Longer roasting raises pH (decreases acidity). See: http://www.idosi.org/wasj/wasj2%285%29/17.pdf http://www.idosi.org/wasj/wasj2%285%29/17.pdf Note that the i

Longer roasting raises pH (decreases acidity). See: http://www.idosi.org/wasj/wasj2%285%29/17.pdf http://www.idosi.org/wasj/wasj2%285%29/17.pdf Note that the initial time of small decrease of pH corresponds to under-roasted coffee, and coffee with this degree of roast would be unacceptable even to fans of light roasts.