The present paper describes a flow-injection system coupled to a Micro-Guard cartridge and a miniaturized optical CCD detection system used to monitor the sugars (glucose/fructose) and ethanol content during alcoholic fermentation. The carrier stream (mobile phase) is composed of an aqueous sulfuric acid solution. The flow parameters were studied in order to obtain a good resolution and a wide dynamic concentration range, with a good repeatability. The relative standard deviation (RSD) obtained was inferior to 4%, for n = 3. It was possible to achieve a linear range of up to 12 g L -1 of sugars and up to 2% (v/v) of ethanol with a detection limit of 2.3 g L -1 and 0.4% (v/v), for sugars and ethanol concentrations, respectively. The proposed system was successfully applied to monitor a vinification process by the quantification of sugars and ethanol, and also in some finished port wines.