abstractEspressocoffee extraction i

abstract
Espressocoffee extraction is the most common brewing method in Italy and it is becoming very popular in many other countries around the world. Water (including its ionic content) is an essential ingredient and its role inEspressobrewing must be taken into due consideration. It is well known that water treatment is necessary to remove possible off-flavours deriving from the disinfection performed at municipal waterworks as well as to prevent expensive professionalEspressocoffee machine from scaling problems. However, there is little awareness of the direct effect of water composition on the quality of coffee beverages, particularly forEspressocoffee. In this paper, the state of the art is reviewed with emphasis of water/coffee components interaction during the brewing process. The role played by alkalinity and selected cations on sensory properties of Espressocoffee is discussed.

1. Introduction
Water is the second essential ingredient for coffee brewing, and, from a quantitative point of view, it is the most important. Several early studies have been focussed at individuating possible correlation between water (and its ionic content) and coffee beverage quality (Gardner, 1958; Lockhart, Tucker, & Merritt, 1955; Pangborn, 1982; Pangborn, Trabue, & Little, 1971; Tassan & Russell, 1974). These studies have been carried out by using filter or drip coffee extraction as coffee beverage sample preparation method. In the typical set-up, a paper filter is placed in a proper coneshaped holder. Medium ground coffee is put into the filter and the holder placed on top of a glass jug. Boiled water is poured into
the filter and allowed to seep through. The resulting coffee beverage is a clean, transparent system (Petracco, 2001). In a wide range of natural mineralised drinking waters, differences in the visual
attributes of brewed coffee often were greater than differences in flavour (Pangborn, 1982). However, electrolytes in both natural drinking waters and in model water systems adversely influenced
the quality of the resultant beverages (Pangborn et al., 1971). In particular the carbonates were the worst offenders, resulting in a bitter, flat coffee. Moreover, although a certain degree of acidity
is characteristic of brewed coffee, the sourness of coffee prepared from distilled water has been found to be excessive (Pangborn et al., 1971). The relevance of water alkalinity in influencing (neutralising) coffee acidity has been evidenced by Sivetz (1972).In particular, ‘‘for each 100 ppm of water alkalinity, the pH is raised about 0.22 unit for roast and ground coffees and about 0.33 unit for instant coffees” (Sivetz, 1972). It has been also found that the concentration and species of ions in solution change the rate at which water passes through the bed of ground coffee, thereby causing differential extraction of coffee solids (Gardner, 1958). Carbonates and bicarbonates with excessive sodium ions have been found to affect the brewing time, both having a retarding effect in direct relation to their concentration, while all other ions normally present in municipal water supplies appeared to have little effect, if any on brewing time (Gardner, 1958). For this reason, Gardner (1958)suggested to avoid the use of ion exchange (replacement of calcium and magnesium with sodium) to treat water containing a high concentration of bicarbonate. More recently, water quality affecting the taste of filter or drip
coffee beverage has been discussed in terms of the presence of foreign flavours due to disinfecting treatments (chlorination) and of water hardness, being the latter investigated in detail (Cammenga
& Zielasko, 1997). In fact, if, on one hand, possible foreign flavours directly affect the coffee taste, on the other hand, water hardness through its scaling potential, indirectly affect the beverage quality
by reducing heat transfer effectiveness of heat exchangers and then affecting the extraction temperature. In spite of the increasing popularity of the Espresso coffee extraction as a coffee preparation method around the world, little is known about the role played by water and its ionic content in beverage quality and acceptability.Espresso– the word refers to a preparation made on request expressly for the occasion – is brewed by rapidly percolating a small quantity of pressurised,
heated water through a compressed cake of finely ground roasted coffee. The process is applied (brewing time) until the beverage volume in the cup meets the personal preferences of the consumer
and/or the regional traditions, in Italy, for instance, this falls in the range 15–50 ml, with an optimal outcome at 25–30 ml (regular Espressowith a brewing time of 25–30 s). The resulting beverage,
differently from drip coffee, must be topped by a velvety thick, reddish-brown foam calledcremato be considered properly prepared and to be appreciated by connoisseurs. This peculiar brewing method requires specialised and costly equipment that can heat water to a temperature of 92–94 C and then pressurise it to 9 ± 2 bar (Illy, 2002). The detrimental effect of foreign flavours as well as of water
hardness in Espresso brewing is well documented (Petracco, 2001; Schulman, 2002). However, as far as we know, only two papers reported quantitative data on the effects of water composition
and water treatment onEspressocoffee brewing (Fond, 1995; Rivetti et al., 2001). Moreover, the role played by water composition on thecremaproperties has not yet been the subject of study. As
matter of fact, the few reports onEspressocoffee foam mainly focused on its chemical aspects and interfacial properties neglecting the effect of water ingredient (D’Agostina et al., 2004; Ferrari,
Navarini, Liggieri, Ravera, & Suggi Liverani, 2007; Navarini, Ferrari, Suggi Liverani, Liggieri, & Ravera, 2004; Nunes, Coimbra, Duarte, & Delgadillo, 1997). In this paper, the state of the art is reviewed with emphasis of water/coffee components interaction during the brewing process. Alkaline scale formation and sodium softening chemistry is briefly discussed in view of its relevance inEspressocoffee quality. Moreover, new experimental data on the effect of water composition on Espressocoffee foam is also reported and discussed.