The kinetics and mechanism of caffeine infusion from coffee: The effect of particle size

Abstract

Measurements have been made of the rate of infusion of caffeine into distilled water from medium roast Kenyan Arabica coffee beans and from eight sieved fractions of the ground beans at 25.8"C. The first-order rate constants increased dramatically as the particle size decreased. For one of the size fractions the rate constants were then measured at various temperatures up to 84.1"C and were found to rise eight-fold over this temperature interval. The partition coefficients of caffeine between ground beans and water were also determined. These results, interpreted by a new steady-state theory of extraction, show that the rate-determining step in the infusion is diffusion of caffeine through the swollen coffee particles. The low magnitude of the diffusion coefficient and its high activation energy demonstrate that caffeine diffusion within the bean particles is a hindered process.

Comparison of nine common coffee extraction methods: instrumental and sensory analysis

“…In general, of course, the extraction efficiency increases with decreasing particle size, as was shown, for example, by Andueza et al [62] and Spiro et al [63].…”

The Kinetics and Mechanism of Caffeine Infusion from Coffee: the Temperature Variation of the Hindrance Factor

“…The present paper presents the results of similar experiments at 25¡C where H was ca 30 (Spiro and Selwood 1984). Because the hindrance factor here was so much larger, it was hoped that the various factors contributing to slow intra-bean di †usion could be more clearly identiÐed.…”

“…The rate-determining step in co †ee brewing has been shown to be the di †usion of co †ee solubles such as caffeine through the ground co †ee beans (Spiro and Selwood 1984 ;Spiro 1988). The steady-rate theory of extraction then allows one to determine the intra-bean di †usion coefficient of (say) ca †eine from the Ðrst-D bean order rate constant k by the equation…”

Aqueous extraction kinetics of soluble solids, phenolics and flavonoids from sage (Salvia fruticosa Miller) leaves

“…There are several studies on extraction behavior of different plant materials such as coffee bean (Spiro and Selwood 1984), soy bean (Jokic et al 2010), feijoa fruit (Tuncel and Yılmaz 2013), grape seeds (Bucic-Kojic et al 2007), turmeric (Sogi et al 2010), fumitory (Rakotondramasy-Rabesiaka et al 2008), cassia seeds (Medoua and Mbofung 2007) and olive leaves (Carcel et al 2010). These studies were conducted in aqueous form or solvent extraction based on the above mentioned parameters.…”