Computer Percolation Models for Espresso Coffee: State of the Art, Results and Future Perspectives

Abstract

Coffee is one of the most consumed beverages in the world. This has two main consequences: a high level of competitiveness among the players operating in the sector and an increasing pressure from the supply chain on the environment. These two aspects have to be supported by scientific research to foster innovation and reduce the negative impact of the coffee market on the environment. In this paper, we describe a mathematical model for espresso coffee extraction that is able to predict the chemical characterisation of the coffee in the cup. Such a model has been tested through a wide campaign of chemical laboratory analyses on espresso coffee samples extracted under different conditions. The results of such laboratory analyses are compared with the simulation results obtained using the aforementioned model. The comparison shows a close agreement between the real and in silico extractions, revealing that the model is a very promising scientific tool to take on the challenges of the coffee market.

Influence of Flow Rate, Particle Size, and Temperature on Espresso Extraction Kinetics

“…Additionally, 5-CQA is known to be affected strongly by different roasting processes [41,42], which could further explain the concentration differences between the two studies. For TDS, the measured values were in accordance with Angeloni et al [13].…”

“…In the literature, relative standard deviations (RSD) of <5-10% [19,23,24] for either component concentration or mass in the cup are generally reported but can reach up to 20% [13]. The average relative standard deviation for the studied experimental set was 2.5%, with the highest RSD of 8.5%.…”

“…The use of different coffee and water types, roasting levels, coffee puck masses, beverage sizes, and extraction machines impeded quantitative comparisons to other studies. Angeloni et al, who also used a 20 g Arabica coffee puck and a ~BR 1/2, extracted, on average, 3.39 mg g −1 trigonelline, 5.18 mg g −1 caffeine, 5.27 mg g −1 5-CQA, and 10.02 g (100 g) −1 TDS [13]. Taking into consideration that Caprioli et al reported trigonelline masses in the cup ranging from 28.20 mg to 65.08 mg and caffeine masses from 116.87 mg to 199.68 mg for the same extraction settings (7.5 g ground coffee, 25 mL EC, 25 s) for 20 different EC coffee brands, the experimental results were within the expected range [24].…”

“…The grinding process defines the particle size distribution and the amount of coffee mass in the portafilter. Finer grinding levels (GL) increase the particle surface area in contact with water, enabling a higher extraction yield for trigonelline, caffeine, and 5-caffeoylquinic acid (5-CQA) [13][14][15][16][17]. Increasing the ground coffee mass at a similar extracted EC volume increases the masses of trigonelline, caffeine, and 5-CQA in the cup [18,19].…”

“…Higher water temperatures (T) increase the components' solubility and reduce water viscosity [26]. However, the influence of water temperature on EC component mass in the cup has been inconclusive for experiments with otherwise constant conditions [13]. Albanese et al [27] analyzed coffee pods and reported increased caffeine concentration with rising temperatures from 90 • C to 110 • C. Masella et al [28] found no significant difference in trigonelline, caffeine, and chlorogenic acid concentrations in the EC cup for 75 • C, 80 • C, or 85 • C. For similar EC components, Andueza et al [29] reported several ambiguous temperature correlations for significant differences between EC brewed at 88 • C, 92 • C, 96 • C, and 98 • C. Also, Salamanca et al [30] described different influences on the caffeine and 5-CQA concentrations in the cup for upward and downward temperature gradients between 88 • C and 93 • C without identifying a conclusive correlation.…”