A method for measuring the alcohol concentration of an acetic acid fermentation broth which comprises (a) forming a sample gas containing volatile components present in the acetic acid fermentation broth, the volatile componentscomprising alcohol and acetic acid; (b) passing the sample gas through an absorption column packed with a material which binds acetic acid whereby the acetic acid is absorbed on the material; (c) passing the sample gas which has passed through the absorption column to a gas sensor for measuring the alcohol content of the gas by outputting an electrical signal which correlates to the alcohol content of the sample gas; and (d) determining the alcohol content of the sample gas in response to the electrical output signal from the gas sensor. The invention also provides a method of forming the sample gas by passing a sample of the fermentation broth through a water-repellent gas permeable tube mounted in a hollow cell and passing a carrier gas through the hollow cell whereby volatile components from the fermentation broth inside of the tube diffuse through the gas permeable tube wall and are intermixed with the carrier gas to form the sample gas containing the volatile components.