The schlieren effect was evaluated employing a homemade LED-based photometer furnished with flow cell of long optical pathlengths, which was exploited as a tool to develop an automated photometric procedure for reagentless ethanol determination in distilled ethanolic beverages. The analytical procedure employed a multicommuted flow analysis manifold, using solenoid mini-pumps for fluid propulsion. Aiming to evaluate if schlieren effect would be or not affected by the length of the flow cell, the photometer was designed to be coupled to flow cells with optical pathlengths ranging from 50 to 250 mm. The control of the flow system and the data acquisition were performed using an Arduino Due microcontroller coupled to a microcomputer through the serial interface, which was programmed to work as a slave. Under optimal operational conditions (sampling loop length, flow cell optical pathlength and LED emission wavelength), the magnitude of the signal generated by the schlieren effect was linearly related to ethanol concentration in aqueous medium from 2.5 to 60% (v/v), r = 0.9994. The efficacy of this procedure was ascertained by performing ethanol determination in distilled ethanolic beverages, yielding results in agreement with those achieved using the AOAC official method at the 95% confidence level. Other useful features include a sampling rate of 52 determinations per hour, a detection limit of 0.8% ethanol and a standard deviation of 1.8% (n = 9) for a typical sample containing 38.6% (v/v) ethanol. (C) 2016 Elsevier B.V. All rights reserved.