This article is to study the criteria of dehydration model, and to establish the Brixter index. Coffee cherries ( Coffea arabica L. var. catimor) were selected from two different farms in Pangkhon village, Chiang Rai province, which are in the northern part of Thailand: Farm A, and Farm B. The low air temperatures (18–30 °C) and low relative humidities (65–30%) technique (LTLH) was gradiently applied, to dehydrate the coffee bean, leading to higher sugar concentration. The applicability of the various measurements, such as physicochemical properties, dehydration kinetic, Brix boosting parameters, and their correlations were investigated. The level of soluble solids (°Brix) and acid concentrations in coffee samples were analyzed, to determine the °Brix/acid and o Brix*pH 2 ratios. The qualities of coffee cherries changes depending on the decreasing level of moisture content during the dehydration process. The °Brix degree reveals that by the end of the dehydration process, the sugar concentration of coffee cherries has increased by 1.5 times that of its initial. The °Brix/acid, and o Brix*pH 2 ratios highly correlated to the amount of soluble solids ( r 2  = 0.923 and 0.972, respectively) within coffee cherries. The most suitable timing to select dehydrating coffee cherries for the fermentation process is when the coffee cherries have attained °Brix/acid ratio of > 10 to 33, and o Brix*pH 2 ratio of > 400 to 850. These ratios can be used as an efficient instrument to determine the optimum Brix boosting stage of coffee cherry in the LTLH system.