Changes in the Aromatic Profile of Espresso Coffee As a Function Of
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Article pubs.acs.org/JAFC Changes in the Aromatic Profile of Espresso Coffee as a Function of the Grinding Grade and Extraction Time: A Study by the Electronic Nose System C. Severini,* I. Ricci, M. Marone, A. Derossi, and T. De Pilli Department of Science of Agricultural, Food and Environment (SAFE), University of Foggia, Via Napoli 25, 71122 Foggia, Italy ABSTRACT: The changes in chemical attributes and aromatic profile of espresso coffee (EC) were studied taking into account the extraction time and grinding level as independent variables. Particularly, using an electronic nose system, the changes of the global aromatic profile of EC were highlighted. The results shown as the major amounts of organic acids, solids, and caffeine were extracted in the first 8 s of percolation. The grinding grade significantly affected the quality of EC probably as an effect of the particle size distribution and the percolation pathways of water through the coffee cake. The use of an electronic nose system allowed us to discriminate the fractions of the brew as a function of the percolation time and also the regular coffee obtained from different grinding grades. Particularly, the aromatic profile of a regular coffee (25 mL) was significantly affected by the grinding level of the coffee grounds and percolation time, which are two variables under the control of the bar operator. KEYWORDS: espresso coffee, electronic nose system, aroma profile, extraction time, grinding grade − ■ INTRODUCTION different fractions,16 20 while wide range of literature reports ff ff the qualitative and quantitative characterization of volatiles of The Italian espresso co ee (EC) is the most consumed co ee 21,22 beverage in the world. Particularly because its appreciated an EC cup. sensorial properties, over than 50 million cups are consumed For instance, using chromatography/mass spectrometry every day.1 EC may be defined as “a brew obtained by (GC/MS) and GC/olfactometry (GC/O), over 1000 volatiles and 70 odorants have been identified from EC;23,24 never- percolation of hot water under pressure through compacted 25 cake of roasted ground coffee, where the energy of the water theless, these techniques are expensive and time-consuming. pressure is spent within the cake”.2 On the other hand, sensory analysis has been extensively used ff to evaluate and discriminate the sensorial attributes of coffee, As well-known, the quality of EC is a ected by several fl variables, some of which are managed by the industry, such as particularly the aroma and avor, but some disadvantages of this technique include subjectivity and poor reproducibil- the coffee varieties, roasting conditions, roasting degree, − − 26 28 mixture of roasted coffee varieties, and storage conditions.3 7 ity. Other variables are under the control of the barista (i.e., the In the last few years, one of the most promising applications technician of the bar), such as the temperature and pressure of in routine quality control of foods and beverages is the water, grinding grade, weight of coffee grounds (dose), and electronic nose that is a new technology that enables the ff acquisition of the sensory analysis for the detection of the pressure on the upper surface of co ee cake (tamping); also, fi these variables significantly affect the physical, chemical, and overall aromatic pro le of samples. In particular, the electronic − sensorial attributes of EC.1,7 12 nose attempts to emulate the mammalian nose using an array of Moreover, the extraction time is of crucial importance sensors simulating mammalian olfactory responses to the aroma.29 The sensors respond to a broad range of volatiles because the overall quality of EC is the result of the equilibrium ffi of hundreds of chemical compounds.13 In general, a regular that have a high a nity with aldehydes, alcohols, ketones, etc. coffee of 25 mL is obtained with an extraction rate of 1 mL/s, These compounds are drawn across the sensor array and induce but several differences are commonly observed. For instance, a reversible physical and/or chemical change in the sensing the so-called ristretto coffee (about 15 mL) and lungo coffee material, which causes a change in electrical properties, such as (about 30 mL) are often consumed in Italy and in other conductivity. These changes are transducers into electrical 14 signals, which are pre-processed and conditioned before countries. Under this point of view, for a correct management fi 30 31 and an accurate standardization of EC quality, a precise identi cation by a pattern recognition system. Aishima and Pornpanomchai et al.,32 using the electronic nose, classified description of the kinetic extraction of all chemical compounds ff ff is of great importance, but this aspect has not been subjected to di erent types of instant co ee on the basis of their aromatic fi profiles, while other researchers used electronic nose to scienti c experiments in details; indeed, the majority of the ff ff ff ff papers available in the literature focused their attention on the di erentiate commercial co ee brands, di erent co ee varieties extraction and analysis of aromatic compounds, sugars, solids, lipids, proteins, caffeine, etc.13,15,16 Received: November 26, 2014 Also, even though the EC is considered the most aromatic Revised: February 6, 2015 − coffee brew17 19 very few papers focused their efforts on the Accepted: February 9, 2015 changes of volatiles over extraction time, separating the brew in Published: February 9, 2015 © 2015 American Chemical Society 2321 DOI: 10.1021/jf505691u J. Agric. Food Chem. 2015, 63, 2321−2327 Journal of Agricultural and Food Chemistry Article or different roasting grades, and the presence of defects on distribution commonly detectable in the bars. Then, the particle size roasted coffee and to estimate the shelf life of packaged distribution for each grinding level was described shaking 100 g of − coffee.33 39 Furthermore, the electronic nose system was coffee grounds with four sieves (600, 400, 250, and 180 μm) until a applied on EC to determine the best time for packaging40 of constant weight. Table 2 shows the percentage of distribution of the coffee grounds, to discriminate the coffee from different particle sizes for each grinding level. production countries and roasting degrees,24 and to classify ff 41 Table 2. Distribution (%) of Particle Size in Each Grinding beans, grounds, and brew of commercial co ee blends. ff ± Particularly, in this work, the authors reported that a correct Grade of Co ee Powder (Mean Values Standard distinction of the brews was not statistically significant. Deviation) On the basis of the above considerations, the purpose of this grinding grade paper was to study the changes of the EC during extraction to particle size (μm) 6 6.5 7 obtain useful information for the better management of the ± ± ± brew quality. More specifically, the main objective was to use >600 0.21 0.11 0.68 0.22 2.93 0.53 ± ± ± the electronic nose system to study the changes of the overall 400 < X < 600 5.69 1.26 13.80 0.82 33.87 1.63 ± ± ± aromatic profile of EC, taking into account the extraction time 250 < X < 400 32.00 4.89 47.15 14.12 35.64 1.88 ± ± ± and the grinding level of coffee powder as independent 180 < X < 250 52.60 6.12 37.18 14.10 26.42 1.07 ± ± ± variables. <180 9.52 3.21 1.19 1.02 1.15 0.85 ■ MATERIALS AND METHODS Each EC sample was divided into three fractions (F) collecting the Raw Materials and EC Preparation. Roasted coffee beans brews obtained in the first 8 s (Ft1), from 9 to 16 s (Ft2), and from 17 (medium-dark roasting: L* = 21.50, a* = 5.92) were supplied from to 24 s (Ft3) of extraction. These extraction times were chosen by ESSSE caffèS.p.A. (Anzola dell’Emilia, Bologna, Italy). The beans dividing in three fractions the time necessary to prepare a regular were ground by an automatic grinder with flat grinding blades (model coffee that is 25 s. The extraction times were measured using a digital Super Jolly coffee grinder for a grocery, Mazzer, Italy) having eight timer. The regular EC of 25 mL, from each grinding level, was levels of grinding: 1 for the finest and 8 for the coarsest. Water prepared measuring the volume of brew through a graduate cylinder. “Leggera” (Gaudianello S.p.A., Italy) used for brew preparation was At least 20 replicates were performed for each espresso, obtaining a locally purchased. Table 1 reports the main physical and chemical total of 240 samples. Physical and Chemical Analyses. The pH of the samples was Table 1. Physicochemical Characteristics of Mineral Water measured by a pH-meter model Basic 20 (Crison, Allen) previously “ ” calibrated with three buffers at pH 4.00, 7.00, and 9.00. Also, acidity Leggera (Gaudianello, Italy) as Listed on the Label of the ff Bottle was measured by titration of 25 mL of co ee brew at room temperature with 0.1 N NaOH until pH of 7.00.43 The total solids analytical parameter value content was measured gravimetrically by drying about 3 mL of EC at 44 a 105 °C until a constant weight. pH 7.30 ff ° μ The ca eine content was measured using the method described by conductivity at 20 C( S/cm) 510 45 fi ° Skoog et al., with some modi cations. Each EC brew (fractions and total residue at 180 C (TDS) (mg/L) 416 regular coffee) was previously filtered with 0.22 μm nylon filter (Olim ́ silica (SiO2) (mg/L) 105 Peak, Teknokroma Anlitica, Spain) and directly injected (injection potassium (K+) (mg/L) 32 volume = 20 μL) into a high-performance liquid chromatography calcium (Ca2+) (mg/L) 46 (HPLC) binary pump (Waters model 1525, Milford, MA) equipped magnesium (Mg2+) (mg/L) 14 with a detector set at 254 nm (Waters model 2487, Milford, MA).