Neglected Food Bubbles: The Espresso Coffee Foam

Illycaffè S.p.A, Via Flavia 110, Trieste, 34147 Italy.
Food Biophysics (Impact Factor: 1.63). 09/2011; 6(3):335-348. DOI: 10.1007/s11483-011-9220-5
Source: PubMed


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.

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Available from: Luciano Navarini
    • "A very large number of espressos coffees (EC) are brewed every day in the world. It has been estimated that over than 50 million cups per days are consumed (Illy and Navarini, 2011). Consequently , many coffee brewing apparatuses have been developed (Klopprogge et al., 2013) and it is known that different brewing techniques produce different espressos in term of quality (Parenti et al., 2014). "
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    ABSTRACT: A new espresso brewing method has recently been developed. The main steps are: introduction and tamping of ground coffee in a sealed chamber, introduction of pressurized air into the chamber, the introduction of hot water and a pre-infusion phase. It is substantially different to the usual brewing method used in bars: the driving force for the flow is the pressure difference between the interior and the exterior of the chamber (rather than pressurized hot water provided by a motor-driven pump); the extraction process is partially static; the pressure is higher than the traditional method; and the temperature of the extraction chamber can be controlled (in addition to the water temperature control found in the traditional method). The method has been tested with three chamber temperatures and two pressures. At all settings, espressos produced using this method have particularly high and persistent foam. Furthermore, changes in pressure cause changes in some physical parameters and the amount of key odorants in the headspace above the coffee. A benchmark comparison with the capsule method gives differences in several aromatic compounds and in almost all the physical parameters. In conclusion, the beverage produced by the CF method is clearly recognizable by a thick and very persistent foam layer, while the method appears more flexible than the traditional one as the characteristics of the EC can be adjusted as a function of brewing conditions.
    No preview · Article · Feb 2015 · Journal of Food Engineering
    • "In fact an expert consumer can immediately detect from foam colour, texture and persistency dissimilarity possible errors in grinding, percolation, temperature or extraction level (Illy and Navarini, 2011). Physically the crema is a biphasic system compounded by a gas phase surrounded by a liquid phase, named lamellae. "
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    ABSTRACT: Espresso coffee is the most popular choice for Italian coffee consumers. It has been estimated that every day, in the world, over of 50 million of Espresso cups are taken. As a consequence of this success, a large number of devices to make Espresso have been developed. In this scenario, a new device has been recently developed and patented (Eu. Patent 06 023 798.9; US 2010/0034942 A1). This brew method, named “Caffè Firenze”, uses a sealed extraction chamber, where water and gas provides pressure higher than the other extraction methods. Three main parts compose the apparatus: the gas source, the extraction chamber and the heat exchanger. The gas source provides the pressured gas required to raise the pressure of the system. The extraction chamber is made with chrome-brass and accessorized with two heating glow plugs. Many are the factors affecting Espresso quality: it is known that, coffee type, roasting conditions and degree, grinding and storage strongly affect the obtained brew. Also, several studies have been carried out on the effect of the setting parameters on quality, for example water pressure, water temperature, and brew time. Among the characteristics that determine Espresso quality, the main attribute for the visual analysis is, without doubts, the foam, also called “crema”. Indeed, height, aspect, and persistency of foam are features much appreciates by consumers. Two distinguish Espresso foam parameters are the persistency and foam index. Equipping a commercial bar machine with the new designed extraction chamber makes feasible the comparison between the traditional way to brew Espresso and the new device. The comparison was made holding the previous mentioned conditions, and differences were evaluated in terms of physical parameters and aromatic profiles. Caffè Firenze shows pronounced differences compared with traditional Espresso in term of foam-related parameters. Also, the new extraction device produces coffees with higher values of body-related parameters, such density and viscosity. The two kinds of Espressos are perceived different at visual analysis and taste by a panel test.
    No preview · Article · Jun 2013 · Journal of Agricultural Engineering
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    ABSTRACT: Molecular dynamics simulations were carried out on several systems of caffeine interacting with simple sugars. These included a single caffeine molecule in a 3 m solution of α-d-glucopyranose, at a caffeine concentration of 0.083 m, a single caffeine in a 3 m solution of β-d-glucopyranose, and a single caffeine molecule in a 1.08 m solution of sucrose (table sugar). Parallel nuclear magnetic resonance titration experiments were carried out on the same solutions under similar conditions. Consistent with previous thermodynamic experiments, the sugars were found to have an affinity for the caffeine molecules in both the simulations and experiments, and the binding in these complexes occurs by face-to-face stacking of the hydrophobic triad of protons of the pyranose rings against the caffeine face, rather than by hydrogen bonding. For the disaccharide, the binding occurs via stacking of the glucose ring against the caffeine, with a lesser affinity for the fructose observed. These findings are consistent with the association being driven by hydrophobic hydration and are similar to the previously observed binding of glucose rings to various other planar molecules, including indole, serotonin, and phenol.
    Full-text · Article · Aug 2012 · The Journal of Physical Chemistry B
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