Editing Ethanol (section)

=== Testing ===
[[File:EthanolMIRInfraredSpectra.PNG|class=skin-invert-image|thumb|upright=1.35|Infrared reflection spectra of liquid ethanol, showing the −OH band centered near 3300&nbsp;cm<sup>−1</sup> and C−H bands near 2950&nbsp;cm<sup>−1</sup>]]
[[File:Ethanol near IR spectrum.png|class=skin-invert-image|thumb|upright=1.35|[[Near-infrared spectrum]] of liquid ethanol]]

Breweries and [[biofuel]] plants employ two methods for measuring ethanol concentration. Infrared ethanol sensors measure the vibrational frequency of dissolved ethanol using the C−H band at 2900&nbsp;cm{{sup|−1}}. This method uses a relatively inexpensive solid-state sensor that compares the C−H band with a reference band to calculate the ethanol content. The calculation makes use of the [[Beer–Lambert law]]. Alternatively, by measuring the density of the starting material and the density of the product, using a [[hydrometer]], the change in specific gravity during fermentation indicates the alcohol content. This inexpensive and indirect method has a long history in the beer brewing industry.