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Effect of Pressure on the Particle Size Distribution of Espresso Coffee 

2018, KIMIKA 
17 Views 6 Pages 
Studies regarding particle size distribution, particularly in espressos are surprisingly few. Particle size distribution (PSD) is a plot that displays the average diameter versus ...read more 
KIMIKA Volume 29, Number 2, pp. 30-35 (2018)   © 2018 Kapisanang Kimika ng Pilipinas
© 2018 Kapisanang Kimika ng Pilipinas(菲律宾卡皮萨南基米卡)
All rights reserved. Printed in the Philippines.
ISSN 0115-2130 (Print); 2508-0911 (Online)
ISSN 0115-2130(印刷版);2508-0911 (在线的)
https://doi.org/10.26534/kimika.v29i2.30-35 Effect of Pressure on the Particle Size   Distribution of Espresso Coffee   Erick Christofer I. Gonzales   1 , Karl Gabriel M. Lloren   1 , Jihan S. Al-shdifat   2 , Lica B. Valdez   3 , Krizzia Rae Gines, Emmanuel V. Garcia   1* 1 Chemistry Department, De La Salle University, Taft Avenue Manila 1004   2 Brownstone Asia-Tech Inc., Mandaluyong City 1552   3 Barista Cofee Academy o f Asia, San Juan City 1503   ABSTRACT   Studies regarding particle size distribution, particularly in espressos are surprisingly few. Particle size   distribution (PSD) is a plot that displays the average diameter versus percentage volume of the particles   present in a sample. With increased awareness amongst cofee drinkers, a study aiming to report the efects   of di ferent pressure on particle size distribution o f espresso from four di ferent cofee blends was conducted.   Te method involved pulling of espresso shots at 7, 9, and 11 bar (or atm) from di ferent cofee blends   labeled as MA, CO, AL, and MO. Laser difraction analysis showed diferent particle size groupings  for   each set of extraction pressure. Fine particles are within 1.20 to 28.70 µm. Te most abundant particle size   is centered at 185.4 µm. Te particle size distribution of co fee blends composed o f 100% Arabica co fee   (AL and MO) but sourced from di ferent locations, showed  four similar modes or size ranges centered at   3.523, 13.005, 28.70, and 185.4 µm regardless of the extraction pressure or the co fee source. On the other   hand, the cofee blends composed o f di ferent ratios o f Arabica and Robusta (MA and CO) showed di ferent   modes depending on the pressure. Tis indicates the potential of PSD for characterizing the purity of a   cofee blend. Te particle size distribution can also give insights as to the sensory attributes o f the espresso   cofee.   Keywords:  particle size distribution; laser difraction; arabica-robusta blend; espresso; pressure   INTRODUCTION   Cofee  has  been  among  the  most  traded   commodities around the world. Its consumption   has been increasing throughout the years with   consumers shifting their focus on to  favor quality   and distinctive sensory attributes (Sunarhanum  et   al. 铝。, 2014). Since favor is still the most important
, 2014).因为恩惠仍然是最重要的
consumer parameter, cofee drinkers nowadays
increasingly prefer specialty co
fee over non-specialty  非专业费用 ones. Specialty cofee is de
的。特色咖啡是 de
fned by its quality
from   farm to cup, which has been carefully handled
during harvesting, processing, drying, shipping, and
beverage preparation (SCAA, 2009). Te favor it
饮料制备(SCAA,2009)。Te favor it
imparts is found to be unique depending on species,
place of origin, climate, agricultural practices, and
extraction method. (Sunarharum, 2014).
提取方法。(Sunarharum,2014 年)。
Many extractions or brewing methods are available
in preparing a cup of co
fee. One o 费。一 of which is with
f 与
the use of an espresso machine. According to
Mestdagh  梅斯特达et al. 等。, (2017), an espresso is a beverage
, (2017), 浓缩咖啡是一种饮料
that can be prepared from roast and ground co
fee   by means of hot water pressure applied for a short
period of time, to a compact roast and ground
cofee cake by a percolation machine to obtain a
*Author to whom correspondence should be addressed; email: emmanuel.garcia@dlsu.edu.ph
*应收信的作者;电子邮件: emmanuel.garcia@dlsu.edu.ph
Volume 29, Number 2, July 2018
第 29 卷第 2 期, 2018 年 7 月 •
KIMIKA  喜米卡 Efect o f Pressure on the Particle Size Distribution of Espresso Co
f 对浓缩咖啡颗粒分布的压力
fee  31 small concentrated foamy cup. Te key parameters
identifed  已识别for this preparation method are, water to
cofee ratio, particle size, compaction, pressure, and
配fee ratio、粒径、压实度、压力和
brewing time. Among these, the extraction pressure
has the main infuence on the acquired favor
profle o 教授f an espresso because it is also a dependent
f 浓缩咖啡,因为它也是一个依赖
variable with respect to the permeability of co
fee   beds (Corrochano, 2015). A research conducted by
Andueza  安杜埃萨et al. 等。, (2002) concentrated on the efect
, (2002) 集中于 efect
of water pressure in the physicochemical, sensory
characteristics, and essential odorants of Arabica
espresso. However scientifc studies are still lacking
to substantiate seeming impact of such key variables
on cup quality.  关于杯子质量。 Te grinding process of roasted co
fee beans are related
to a particular brewing method in that an average
grind size is deemed appropriate for each method. In
the preparation of espresso, a certain amount of
fne  FNE的 particles (< 100 µm) are needed for pressure build-
压力建立需要颗粒 (< 100 μm)
up. Tese directly afect both permeability and
向上。Tese 直接影响渗透率和
fow   of water (i.e. low permeability of co
fee bed results  收费床结果 to higher extraction pressures, low total fow rate,   and longer extraction times, thus leading to over-   extraction and change in taste). For this reason,   studies were done regarding the ground cofee   beans, relating its particle size distribution on favor   release (Malvern, 2012), along with investigating the   efects o f various brewing techniques and particle   size of ground co fee on sensory pro fling (Fibrianto   et al. , 2018). We surmised that pressure during   cofee processing can in fuence the bean  fracturing   dynamics, and therefore the  fnal size distribution.   However, a cursory survey of the literature reveals   very limited reports focusing on the particle size   distribution in espressos, hence this study.   In line with the rising demand for high-quality co fee   alongside increased consumer awareness amongst   cofee drinkers (Per fect Daily Grind, 2017), the aim   of this work is to investigate the e fects o f various   pressures: 7, 9, and 11 bar (or atm) in the particle   size distribution of espresso obtained from four   diferent cofee blends by means o f laser di fraction   analysis.   METHODOLOGY   Materials and Reagents.  Te grinding of co fee   beans were carried out using a Rancilio Kyro   65 OD. Te holder of the ground co fee was a   ridged VST Inc. precision flter basket (58 mm   in diameter, 20-22g nominal capacity, and 30   mm height). Extraction process using an espresso   machine, commonly termed as pulling, was done   using the Milano Italy Bezzera Arcadia Display.   Plastic containers for biological samples were used   to contain the espresso samples. To prevent further   dissolution of co fee particles, the sample containers   were placed in an ice-flled chiller during the brie f   transport to the laboratory. Te samples were then   analyzed using the Beckmann Coulter LS 13 320   Laser Difraction Particle Size Analyzer equipped   with Universal Liquid Module using a 1.5mL liquid   dropper. Distilled water was used for the rinsing and   suspension of sample in the liquid module of the   instrument.   Collection of Samples.  Two cofee species are used   in this study: Cofea canephora (Robusta) and   Cofea arabica (Arabica). Four commercial variants   of the co fee beans having diferent compositions   and origins were used for the preparation the   espresso shots. Cofee blend MA is 60% Arabica   and 40% Robusta in medium-dark roast. Cofee   blend CO is 20% Arabica and 80% Robusta in   medium dark roast. Cofee blend-AL is 100%   Arabica from Ethiopia, and Co fee blend MO is also   100% Arabica but sourced from di ferent regions   in Central America. Both AL and MO blends were   roasted at a light level. Twenty (20) grams of co fee   grounds were collected per extraction. Te ground   cofee samples were then compacted in a porta   flter a component o f the espresso machine that   holds the ground cofee prior to and during the brewing process, and using an accessory used for compression called a tamper. Afterwards, espresso shots were pulled at various pressures of 7, 9, and 11 bar (or atm). Extraction temperature was fxed at 95±1ºC and weight of cofee grounds were set at 35 g per shot. Samples were immediately transferred to plastic containers and refrigerated. All extracted samples were prepared by a seasoned barista at the Barista and Cofee of Asia Association (BCAA). Particle Size Distribution Analysis. Vigorous swirling of the sample was done prior to the particle size analysis, to ensure homogeneity in aqueous solution. Samples were placed in the sample holder with a use of a dropper. Te following parameters were set on the LS 13 320 Laser Difraction Particle Size Analyzer: auto-rinsing for 15 seconds, de- bubbling for 142 seconds, measuring ofset for 60 seconds, aligning for 30 seconds, and measuring background for 60 seconds. Modes or peaks are the particle sizes that pinpoint a large abundance in a sample. Calibration of the Instrument. Glass beads with a known particle sizes and distribution were analyzed before and after the series of analyses. Te data was then compared with the accepted value prescribed by the instrument. Te standard procedure in calibrating the instrument was used in running the samples so as to avoid any diferences in the results basing from the parameters set.