attributes. In conclusion, the possibility of programming gradient of temperature in the coffee machines recently introduced in the market opens new expectations in the field of espresso brewing.

Influence of foam structure on the release kinetics of volatiles from espresso coffee prior to consumption

The relationship between the physical structure of espresso coffee foam, called crema, and the above-the-cup aroma release was studied. Espresso coffee samples were produced using the Nespresso extraction system. The samples were extracted with water with different levels of mineral content, which resulted in liquid phases with similar volatile profiles but foams with different structure properties. The structure parameters foam volume, foam drainage, and lamella film thickness at the foam surface were quantified using computer-assisted microscopic image analysis and a digital caliper. The above-the-cup volatile concentration was measured online by using PTR-MS and headspace sampling. A correlation study was done between crema structure parameters and above-the-cup volatile concentration. In the first 2.5 min after the start of the coffee extraction, the presence of foam induced an increase of concentration of selected volatile markers, independently if the crema was of high or low stability. At times longer than 2.5 min, the aroma marker concentration depends on both the stability of the crema and the volatility of the specific aroma compounds. Mechanisms of above-the-cup volatile release involved gas bubble stability, evaporation, and diffusion. It was concluded that after the initial aroma burst (during the first 2-3 min after the beginning of extraction), for the present sample space a crema of high stability provides a stronger aroma barrier over several minutes.

Neglected Food Bubbles: The Espresso Coffee Foam

Coffee beverage known as espresso, must be topped by a velvety thick, reddish-brown foam called crema, to be considered properly prepared and to be appreciated by connoisseurs. In spite of the relevant role played by crema as a quality marker, espresso coffee foam has not yet been the subject of detailed investigations. Only recently, some aspects of the Physics and Chemistry behind the espresso coffee foam have attracted the attention of scientists. In addition to sharing several characteristics with other food foams like beer foam, for instance, the espresso coffee foam may contain solid particles (minute coffee cell-wall fragments), it is subjected to a remarkable temperature gradient and its continuous phase is an oil in water emulsion rendering it a very complex system to be studied. Moreover, in the typical regular espresso coffee cup volume (serving) of 25-30 mL, crema represents at least 10% of the total volume, and this is a limitation in obtaining experimental data by conventional instruments. The present work is aimed at reviewing the literature on espresso coffee foam. The traditional espresso brewing method will be briefly described with emphasis on the steps particularly relevant to foam formation and stabilization. In addition to present up-dated experimental data on surface properties at solid/beverage and air/beverage interface, recent advances on the espresso foam formation mechanism, as well as on foam stability, will be critically examined. The key role played by carbon dioxide generated by roasting and the effects of low and high-molecular-weight coffee compounds in promoting/inhibiting the espresso coffee foam will be discussed and emphasized.

Is coffee a functional food?

Definitions of functional food vary but are essentially based on foods' ability to enhance the quality of life, or physical and mental performance, of regular consumers. The worldwide use of coffee for social engagement, leisure, enhancement of work performance and well-being is widely recognised. Depending on the quantities consumed, it can affect the intake of some minerals (K, Mg, Mn, Cr), niacin and antioxidant substances. Epidemiological and experimental studies have shown positive effects of regular coffee-drinking on various aspects of health, such as psychoactive responses (alertness, mood change), neurological (infant hyperactivity, Alzheimer's and Parkinson's diseases) and metabolic disorders (diabetes, gallstones, liver cirrhosis), and gonad and liver function. Despite this, most reviews do not mention coffee as fulfilling the criteria for a functional food. Unlike other functional foods that act on a defined population with a special effect, the wide use of coffee-drinking impacts a broad demographic (from children to the elderly), with a wide spectrum of health benefits. The present paper discusses coffee-drinking and health benefits that support the concept of coffee as a functional food.